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What type of organism is commonly used in preparation of foods such as cheese and yogurt?
|
[
"protozoa",
"gymnosperms",
"mesophilic organisms",
"viruses"
] |
C
|
Mesophiles grow best in moderate temperature, typically between 25°C and 40°C (77°F and 104°F). Mesophiles are often found living in or on the bodies of humans or other animals. The optimal growth temperature of many pathogenic mesophiles is 37°C (98°F), the normal human body temperature. Mesophilic organisms have important uses in food preparation, including cheese, yogurt, beer and wine.
Some kinds of cheese also, kefir, kumis (mare milk), shubat (camel milk), ayran, cultured milk products such as quark, filmjölk, crème fraîche, smetana, skyr, and yogurt
The yeast species Saccharomyces cerevisiae is an important model organism in cell biology. The fruiting bodies of some larger fungi are collected as edible mushrooms, including delicacies like the chanterelle, cep, and truffle, while a few species are cultivated. Mould fungi provide the meaty (umami) flavour of fermented soybean products such as tempeh, miso and soy sauce, and contribute flavour and colour to blue cheeses including Roquefort and Stilton.
Microbial food cultures are live bacteria, yeasts or moulds used in food production. Microbial food cultures carry out the fermentation process in foodstuffs. Used by humans since the Neolithic period (around 10 000 years BC) fermentation helps to preserve perishable foods and to improve their nutritional and organoleptic qualities (in this case, taste, sight, smell, touch). As of 1995, fermented food represented between one quarter and one third of food consumed in Central Europe.
They most likely found out how to ferment milk by chance and in all likelihood, yogurt was discovered independently in this way in many different places at different times. The cuisine of ancient Greece included a dairy product known as oxygala (οξύγαλα) which was a form of yogurt.
Most illnesses associated with low-moisture foods or IMFs have been caused by Salmonella spp. To reduce the risk of bacterial growth, products are treated with a combination of low pH, addition of sugar, salt and preservatives, and a thermal process that can eliminate pathogens and extend shelf-life. In the case of yeasts and molds, chemical preservatives such as sorbates and propionates are used to inhibit their growth.
|
What phenomenon makes global winds blow northeast to southwest or the reverse in the northern hemisphere and northwest to southeast or the reverse in the southern hemisphere?
|
[
"coriolis effect",
"muon effect",
"centrifugal effect",
"tropical effect"
] |
A
|
Without Coriolis Effect the global winds would blow north to south or south to north. But Coriolis makes them blow northeast to southwest or the reverse in the Northern Hemisphere. The winds blow northwest to southeast or the reverse in the southern hemisphere.
The trade winds blow westward in the tropics, and the westerlies blow eastward at mid-latitudes. This wind pattern applies a stress to the subtropical ocean surface with negative curl across the north Atlantic Ocean. The resulting Sverdrup transport is equatorward. Because of conservation of potential vorticity caused by the poleward-moving winds on the subtropical ridge's western periphery and the increased relative vorticity of northward moving water, transport is balanced by a narrow, accelerating poleward current, which flows along the western boundary of the ocean basin, outweighing the effects of friction with the western boundary current known as the Labrador current. The conservation of potential vorticity also causes bends along the Gulf Stream, which occasionally break off due to a shift in the Gulf Stream's position, forming separate warm and cold eddies. This overall process, known as western intensification, causes currents on the western boundary of an ocean basin, such as the Gulf Stream, to be stronger than those on the eastern boundary.
However, vertical flows over Africa and the Americas are more marked in boreal winter.At longer interannual timescales, variations in the Hadley circulation are associated with variations in the El Niño–Southern Oscillation (ENSO), which impacts the positioning of the ascending branch; the response of the circulation to ENSO is non-linear, with a more marked response to El Niño events than La Niña events. During El Niño, the Hadley circulation strengthens due to the increased warmth of the upper troposphere over the tropical Pacific and the resultant intensification of poleward flow. However, these changes are not asymmetric, during the same events, the Hadley cells over the western Pacific and the Atlantic are weakened.
The trade winds (also called trades) are the prevailing pattern of easterly surface winds found in the tropics near the Earth's equator, equatorward of the subtropical ridge. These winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. The trade winds act as the steering flow for tropical cyclones that form over world's oceans, guiding their path westward. Trade winds also steer African dust westward across the Atlantic Ocean into the Caribbean sea, as well as portions of southeast North America.
That air can move to northeastern US if a large high pressure area is anchored in the Canadian Maritimes or the northern states. The high pressure system's clockwise flow directs cold moist air southward and westward into Northeast US.
Extratropical cyclones are generally driven, or "steered", by deep westerly winds in a general west to east motion across both the Northern and Southern hemispheres of the Earth. This general motion of atmospheric flow is known as "zonal". Where this general trend is the main steering influence of an extratropical cyclone, it is known as a "zonal flow regime".When the general flow pattern buckles from a zonal pattern to the meridional pattern, a slower movement in a north or southward direction is more likely. Meridional flow patterns feature strong, amplified troughs and ridges, generally with more northerly and southerly flow.Changes in direction of this nature are most commonly observed as a result of a cyclone's interaction with other low pressure systems, troughs, ridges, or with anticyclones.
|
Changes from a less-ordered state to a more-ordered state (such as a liquid to a solid) are always what?
|
[
"unbalanced",
"exothermic",
"reactive",
"endothermic"
] |
B
|
Summary Changes of state are examples of phase changes, or phase transitions. All phase changes are accompanied by changes in the energy of a system. Changes from a more-ordered state to a less-ordered state (such as a liquid to a gas) areendothermic. Changes from a less-ordered state to a more-ordered state (such as a liquid to a solid) are always exothermic. The conversion of a solid to a liquid is called fusion (or melting). The energy required to melt 1 mol of a substance is its enthalpy of fusion (ΔHfus). The energy change required to vaporize 1 mol of a substance is the enthalpy of vaporization (ΔHvap). The direct conversion of a solid to a gas is sublimation. The amount of energy needed to sublime 1 mol of a substance is its enthalpy of sublimation (ΔHsub) and is the sum of the enthalpies of fusion and vaporization. Plots of the temperature of a substance versus heat added or versus heating time at a constant rate of heating are calledheating curves. Heating curves relate temperature changes to phase transitions. A superheated liquid, a liquid at a temperature and pressure at which it should be a gas, is not stable. A cooling curve is not exactly the reverse of the heating curve because many liquids do not freeze at the expected temperature. Instead, they form a supercooled liquid, a metastable liquid phase that exists below the normal melting point. Supercooled liquids usually crystallize on standing, or adding a seed crystal of the same or another substance can induce crystallization.
Consider one particular type of phase transition: melting. When a solid is melting, crystal lattice chemical bonds are being broken apart; the substance is transitioning from what is known as a more ordered state to a less ordered state. In Fig. 7, the melting of ice is shown within the lower left box heading from blue to green.
The temperature at which a substance changes state from a solid to a liquid. It depends on pressure and is usually specified for a given substance under standard conditions. The melting point of a substance is identical to its freezing point.
Regarding biological membranes, the liquid ordered phase is a liquid crystalline phase of a lipid bilayer, and is of significant biological importance. It occurs in many lipid mixtures combining cholesterol with a phospholipid and/or sphingolipids e.g. sphingomyelin. This phase has been related to lipid rafts that may exist in plasma membranes.
Phase transition or phase change, takes place in a thermodynamic system from one phase or state of matter to another one by heat transfer. Phase change examples are the melting of ice or the boiling of water. The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation. Phase transitions involve the four fundamental states of matter: Solid – Deposition, freezing and solid to solid transformation.
Further compression of the surfactant molecules on the surface shows behavior similar to phase transitions. The ‘gas’ gets compressed into ‘liquid’ and ultimately into a perfectly closed packed array of the surfactant molecules on the surface corresponding to a ‘solid’ state. The liquid state is usually separated in the liquid-expanded and liquid-condensed states.
|
What is the least dangerous radioactive decay?
|
[
"beta decay",
"gamma decay",
"alpha decay",
"zeta decay"
] |
C
|
All radioactive decay is dangerous to living things, but alpha decay is the least dangerous.
The least stable is 15Ne with a half-life of 770(300) ys (7.7(3.0)×10−22 s). See isotopes of carbon for notes about the measurement. Light radioactive neon isotopes usually decay to fluorine or oxygen, while heavier ones decay to sodium.
Trace quantities are found in nature from neutron capture reactions by uranium atoms, a fact not discovered until 1951.Twenty-five neptunium radioisotopes have been characterized, with the most stable being 237Np with a half-life of 2.14 million years, 236Np with a half-life of 154,000 years, and 235Np with a half-life of 396.1 days. All of the remaining radioactive isotopes have half-lives that are less than 4.5 days, and the majority of these have half-lives that are less than 50 minutes. This element also has five meta states, with the most stable being 236mNp (t1/2 22.5 hours).
The remaining 6 transient elements (technetium, promethium, astatine, francium, neptunium, and plutonium) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements. No radioactive decay has been observed for elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium). Observationally stable isotopes of some elements (such as tungsten and lead), however, are predicted to be slightly radioactive with very long half-lives: for example, the half-lives predicted for the observationally stable lead isotopes range from 1035 to 10189 years.
The most prevalent radioactive gas detected was Radon, a noble gas that has no odor, no color, and no taste, and can also travel into the atmosphere or bodies of water. Radon is also directly linked to lung cancer, and is the second leading cause of lung cancer in the populace.All of these elements only deteriorate through radioactive decay, which is also known as a half-life. Half-lives of the nuclides previously discussed can range from mere hours, to decades.
It is the heaviest doubly magic nuclide known. A total of 43 lead isotopes are now known, including very unstable synthetic species. The four primordial isotopes of lead are all observationally stable, meaning that they are predicted to undergo radioactive decay but no decay has been observed yet. These four isotopes are predicted to undergo alpha decay and become isotopes of mercury which are themselves radioactive or observationally stable. In its fully ionized state, the beta decay of isotope 210Pb does not release a free electron; the generated electron is instead captured by the atom's empty orbitals.
|
Kilauea in hawaii is the world’s most continuously active volcano. very active volcanoes characteristically eject red-hot rocks and lava rather than this?
|
[
"greenhouse gases",
"carbon and smog",
"magma",
"smoke and ash"
] |
D
|
Example 3.5 Calculating Projectile Motion: Hot Rock Projectile Kilauea in Hawaii is the world’s most continuously active volcano. Very active volcanoes characteristically eject red-hot rocks and lava rather than smoke and ash. Suppose a large rock is ejected from the volcano with a speed of 25.0 m/s and at an angle 35.0º above the horizontal, as shown in Figure 3.40. The rock strikes the side of the volcano at an altitude 20.0 m lower than its starting point. (a) Calculate the time it takes the rock to follow this path. (b) What are the magnitude and direction of the rock’s velocity at impact?.
NIMS images revealed fourteen active volcanoes in a region thought to contain just four. Images of Loki Patera showed that in the four and half months between I24 and I27, some 10,000 square kilometers (3,900 sq mi) had been covered in fresh lava.
An active volcano is a volcano which is either erupting or is likely to erupt in the future. An active volcano which is not currently erupting is known as a dormant volcano.
After a phase of inactivity, Geysir started erupting again after a series of earthquakes in 2000. Geysir has since grown quieter and does not erupt often.With the widespread availability of geothermal power and the harnessing of many rivers and waterfalls for hydroelectricity, most residents have access to inexpensive hot water, heating, and electricity. The island is composed primarily of basalt, a low-silica lava associated with effusive volcanism as has occurred also in Hawaii.
Up to 400 such volcanoes are predicted to exist based on these observations. Io's volcanism makes the satellite one of only four known currently volcanically active worlds in the Solar System (the other three being Earth, Saturn's moon Enceladus, and Neptune's moon Triton).
Mount Erebus, in Antarctica, has maintained a lava lake since at least 1972. Mount Merapi Whakaari / White Island, has been in a continuous state of releasing volcanic gas since before European observation in 1769. Ol Doinyo Lengai Ambrym Arenal Volcano Pacaya Klyuchevskaya Sopka Sheveluch
|
When a meteoroid reaches earth, what is the remaining object called?
|
[
"comet",
"meteorite",
"meteor",
"orbit"
] |
B
|
Meteoroids are smaller than asteroids, ranging from the size of boulders to the size of sand grains. When meteoroids enter Earth’s atmosphere, they vaporize, creating a trail of glowing gas called a meteor. If any of the meteoroid reaches Earth, the remaining object is called a meteorite.
There are several videos of the meteoroid on YouTube. The object split into multiple pieces before widespread impact. The meteoroid entered the atmosphere at approximately 14 kilometres per second and is estimated to have been about the size of a desk and have had a mass of approximately 10 tonnes.The village of Marsden, Saskatchewan became a hub of activity for meteorite hunters, being just south of the estimated 20 square kilometre debris field.
3–6 m – approximate diameter of 2003 SQ222, a meteoroid 4.1 m – diameter of 2008 TC3, a small asteroid that flew into the Earth's atmosphere on 7 October 2008
The Orionids meteor shower is produced by Halley's Comet, which was named after the astronomer Edmund Halley and last passed through the inner Solar System in 1986 on its 75- to 76-year orbit. When the comet passes through the Solar System, the Sun sublimates some of the ice, allowing rock particles to break away from the comet. These particles continue on the comet's trajectory and appear as meteors ("falling stars") when they pass through Earth's upper atmosphere. Halley's comet is also responsible for creating the Eta Aquariids, which occur each May. * This meteor shower may give double peaks as well as plateaus, and time periods of flat maxima lasting several days.
It is the largest recorded object to have encountered the Earth since the 1908 Tunguska event. The meteor is estimated to have an initial diameter of 17–20 metres and a mass of roughly 10,000 tonnes. On 16 October 2013, a team from Ural Federal University led by Victor Grokhovsky recovered a large fragment of the meteor from the bottom of Russia's Lake Chebarkul, about 80 km west of the city.On 1 January 2014, a 3-meter (10 foot) asteroid, 2014 AA was discovered by the Mount Lemmon Survey and observed over the next hour, and was soon found to be on a collision course with Earth.
This definition corrects for the greater distance between an observer and a meteor near the horizon. For example, a meteor of magnitude −1 at 5 degrees above the horizon would be classified as a fireball because, if the observer had been directly below the meteor, it would have appeared as magnitude −6.Fireballs reaching apparent magnitude −14 or brighter are called bolides. The IAU has no official definition of "bolide", and generally considers the term synonymous with "fireball".
|
What kind of a reaction occurs when a substance reacts quickly with oxygen?
|
[
"invention reaction",
"combustion reaction",
"Fluid Reaction",
"nitrogen reaction"
] |
B
|
A combustion reaction occurs when a substance reacts quickly with oxygen (O 2 ). For example, in the Figure below , charcoal is combining with oxygen. Combustion is commonly called burning, and the substance that burns is usually referred to as fuel. The products of a complete combustion reaction include carbon dioxide (CO 2 ) and water vapor (H 2 O). The reaction typically gives off heat and light as well. The general equation for a complete combustion reaction is:.
This presents an additional barrier to the reaction. It also means molecular oxygen is relatively unreactive at room temperature except in the presence of a catalytic heavy atom such as iron or copper. Combustion consists of various radical chain reactions that the singlet radical can initiate.
This excited state then decomposes to species such as hydroxyl radicals (HO. ), hydrogen atoms (H.) and oxygen atoms (O.).
In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperature and concentrations present within a cell. The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays and reactions between elementary particles, as described by quantum field theory.
The net-reaction of all light-dependent reactions in oxygenic photosynthesis is: 2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2 H+ + 2NADPH + 3ATPPSI and PSII are light-harvesting complexes. If a special pigment molecule in a photosynthetic reaction center absorbs a photon, an electron in this pigment attains the excited state and then is transferred to another molecule in the reaction center. This reaction, called photoinduced charge separation, is the start of the electron flow and transforms light energy into chemical forms.
46 fs – the swiftest chemical reaction known (radiolysis of water leads to the formation of a H2O+ ion, which rapidly reacts to become hydronium (H3O+) and a short lived hydroxyl radical (•OH)) 200 fs – the average chemical reaction, such as the reaction of pigments in an eye to light 300 fs – the duration of a vibration of the atoms in an iodine molecule
|
Organisms categorized by what species descriptor demonstrate a version of allopatric speciation and have limited regions of overlap with one another, but where they overlap they interbreed successfully?.
|
[
"surface species",
"fitting species",
"species complex",
"ring species"
] |
D
|
Ring species Ring species demonstrate a version of allopatric speciation. Imagine populations of the species A. Over the geographic range of A there exist a number of subpopulations. These subpopulations (A1 to A5) and (Aa to Ae) have limited regions of overlap with one another but where they overlap they interbreed successfully. But populations A5 and Ae no longer interbreed successfully – are these populations separate species? In this case, there is no clear-cut answer, but it is likely that in the link between the various populations will be broken and one or more species may form in the future. Consider the black bear Ursus americanus. Originally distributed across all of North America, its distribution is now much more fragmented. Isolated populations are free to adapt to their own particular environments and migration between populations is limited. Clearly the environment in Florida is different from that in Mexico, Alaska, or Newfoundland. Different environments will favor different adaptations. If, over time, these populations were to come back into contact with one another, they might or might not be able to interbreed successfully - reproductive isolation may occur and one species may become many.
Further concepts developed by Barton and Hewitt in studying 170 hybrid zones, suggested that parapatric speciation can result from the same components that cause allopatric speciation. Called para-allopatric speciation, populations begin diverging parapatrically, fully speciating only after allopatry.
As allopatric speciation is widely accepted as a common mode of speciation, the scientific literature is abundant with studies documenting its existence. The biologist Ernst Mayr was the first to summarize the contemporary literature of the time in 1942 and 1963.: 91 Many of the examples he set forth remain conclusive; however, modern research supports geographic speciation with molecular phylogenetics—adding a level of robustness unavailable to early researchers. : 91 The most recent thorough treatment of allopatric speciation (and speciation research in general) is Jerry Coyne and H. Allen Orr's 2004 publication Speciation.
In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are. Species are reproductively isolated by strong barriers to hybridization, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo.
This gives rise to the potential for genetic incompatibilities to evolve. These incompatibilities cause reproductive isolation, giving rise to—sometimes rapid—speciation events. : 105 Furthermore, two important predictions are invoked, namely that geological or climatic changes cause populations to become locally fragmented (or regionally when considering allopatric speciation), and that an isolated population's reproductive traits evolve enough as to prevent interbreeding upon potential secondary contact.The peripatric model results in, what have been called, progenitor-derivative species pairs, whereby the derivative species (the peripherally isolated population)—geographically and genetically isolated from the progenitor species—diverges.
A negative value of Y {\displaystyle Y} denotes negative assortive mating, a positive value denotes positive assortive mating (i. e. expressing reproductive isolation), and a null value (of zero) means the populations are experiencing random mating.The experimental evidence has solidly established the fact that reproductive isolation evolves as a by-product of selection. : 90 Reproductive isolation has been shown to arise from pleiotropy (i.e. indirect selection acting on genes that code for more than one trait)—what has been referred to as genetic hitchhiking. Limitations and controversies exist relating to whether laboratory experiments can accurately reflect the long-scale process of allopatric speciation that occurs in nature.
|
Alpha emission is a type of what?
|
[
"radiation",
"radioactivity",
"heat",
"light"
] |
B
|
One type of radioactivity is alpha emission. What is an alpha particle? What happens to an alpha particle after it is emitted from an unstable nucleus?.
H-alpha (Hα) is a deep-red visible spectral line of the hydrogen atom with a wavelength of 656.28 nm in air and 656.46 nm in vacuum. It is the first spectral line in the Balmer series and is emitted when an electron falls from a hydrogen atom's third- to second-lowest energy level. H-alpha has applications in astronomy where its emission can be observed from emission nebulae and from features in the Sun's atmosphere, including solar prominences and the chromosphere.
Alpha process elements (or alpha elements) are so-called since their most abundant isotopes are integer multiples of four – the mass of the helium nucleus (the alpha particle). These isotopes are called alpha nuclides. The stable alpha elements are: C, O, Ne, Mg, Si, and S. The elements Ar and Ca are "observationally stable".
The instrument was designed to detect the energy of all three components of the return radiation, making it possible to identify the atoms present and their quantities in a few tens of micrometers below the surface of the analyzed sample. The detection process was rather slow; each measurement could take up to ten hours.Sensitivity and selectivity depends on a channel; alpha backscattering has high sensitivity for light elements like carbon and oxygen, proton emission is mainly sensitive to sodium, magnesium, aluminium, silicon, sulfur, and X-ray emission is more sensitive to heavier elements sodium to iron and beyond. Combining all three measurements makes APXS sensitive to all elements with the exception of hydrogen that is present at concentration levels above a fraction of one percent.
Neutron emission is a mode of radioactive decay in which one or more neutrons are ejected from a nucleus. It occurs in the most neutron-rich/proton-deficient nuclides, and also from excited states of other nuclides as in photoneutron emission and beta-delayed neutron emission. As only a neutron is lost by this process the number of protons remains unchanged, and an atom does not become an atom of a different element, but a different isotope of the same element. Neutrons are also produced in the spontaneous and induced fission of certain heavy nuclides.
The usual design is based on a combination of beryllium-9 and polonium-210, separated until activation, then placed in intimate contact by the shock wave. Polonium-208 and actinium-227 were also considered as alpha sources. The isotope used must have strong alpha emissions and weak gamma emissions, as gamma photons can also knock neutrons loose and cannot be so efficiently shielded as alpha particles. Several variants were developed, differing by the dimensions and mechanical configuration of the system ensuring proper mixing of the metals.
|
What is the stored food in a seed called?
|
[
"pollin",
"endosperm",
"membrane",
"larval"
] |
B
|
The stored food in a seed is called endosperm . It nourishes the embryo until it can start making food on its own.
The seeds are eaten by chipmunks, mice, and squirrels. Rabbits and voles eat the bark, sometimes girdling young trees. The leaves serve as food for caterpillars of various Lepidoptera (see Lepidoptera which feed on Tilia).
Seed germination is a process by which a seed embryo develops into a seedling. It involves the reactivation of the metabolic pathways that lead to growth and the emergence of the radicle or seed root and plumule or shoot. The emergence of the seedling above the soil surface is the next phase of the plant's growth and is called seedling establishment.Three fundamental conditions must exist before germination can occur. (1) The embryo must be alive, called seed viability.
The fruit is a nut with four 1 cm (1⁄2 in) barbed spines. Seeds can remain viable up to 12 years, although most germinate within the first two years. The plant spreads by the rosettes and fruits detaching from the stem and floating to another area on currents or by fruits clinging to objects, and animals.
When the seed imbibes water, hydrolytic enzymes are activated which break down these stored food resources into metabolically useful chemicals. After the seedling emerges from the seed coat and starts growing roots and leaves, the seedling's food reserves are typically exhausted; at this point photosynthesis provides the energy needed for continued growth and the seedling now requires a continuous supply of water, nutrients, and light. Oxygen is required by the germinating seed for metabolism.
Some specimens cannot be compressed, degrade when dried, or require other techniques for preservation and storage. Large seeds or fruits may be stored in boxes without compression. Aquatic plants and delicate plants may be stored in a liquid preservative. Cacti may be stored in ethanol.
|
Zinc is more easily oxidized than iron because zinc has a lower reduction potential. since zinc has a lower reduction potential, it is a more what?
|
[
"much metal",
"Trap metal",
"active metal",
"usually metal"
] |
C
|
One way to keep iron from corroding is to keep it painted. The layer of paint prevents the water and oxygen necessary for rust formation from coming into contact with the iron. As long as the paint remains intact, the iron is protected from corrosion. Other strategies include alloying the iron with other metals. For example, stainless steel is mostly iron with a bit of chromium. The chromium tends to collect near the surface, where it forms an oxide layer that protects the iron. Zinc-plated or galvanized iron uses a different strategy. Zinc is more easily oxidized than iron because zinc has a lower reduction potential. Since zinc has a lower reduction potential, it is a more active metal. Thus, even if the zinc coating is scratched, the zinc will still oxidize before the iron. This suggests that this approach should work with other active metals. Another important way to protect metal is to make it the cathode in a galvanic cell. This is cathodic protection and can be used for metals other than just iron. For example, the rusting of underground iron storage tanks and pipes can be prevented or greatly reduced by connecting them to a more active metal such as zinc or magnesium (Figure 17.18). This is also used to protect the metal parts in water heaters. The more active metals (lower reduction potential) are called sacrificial anodes because as they get used up as they corrode (oxidize) at the anode. The metal being protected serves as the cathode, and so does not oxidize (corrode). When the anodes are properly monitored and periodically replaced, the useful lifetime of the iron storage tank can be greatly extended.
Oxidation and reduction reactions are not common in organic chemistry as few organic molecules can act as oxidizing or reducing agents. Iron(II), on the other hand, can easily be oxidized to iron(III). This functionality is used in cytochromes, which function as electron-transfer vectors. The presence of the metal ion allows metalloenzymes to perform functions such as redox reactions that cannot easily be performed by the limited set of functional groups found in amino acids.
Compounds with zinc in the oxidation state +1 are extremely rare. The compounds have the formula RZn2R and they contain a Zn — Zn bond analogous to the metal-metal bond in mercury(I) ion, Hg22+. In this respect zinc is similar to magnesium where low-valent compounds containing a Mg — Mg bond have been characterised.
In the filtration process, zinc acts as an anode and copper as a cathode in an electrolytic cell. Ionic contaminants are removed by electron exchange (a redox reaction), in which they are converted to a more physiologically inert form. This redox reaction generates an electric potential of about 300mV, which may be responsible for the partial antimicrobial effect, along with hydroxyl radicals that form during the process.
The following table provides the reduction potentials of the indicated reducing agent at 25 °C. For example, among sodium (Na) metal, chromium (Cr) metal, cuprous (Cu+) ion and chloride (Cl−) ion, it is Na metal that is the strongest reducing agent while Cl− ion is the weakest; said differently, Na+ ion is the weakest oxidizing agent in this list while Cl2 molecule is the strongest. Some elements and compounds can be both reducing or oxidizing agents.
Dissimilatory metal-reducing microorganisms are a group of microorganisms (both bacteria and archaea) that can perform anaerobic respiration utilizing a metal as terminal electron acceptor rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration. The most common metals used for this end are iron and manganese , which are reduced to Fe(II) and Mn(II) respectively, and most microorganisms that reduce Fe(III) can reduce Mn(IV) as well. But other metals and metalloids are also used as terminal electron acceptors, such as vanadium , chromium , molybdenum , cobalt , palladium , gold , and mercury .
|
What is controlled by both genes and experiences in a given envionment?
|
[
"reflexes",
"animal behaviors",
"instincts",
"learned behaviors"
] |
B
|
Most animal behaviors are controlled by both genes and experiences in a given environment.
Genes provide numerous options for varying cells to be expressed; however, the environment determines which of these are activated. Many studies have noted this relationship in varying ways in which our bodies can develop, but the interaction between genes and the shaping of our minds and personality is also relevant to this biological relationship.DNA-environment interactions are important in the development of personality because this relationship determines what part of the DNA code is actually made into proteins that will become part of an individual. While different choices are made available by the genome, in the end, the environment is the ultimate determinant of what becomes activated.
Genetics influence individuals as they select their environment.
Regulation of gene expression is the control of the amount and timing of appearance of the functional product of a gene. Control of expression is vital to allow a cell to produce the gene products it needs when it needs them; in turn, this gives cells the flexibility to adapt to a variable environment, external signals, damage to the cell, and other stimuli. More generally, gene regulation gives the cell control over all structure and function, and is the basis for cellular differentiation, morphogenesis and the versatility and adaptability of any organism. Numerous terms are used to describe types of genes depending on how they are regulated; these include: A constitutive gene is a gene that is transcribed continually as opposed to a facultative gene, which is only transcribed when needed.
Another condition that permits the disassociation of genes and environment is adoption. In one kind of adoption study, biological siblings reared together (who share the same family environment and half their genes) are compared to adoptive siblings (who share their family environment but none of their genes). In many cases, it has been found that genes make a substantial contribution, including psychological traits such as intelligence and personality.
Some critics view evolutionary psychology as a form of genetic reductionism and genetic determinism, a common critique being that evolutionary psychology does not address the complexity of individual development and experience and fails to explain the influence of genes on behavior in individual cases. Evolutionary psychologists respond that they are working within a nature-nurture interactionist framework that acknowledges that many psychological adaptations are facultative (sensitive to environmental variations during individual development). The discipline is generally not focused on proximate analyses of behavior, but rather its focus is on the study of distal/ultimate causality (the evolution of psychological adaptations). The field of behavioral genetics is focused on the study of the proximate influence of genes on behavior.
|
What tells you how much of the food you should eat to get the nutrients listed on the label?
|
[
"serving size",
"regular size",
"scoop size",
"longer size"
] |
A
|
The information listed at the right of the label tells you what to look for. At the top of the label, look for the serving size. The serving size tells you how much of the food you should eat to get the nutrients listed on the label. A cup of food from the label pictured below is a serving. The calories in one serving are listed next. In this food, there are 250 calories per serving.
For vitamin C, vitamin D, vitamin E, vitamin K, calcium, phosphorus, magnesium, and manganese, the current highest RDAs are up to 50% higher than the older Daily Values used in labeling, whereas for other nutrients the recommended needs have gone down. A side-by-side table of the old and new adult Daily Values is provided at Reference Daily Intake. As of October 2010, the only micronutrients that are required to be included on all labels are vitamin A, vitamin C, calcium, and iron.
(eds.). Nutrition: A functional Approach.
Consumer advisories for dietary nutrient intakes, such as the United States Dietary Reference Intake, are based on deficiency outcomes and provide macronutrient and micronutrient guides for both lower and upper limits of intake. In many countries, macronutrients and micronutrients in significant content are required by regulations to be displayed on food product labels. Nutrients in larger quantities than the body needs may have harmful effects. Edible plants also contain thousands of compounds generally called phytochemicals which have unknown effects on disease or health, including a diverse class with non-nutrient status called polyphenols, which remain poorly understood as of 2017.
For US food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of daily value. For biotin labeling purposes 100% of the daily value was 300 μg/day, but as of May 27, 2016, it was revised to 30 μg/day to bring it into an agreement with the adequate intake. Compliance with the updated labeling regulations was required by January 1, 2020, for manufacturers with US$10 million or more in annual food sales, and by January 1, 2021, for manufacturers with lower volume food sales. A table of the old and new adult daily values is provided at Reference Daily Intake.
Salt 0.2g per 100g, Sodium 80 mg per 100g. Saturated fat 13g per 100g. Protein 4.7g per 100g. Fibre 1.5g per 100g.
|
What are used to write nuclear equations for radioactive decay?
|
[
"trigonometric symbols",
"critical symbols",
"radioactive symbols",
"nuclear symbols"
] |
D
|
Nuclear symbols are used to write nuclear equations for radioactive decay. Let’s consider the example of the beta-minus decay of thorium-234 to protactinium-234. This reaction is represented by the equation:.
The kinetics of the reactor is described by the balance equations of neutrons and nuclei (fissile, fission products).
The valley of stability can be helpful in interpreting and understanding properties of nuclear decay processes such as decay chains and nuclear fission. Radioactive decay often proceeds via a sequence of steps known as a decay chain. For example, 238U decays to 234Th which decays to 234mPa and so on, eventually reaching 206Pb: U 92 238 → 4.5 × 10 9 y α Th 90 234 → 24 d β − Pa 91 234 m → 1 min β − U 92 234 → 2.4 × 10 5 y α Th 90 230 → 7.7 × 10 4 y α Ra 88 226 → 1600 y α Rn 86 222 → 3.8 d α Po 84 218 → 3 min α Pb 82 214 → 27 min β − Bi 83 214 → 20 min β − Po 84 214 → 164 μ s α Pb 82 210 → 22 y β − Bi 83 210 → 5 d β − Po 84 210 → 138 d α Pb 82 206 {\displaystyle {\begin{array}{l}{}\\{\ce {^{238}_{92}U->{^{234}_{90}Th}->{^{234\!m}_{91}Pa}}}{\ce {->}}{\ce {^{234}_{92}U->{^{230}_{90}Th}->}}\\{\ce {^{226}_{88}Ra->{^{222}_{86}Rn}->{^{218}_{84}Po}->{^{214}_{82}Pb}->{^{214}_{83}Bi}->}}\\{\ce {^{214}_{84}Po->{^{210}_{82}Pb}->{^{210}_{83}Bi}->{^{210}_{84}Po}->{^{206}_{82}Pb}}}\\{}\end{array}}} With each step of this sequence of reactions, energy is released and the decay products move further down the valley of stability towards the line of beta stability.
The other common way for isotopes with a high neutron to proton ratio (n/p) to decay is beta decay, in which the nuclide changes elemental identity while keeping the same mass number and lowering its n/p ratio. For some isotopes with a relatively low n/p ratio, there is an inverse beta decay, by which a proton is transformed into a neutron, thus moving towards a stable isotope; however, since fission almost always produces products which are neutron heavy, positron emission or electron capture are rare compared to electron emission. There are many relatively short beta decay chains, at least two (a heavy, beta decay and a light, positron decay) for every discrete weight up to around 207 and some beyond, but for the higher mass elements (isotopes heavier than lead) there are only four pathways which encompass all decay chains.
An example of this kind of a nuclear reaction occurs in the production of cobalt-60 within a nuclear reactor: The cobalt-60 then decays by the emission of a beta particle plus gamma rays into nickel-60. This reaction has a half-life of about 5.27 years, and due to the availability of cobalt-59 (100% of its natural abundance), this neutron bombarded isotope of cobalt is a valuable source of nuclear radiation (namely gamma radiation) for radiotherapy. 5927Co + 10n → 6027CoIn other cases, and depending on the kinetic energy of the neutron, the capture of a neutron can cause nuclear fission—the splitting of the atomic nucleus into two smaller nuclei. If the fission requires an input of energy, that comes from the kinetic energy of the neutron.
He coins the terms alpha and beta rays in 1899 to describe the two distinct types of radiation emitted by thorium and uranium salts. Rutherford is joined at McGill University in 1900 by Frederick Soddy and together they discover nuclear transmutation when they find in 1902 that radioactive thorium is converting itself into radium through a process of nuclear decay and a gas (later found to be 42He); they report their interpretation of radioactivity in 1903. Rutherford becomes known as the "father of nuclear physics" with his nuclear atom model of 1911.
|
What is controlled by regulatory proteins that bind to regulatory elements on dna?
|
[
"amino acids",
"mRNA",
"gene transcription",
"substance transcription"
] |
C
|
Gene transcription is controlled by regulatory proteins that bind to regulatory elements on DNA. The proteins usually either activate or repress transcription.
Regulatory elements are sites that control the transcription of a nearby gene. They are almost always sequences where transcription factors bind to DNA and these transcription factors can either activate transcription (activators) or repress transcription (repressors). Regulatory elements were discovered in the 1960s and their general characteristics were worked out in the 1970s by studying specific transcription factors in bacteria and bacteriophage.Promoters and regulatory sequences represent an abundant class of noncoding DNA but they mostly consist of a collection of relatively short sequences so they don't take up a very large fraction of the genome.
One way that genes are regulated is through the remodeling of chromatin. Chromatin is the complex of DNA and the histone proteins with which it associates. If the way that DNA is wrapped around the histones changes, gene expression can change as well.
All the functions of DNA depend on interactions with proteins. These protein interactions can be non-specific, or the protein can bind specifically to a single DNA sequence. Enzymes can also bind to DNA and of these, the polymerases that copy the DNA base sequence in transcription and DNA replication are particularly important.
It is common in biology for important processes to have multiple layers of regulation and control. This is also true with transcription factors: Not only do transcription factors control the rates of transcription to regulate the amounts of gene products (RNA and protein) available to the cell but transcription factors themselves are regulated (often by other transcription factors). Below is a brief synopsis of some of the ways that the activity of transcription factors can be regulated:
Eukaryotes have a much larger genome and thus have different methods of gene regulation than in prokaryotes. All cells in a eukaryotic organism have the same DNA but are specified through differential gene expression, a phenomenon known as genetic totipotency. However, in order for a cell to express the genes for proper functioning, the genes must be closely regulated to express the correct properties. Genes in eukaryotes are controlled on the transcriptional, post-transcriptional, translational, and post-translational levels. On the transcriptional level, gene expression is regulated by altering transcription rates. Genes that encode proteins include exons which will encode the polypeptides, introns that are removed from mRNA before the translation of proteins, a transcriptional start site in which RNA polymerase binds, and a promoter.
|
Boron only occurs naturally in compounds with what element?
|
[
"oxygen",
"helium",
"nitrogen",
"carbon"
] |
A
|
Occurrence, Preparation, and Compounds of Boron and Silicon Boron constitutes less than 0.001% by weight of the earth’s crust. In nature, it only occurs in compounds with oxygen. Boron is widely distributed in volcanic regions as boric acid, B(OH)3, and in dry lake regions, including the desert areas of California, as borates and salts of boron oxyacids, such as borax, Na2B4O7⋅10H2O. Elemental boron is chemically inert at room temperature, reacting with only fluorine and oxygen to form boron trifluoride, BF3, and boric oxide, B2O3, respectively. At higher temperatures, boron reacts with all nonmetals, except tellurium and the noble gases, and with nearly all metals; it oxidizes to B2O3 when heated with concentrated nitric or sulfuric acid. Boron does not react with nonoxidizing acids. Many boron compounds react readily with water to give boric acid, B(OH)3 (sometimes written as H3BO3). Reduction of boric oxide with magnesium powder forms boron (95–98.5% pure) as a brown, amorphous powder: B 2 O 3(s) + 3Mg(s) ⟶ 2B(s) + 3MgO(s) An amorphous substance is a material that appears to be a solid, but does not have a long-range order like a true solid. Treatment with hydrochloric acid removes the magnesium oxide. Further purification of the boron begins with conversion of the impure boron into boron trichloride. The next step is to heat a mixture of boron trichloride and hydrogen: 1500 °C.
Boron is the lightest element having an electron in a p-orbital in its ground state. Unlike most other p-elements, it rarely obeys the octet rule and usually places only six electrons (in three molecular orbitals) onto its valence shell. Boron is the prototype for the boron group (the IUPAC group 13), although the other members of this group are metals and more typical p-elements (only aluminium to some extent shares boron's aversion to the octet rule).
Although a very small amount of carbon (less than 2 wt%!) plays an important role in the phase stability, carbon does not have its own sites but shares with boron two interstitial sites B/C15 and B/C16.
In 1995, the first report on attempted isolation of the element was unsuccessful, prompting new theoretical studies to investigate how best to investigate bohrium (using its lighter homologs technetium and rhenium for comparison) and removing unwanted contaminating elements such as the trivalent actinides, the group 5 elements, and polonium.In 2000, it was confirmed that although relativistic effects are important, bohrium behaves like a typical group 7 element. A team at the Paul Scherrer Institute (PSI) conducted a chemistry reaction using six atoms of 267Bh produced in the reaction between 249Bk and 22Ne ions. The resulting atoms were thermalised and reacted with a HCl/O2 mixture to form a volatile oxychloride.
The metalloids tend to be found in forms combined with oxygen, sulfur, or (in the case of tellurium) gold or silver. Boron is found in boron-oxygen borate minerals, including in volcanic spring waters. Silicon occurs in the silicon-oxygen mineral silica (sand).
This property is used to determine the presence of boron in qualitative analysis. Borate esters form spontaneously when treated with diols such as sugars and the reaction with mannitol forms the basis of a titrimetric analytical method for boric acid. Metaborate esters show considerable Lewis acidity and can initiate epoxide polymerization reactions.
|
What organ systems link exchange surfaces with cells throughout the body?
|
[
"vascular",
"circulatory",
"pulmonary",
"nervous"
] |
B
|
42.1 Circulatory systems link exchange surfaces with cells throughout the body.
Concentration differential between tissues. Exchange surface. Presence of natural barriers.
However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column. To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell.
Cells within tissues and organs must be anchored to one another and attached to components of the extracellular matrix. Cells have developed several types of junctional complexes to serve these functions, and in each case, anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighboring cells as well as to proteins in the extracellular matrix.Three types of anchoring junctions are observed, and differ from one another in the cytoskeletal protein anchor as well as the transmembrane linker protein that extends through the membrane: Anchoring-type junctions not only hold cells together but provide tissues with structural cohesion. These junctions are most abundant in tissues that are subject to constant mechanical stress such as skin and heart.
The motion of the flagella sucks water through passages in the "cobweb" and expels it via the open ends of the bell-shaped chambers.Some types of cells have a single nucleus and membrane each but are connected to other single-nucleus cells and to the main syncytium by "bridges" made of cytoplasm. The sclerocytes that build spicules have multiple nuclei, and in glass sponge larvae they are connected to other tissues by cytoplasm bridges; such connections between sclerocytes have not so far been found in adults, but this may simply reflect the difficulty of investigating such small-scale features. The bridges are controlled by "plugged junctions" that apparently permit some substances to pass while blocking others.
The endodermal cells primarily generate the lining and glands of the digestive tube
|
What occurs when the immune system attacks a harmless substance that enters the body from the outside?
|
[
"panic attack",
"nausea",
"allergy",
"plague"
] |
C
|
An allergy occurs when the immune system attacks a harmless substance that enters the body from the outside. A substance that causes an allergy is called an allergen. It is the immune system, not the allergen, that causes the symptoms of an allergy.
The organism enters directly through the breakdown of mechanical defense barriers such as mucosa or skin. Conditions which lead to the development of an immunocompromised state make the patient more susceptible to ecthyma gangrenosum and sepsis. In case of sepsis, the bacteria reaches the skin via the bloodstream.
The immune system recognizes foreign pathogens and eliminates them. This occurs in several phases. In the early inflammation phase, the pathogens are recognized by antibodies that are already present (innate or acquired through prior infection; see also cross-reactivity). Immune-system components (e.g. complement) are bound to the antibodies and kept near, in reserve to disable them via phagocytosis by scavenger cells (e.g. macrophages).
The innate immune system is made of non-specific defensive mechanisms against foreign cells inside the host including skin as a physical barrier to entry, activation of the complement cascade to identify foreign bacteria and activate necessary cell responses, and white blood cells that remove foreign substances. The adaptive immune system, or acquired immune system, is a pathogen-specific immune response that is carried out by lymphocytes through antigen presentation on MHC molecules to distinguish between self and non-self antigens.
Immunosenescence occurs over time where the immune system undergoes changes that may impact both the innate and adaptive immune systems. These alterations may lead to increased immunoreactivity to intrinsic and extrinsic stimuli that can cause the body to become more sensitive and reactive. This may result in the form of an itch when exposed to stimuli that the body was not reactive to in the past. The immune system is responsible for a myriad of activities to defend the body from foreign substances via various endogenous and exogenous pathways.
Phagocytosis is the process of uptake of microbes and particles followed by digestion and destruction of this material. Monocytes can perform phagocytosis using intermediary (opsonising) proteins such as antibodies or complement that coat the pathogen, as well as by binding to the microbe directly via pattern recognition receptors that recognize pathogens. Monocytes are also capable of killing infected host cells via antibody-dependent cell-mediated cytotoxicity. Vacuolization may be present in a cell that has recently phagocytized foreign matter.
|
Fertilization is the union of a sperm and egg, resulting in the formation of what?
|
[
"a cytoplasm",
"a zygote",
"a nuclei",
"a bacteriophage"
] |
B
|
Fertilization is the union of a sperm and egg, resulting in the formation of a zygote.
Through an interplay of hormones that includes follicle stimulating hormone that stimulates folliculogenesis and oogenesis creates a mature egg cell, the female gamete. Fertilization is the event where the egg cell fuses with the male gamete, spermatozoon. After the point of fertilization, the fused product of the female and male gamete is referred to as a zygote or fertilized egg. The fusion of female and male gametes usually occurs following the act of sexual intercourse.
At this point the end of the pollen tube bursts and releases the two sperm cells, one of which makes its way to an egg, while also losing its cell membrane and much of its protoplasm. The sperm's nucleus then fuses with the egg's nucleus, resulting in the formation of a zygote, a diploid (two copies of each chromosome) cell.Whereas in fertilization only plasmogamy, or the fusion of the whole sex cells, results, in Angiosperms (flowering plants) a process known as double fertilization, which involves both karyogamy and plasmogamy, occurs. In double fertilization the second sperm cell subsequently also enters the synergid and fuses with the two polar nuclei of the central cell. Since all three nuclei are haploid, they result in a large endosperm nucleus which is triploid.
Upon fertilization, the diploid egg will give rise to the embryo, and a seed is produced. The female cone then opens, releasing the seeds which grow to a young seedling. To fertilize the ovum, the male cone releases pollen that is carried in the wind to the female cone.
The transfer of pollen (the male gametophytes) to the female stigmas occurs is called pollination. After pollination occurs, the pollen grain germinates to form a pollen tube that grows through the carpel's style and transports male nuclei to the ovule to fertilize the egg cell and central cell within the female gametophyte in a process termed double fertilization. The resulting zygote develops into an embryo, while the triploid endosperm (one sperm cell plus a binucleate female cell) and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The fertilized ovules develop into seeds within a fruit formed from the ovary. When the seeds are ripe they may be dispersed together with the fruit or freed from it by various means to germinate and grow into the next generation.
Released from the binucleate sperm cell are two sperm nuclei which then join with free egg nuclei to produce two viable zygotes, a homologous characteristic between families Ephedra and Gnetum. In both families, the second fertilization event produces an additional diploid embryo. This supernumerary embryo is later aborted, leading to the synthesis of only one mature embryo.
|
The plants alternation between haploid and diploud generations allow it to do what?
|
[
"reproduce asexually and simultaneously",
"reproduce asexually and sexually",
"reproduce sexually and autonomously",
"reproduce asexually and biologically"
] |
B
|
All plants have a characteristic life cycle that includes alternation of generations . Plants alternate between haploid and diploid generations. Alternation of generations allows for both asexual and sexual reproduction. Asexual reproduction with spores produces haploid individuals called gametophytes . Sexual reproduction with gametes and fertilization produces diploid individuals called sporophytes . A typical plant’s life cycle is diagrammed in Figure below .
Diplospory, a type of Agamospermy, occurs during the development of female gametophyte in the ovule and hence reduction division does not take place in the Megaspore mother cell. The diploid egg is unfertilized and forms the embryo. Hence daughter plants are exactly clones of the mother. The species uses C4 carbon fixation. It is dioecious, meaning male and female flowers are produced on separate individuals.
The diplobiontic forms, which evolved from haplobiontic ancestors, have both a multicellular haploid generation and a multicellular diploid generation. Here the zygote divides repeatedly by mitosis and grows into a multicellular diploid sporophyte. The sporophyte produces haploid spores by meiosis that germinate to produce a multicellular gametophyte.
Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis; the sporophyte generation is diploid and produces spores by meiosis. Polyploidy may occur due to abnormal cell division, either during mitosis, or more commonly from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm.
The sporophyte develops from the zygote produced when a haploid egg cell is fertilized by a haploid sperm and each sporophyte cell therefore has a double set of chromosomes, one set from each parent. All land plants, and most multicellular algae, have life cycles in which a multicellular diploid sporophyte phase alternates with a multicellular haploid gametophyte phase. In the seed plants, the largest groups of which are the gymnosperms and flowering plants (angiosperms), the sporophyte phase is more prominent than the gametophyte, and is the familiar green plant with its roots, stem, leaves and cones or flowers. In flowering plants the gametophytes are very reduced in size, and are represented by the germinated pollen and the embryo sac.
Although it is not the usual route of a microspore, this process is the most effective way of yielding haploid and double haploid plants through the use of male sex hormones. Under certain stressors such as heat or starvation, plants select for microspore embryogenesis. It was found that over 250 different species of angiosperms responded this way.
|
Most of the chemical reactions in the body are facilitated by what?
|
[
"proteins",
"vitamins",
"carbohydrates",
"enzymes"
] |
D
|
Enzymes are critical to the body’s healthy functioning. They assist, for example, with the breakdown of food and its conversion to energy. In fact, most of the chemical reactions in the body are facilitated by enzymes.
In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperature and concentrations present within a cell. The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays and reactions between elementary particles, as described by quantum field theory.
' is the process of absorption of vitamins, minerals, and other chemicals from food as part of the nutrition of an organism. In humans, this is always done with a chemical breakdown (enzymes and acids) and physical breakdown (oral mastication and stomach churning).chemical alteration of substances in the bloodstream by the liver or cellular secretions. Although a few similar compounds can be absorbed in digestion bio assimilation, the bioavailability of many compounds is dictated by this second process since both the liver and cellular secretions can be very specific in their metabolic action (see chirality). This second process is where the absorbed food reaches the cells via the liver.
There are five main ways that enzyme activity is controlled in the cell. : 30.1.1
In chemistry, reactivity is the impulse for which a chemical substance undergoes a chemical reaction, either by itself or with other materials, with an overall release of energy. Reactivity refers to: the chemical reactions of a single substance, the chemical reactions of two or more substances that interact with each other, the systematic study of sets of reactions of these two kinds, methodology that applies to the study of reactivity of chemicals of all kinds, experimental methods that are used to observe these processes theories to predict and to account for these processes.The chemical reactivity of a single substance (reactant) covers its behavior in which it: Decomposes Forms new substances by addition of atoms from another reactant or reactants Interacts with two or more other reactants to form two or more productsThe chemical reactivity of a substance can refer to the variety of circumstances (conditions that include temperature, pressure, presence of catalysts) in which it reacts, in combination with the: Variety of substances with which it reacts Equilibrium point of the reaction (i.e., the extent to which all of it reacts) Rate of the reactionThe term reactivity is related to the concepts of chemical stability and chemical compatibility.
For example, sulfur disrupts the production of methanol by poisoning the Cu/ZnO catalyst. Substances that increase reaction rate are called promoters. For example, the presence of alkali metals in ammonia synthesis increases the rate of N2 dissociation.The presence of poisons and promoters can alter the activation energy of the rate-limiting step and affect a catalyst's selectivity for the formation of certain products.
|
What is the termination of a pregnancy in progress called?
|
[
"contraception",
"miscarriage",
"delivery",
"abortion"
] |
D
|
Canady could not find this particular abortion practice named in any medical textbook, and therefore he and his aides named it. "Partial-birth abortion" was first used in the media on June 4, 1995, in a Washington Times article covering the bill. In the U.S., a federal statute defines "partial-birth abortion" as any abortion in which the life of the fetus is terminated after having been extracted from the mother's body to a point "past the navel " or "in the case of head-first presentation, the entire fetal head is outside the body of the mother" at the time the life is terminated.
A threatened miscarriage is any bleeding during the first half of pregnancy. At investigation it may be found that the fetus remains viable and the pregnancy continues without further problems.An anembryonic pregnancy (also called an "empty sac" or "blighted ovum") is a condition where the gestational sac develops normally, while the embryonic part of the pregnancy is either absent or stops growing very early. This accounts for approximately half of miscarriages. All other miscarriages are classified as embryonic miscarriages, meaning that there is an embryo present in the gestational sac.
The procedure is also used in multiple pregnancies when one of the fetuses has a serious and incurable disease, or in the case where one of the fetuses is outside the uterus, in which case it is called selective termination.The procedure generally takes two days; the first day for testing in order to select which fetuses to reduce, and the second day for the procedure itself, in which potassium chloride is injected into the heart of each selected fetus under the guidance of ultrasound imaging. Risks of the procedure include bleeding requiring transfusion, rupture of the uterus, retained placenta, infection, a miscarriage, and prelabor rupture of membranes. Each of these appears to be rare.Selective reduction was developed in the mid-1980s, as people in the field of assisted reproductive technology became aware of the risks that multiple pregnancies carried for the mother and for the fetuses.
Pregnancy is the development of an embryo or fetus inside the womb of a female for the rough duration of 9 months or 40 weeks from the last menstrual period until birth. It is divided into three trimesters, each lasting for about 3 months. The 1st trimester is when the developing embryo becomes a fetus, organs start to develop, limbs grow, and facial features appear. The 2nd and 3rd trimesters are marked by a significant amount of growth and functional development of the body.
Normally, it occurs spontaneously at full term either during or at the beginning of labor. A premature rupture of membranes (PROM) is a rupture of the amnion that occurs prior to the onset of labor. An artificial rupture of membranes (AROM), also known as an amniotomy, may be clinically performed using an amnihook or amnicot in order to induce or to accelerate labour.
|
Cutting down on the use of chemical fertilizers and preserving wetlands are ways to prevent what "unlivable" regions in bodies of water?
|
[
"inhabitable zones",
"hostile zones",
"fresh zones",
"dead zones"
] |
D
|
Cutting down on the use of chemical fertilizers is one way to prevent dead zones in bodies of water. Preserving wetlands is also important. Wetlands are habitats such as swamps, marshes, and bogs where the ground is soggy or covered with water much of the year. Wetlands slow down and filter runoff before it reaches bodies of water. Wetlands also provide breeding grounds for many different species of organisms.
Constructed wetlands located strategically on the landscape to process drainage effluent reduces sediment and nitrate loads to surface water.
Physical, chemical, and biological processes combine in wetlands to remove contaminants from wastewater. An understanding of these processes is fundamental not only to designing wetland systems but to understanding the fate of chemicals once they enter the wetland. Theoretically, wastewater treatment within a constructed wetland occurs as it passes through the wetland medium and the plant rhizosphere. A thin film around each root hair is aerobic due to the leakage of oxygen from the rhizomes, roots, and rootlets.
Contaminant remediation in aquifers. The decision problem is where to locate wells, and choose a pumping rate, to minimize the cost to prevent spread of a contaminant. The constraints are associated with the hydrogeological flows.Water allocation to improve wetlands. This optimization model recommends water allocation and invasive vegetation control to improve wetland habitat of priority bird species.
(August 1999). "Management of Eutrophication for Lakes Subject to Potentially Irreversible Change". Ecological Applications.
Despite policies mandating no net loss of habitat value and function, agencies have had difficulty ensuring that mitigation programs are managed. Wetland mitigation programs, for example, have in some cases been approved based on total numbers of acres rather than in terms of equivalence in ecological value or function. Merely assuming that the compensation involves a similar number of acres falls short of true equivalence unless the replacement ecological functions supplied by those acres are also the same.A challenge faced by regulatory agencies is giving correct economic or monetary value for ecological loss, even through the use of environmental assessment techniques. Although mitigation banks have to be located in the same watershed as the impact in order to be considered adequate compensation, mitigation banks are often located far from the actual site of impact. Therefore, it is difficult to retain the original value and function.
|
Which muscles allow your fingers to also make precise movements for actions?
|
[
"paired muscles",
"motoric muscles",
"intrinsic muscles",
"fine movement muscles"
] |
C
|
Intrinsic Muscles of the Hand The intrinsic muscles of the hand both originate and insert within it (Figure 11.28). These muscles allow your fingers to also make precise movements for actions, such as typing or writing. These muscles are divided into three groups. The thenar muscles are on the radial aspect of the palm. The hypothenar muscles are on the medial aspect of the palm, and the intermediate muscles are midpalmar. The thenar muscles include the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and the adductor pollicis. These muscles form the thenar eminence, the rounded contour of the base of the thumb, and all act on the thumb. The movements of the thumb play an integral role in most precise movements of the hand. The hypothenar muscles include the abductor digiti minimi, flexor digiti minimi brevis, and the opponens digiti minimi. These muscles form the hypothenar eminence, the rounded contour of the little finger, and as such, they all act on the little finger. Finally, the intermediate muscles act on all the fingers and include the lumbrical, the palmar interossei, and the dorsal interossei.
It has been shown that tactile afferents from the glabrous skin of the hand exert profound effects on hand and finger muscles in the subconscious control of grip force whenever we lift and manipulate objects. The friction between skin and object surface is extracted as soon as your fingers close around the object and contraction force of the muscles gripping the object is adjusted accordingly. Moreover, any tendency to slipping is monitored by tactile afferents and gives rise to swift reflexes resulting in subconscious adjustments of motor output. Many forms of dexterous handling of objects include successive phases of different motor activity. It has been shown that tactile sense organs in the glabrous skin are involved in timely linking the separated phases to a purposeful motor act.
Moving hand across torso in wave motion: "Current" Divers sometimes invent local signals for local situations, often to point out local wildlife. For example: I see a hammerhead shark: Both fists against sides of head I see a lobster: Fist with index and middle finger pointed out horizontally and alternately waggling up and down I see an octopus: Back of hand or wrist covering mouth, all fingers pointing outward from mouth and wiggling I see a shark: Hand flat, fingers vertical, thumb against forehead or chest I see a turtle: Hands flat one on top of each other, palms down, waving thumbs up and down togetherInstructor signals: You (all) watch me. (usually before demonstrating a skill): Point at diver(s) with forefinger, point at own eyes with forefinger and middle finger, point at own chest with forefinger. You try that now, or do it again: Gesture with open hand palm up towards student after a demonstration of a skill.
Muscle action that moves the axial skeleton work over a joint with an origin and insertion of the muscle on respective side. The insertion is on the bone deemed to move towards the origin during muscle contraction. Muscles are often present that engage in several actions of the joint; able to perform for example both flexion and extension of the forearm as in the biceps and triceps respectively. This is not only to be able to revert actions of muscles, but also brings on stability of the actions though muscle coactivation.
Since the user always places their fingers in a straight position, the measurements of the finger will stay the same and provide consistent verification. Lastly, there are behavioral features that are traced, specifically the length of the stroke, the time it takes, the velocity of the stroke, the tool or the area for each touch point in relation to finger size, the touch area size, the pressure applied, and the angle of the stroke. For one stroke, there are 13 behavioral features, and this increases to 26, 39, and 52 for up to four strokes.
Because of this, wider hand spacing is associated with training the pectorals and narrower hand spacing is associated with training the triceps. Both close and wide hand spacing trains the deltoid area. In addition to the major phasic (dynamic) muscles, the bench press also uses tonic (stabilizing) muscles, including the scapular stabilizers (serratus anterior, middle, and inferior trapezius), humeral head stabilizers (rotator cuff muscles), and core (transverse abdominis, obliques, multifidus, erector spinae, quadratus lumborum.)
|
Testing what usually requires making observations or performing experiments?
|
[
"variables",
"hypothesis",
"conclusion",
"homeostasis"
] |
B
|
Usually, testing a hypothesis requires making observations or performing experiments. In this case, we will look into existing scientific literature to see if either of these hypotheses can be disproved, or if one or both can be supported by the data.
Suitable tests of a hypothesis compare the expected values from the tests of that hypothesis with the actual results of those tests. Scientists (and other people) can then secure, or discard, their hypotheses by conducting suitable experiments.
Experimental archaeology (also called experiment archaeology) is a field of study which attempts to generate and test archaeological hypotheses, usually by replicating or approximating the feasibility of ancient cultures performing various tasks or feats. It employs a number of methods, techniques, analyses, and approaches, based upon archaeological source material such as ancient structures or artifacts.It is distinct from uses of primitive technology without any concern for archaeological or historical study. Living history and historical reenactment, which are generally undertaken as hobbies, are non-archaeological counterparts of this academic discipline. One of the main forms of experimental archaeology is the creation of copies of historical structures using only historically accurate technologies.
Numerical software execution results or through-put on a network test, for example, provides analytical evidence that the requirement has been met. Inspection of vendor documentation or spec sheets also verifies requirements. Testing or demonstrating the software in a lab environment also verifies the requirements: a test type of verification will occur when test equipment not normally part of the lab (or system under test) is used.
Some analysers require samples to be transferred to sample cups. However, the need to protect the health and safety of laboratory staff has prompted many manufacturers to develop analysers that feature closed tube sampling, preventing workers from direct exposure to samples. Samples can be processed singly, in batches, or continuously. The automation of laboratory testing does not remove the need for human expertise (results must still be evaluated by medical technologists and other qualified clinical laboratory professionals), but it does ease concerns about error reduction, staffing concerns, and safety.
Lab tests may be required, including complete blood count (CBC), urine toxicology, drug levels from blood, cultures, coagulation tests, assays for thyroid function, or DNA typing. In some cases CT scan, magnetic resonance imaging, psychological testing, electroencephalography, or electrocardiography may also be employed.
|
This sharing of electrons produces what is known as a covalent bond. covalent bonds are ~20 to 50 times stronger than what?
|
[
"Mendelian systems",
"Newton's third law",
"gravitational pull",
"van der waals interactions"
] |
D
|
any other electron, they become a part of the molecule’s electron system.204 This sharing of electrons produces what is known as a covalent bond. Covalent bonds are ~20 to 50 times stronger than van der Waals interactions. What exactly does that mean? Basically, it takes 20 to 50 times more energy to break a covalent bond compared to a van der Waals interaction. While the bonded form of atoms in a molecule is always more stable than the unbounded form, it may not be stable enough to withstand the energy delivered through collisions with neighboring molecules. Different bonds between different atoms in different molecular contexts differ in terms of bond stability; the bond energy refers the energy needed to break a particular bond. A molecule is stable if the bond energies associated with bonded atoms within the molecule are high enough to survive the energy delivered to the molecule through either collisions with neighboring molecules or the absorption of energy (light). When atoms form a covalent bond, their individual van der Waals surfaces merge to produce a new molecular van der Waals surface. There are a number of ways to draw molecules, but the spacefilling or van der Waals surface view is the most realistic (at least for our purposes). While realistic it can also be confusing, since it obscures the underlying molecular structure, that is, how the atoms in the molecule are linked together. This can be seen in this set of representations of the simple molecule 2methylpropane (→).205 As molecules become larger, as is the case with many biologically important molecules, it can become impossible to appreciate their underlying organization based on a van der Waals surface representation. Because they form a new stable entity, it is not surprising (perhaps) that the properties of a molecule are quite distinct from, although certainly influenced by, the properties of the atoms from which they are composed. To a first order approximation, a molecule’s properties are based on its shape, which is dictated by how the various atoms withjn the molecule are connected to one another. These geometries are imposed by each atom’s underlying quantum mechanical properties and (particularly as molecules get larger, as they so often do in biological systems) the interactions between different parts of the molecule with one another. Some atoms, common to biological systems, such as hydrogen (H), can form only a single covalent bond. Others can make two (oxygen (O) and sulfur (S)), three (nitrogen (N)), four (carbon (C)), or five (phosphorus (P)) bonds. In addition to smaller molecules, biological systems contain a number of distinct types of extremely large molecules, composed of many thousands of atoms; these are known as macromolecules. Such macromolecules are not rigid; they can often fold back on themselves leading to intramolecular interactions. There are also interactions between molecules. The strength and specificity of these interactions can vary dramatically and even small changes in molecular structure (such as caused by mutations and allelic variations) can have dramatic effects.
The protonated forms of CO, HCN and N2 are said to have even stronger bonds, although another study argues that the use of BDE as a measure of bond strength in these cases is misleading.On the other end of the scale, there is no clear boundary between a very weak covalent bond and an intermolecular interaction. Lewis acid–base complexes between transition metal fragments and noble gases are among the weakest of bonds with substantial covalent character, with (CO)5W:Ar having a W–Ar bond dissociation energy of less than 3.0 kcal/mol. Held together entirely by the van der Waals force, helium dimer, He2, has the lowest measured bond dissociation energy of only 0.021 kcal/mol.
Atomic orbitals (except for s orbitals) have specific directional properties leading to different types of covalent bonds. Sigma (σ) bonds are the strongest covalent bonds and are due to head-on overlapping of orbitals on two different atoms. A single bond is usually a σ bond. Pi (π) bonds are weaker and are due to lateral overlap between p (or d) orbitals.
This transfer causes one atom to assume a net positive charge, and the other to assume a net negative charge. The bond then results from electrostatic attraction between the positive and negatively charged ions. Ionic bonds may be seen as extreme examples of polarization in covalent bonds.
Compounds with formal C≡O triple bonds do not exist except for carbon monoxide, which has a very short, strong bond (112.8 pm), and acylium ions, R–C≡O+ (typically 110-112 pm). Such triple bonds have a very high bond energy, even higher than N–N triple bonds. Oxygen can also be trivalent, for example in triethyloxonium tetrafluoroborate. : 343
Two electrons fill the lower-energy bonding orbital, σg(1s), while the remaining two fill the higher-energy antibonding orbital, σu*(1s). Thus, the resulting electron density around the molecule does not support the formation of a bond between the two atoms; without a stable bond holding the atoms together, the molecule would not be expected to exist. Another way of looking at it is that there are two bonding electrons and two antibonding electrons; therefore, the bond order is 0 and no bond exists (the molecule has one bound state supported by the Van der Waals potential).
|
Water molecules move about continuously due to what type of energy?
|
[
"seismic",
"potential",
"kinetic",
"optical"
] |
C
|
Water molecules move about continuously due to their kinetic energy. When a crystal of sodium chloride is placed into water, the water’s molecules collide with the crystal lattice. Recall that the crystal lattice is composed of alternating positive and negative ions. Water is attracted to the sodium chloride crystal because water is polar and has both a positive and a negative end. The positively charged sodium ions in the crystal attract the oxygen end of the water molecules because they are partially negative. The negatively charged chloride ions in the crystal attract the hydrogen end of the water molecules because they are partially positive. The action of the polar water molecules takes the crystal lattice apart (see image below).
Even though these motions are called "internal", the external portions of molecules still move—rather like the jiggling of a stationary water balloon. This permits the two-way exchange of kinetic energy between internal motions and translational motions with each molecular collision. Accordingly, as internal energy is removed from molecules, both their kinetic temperature (the kinetic energy of translational motion) and their internal temperature simultaneously diminish in equal proportions.
These components are experimentally determined by calorimetry. The hydrophobic effect was found to be entropy-driven at room temperature because of the reduced mobility of water molecules in the solvation shell of the non-polar solute; however, the enthalpic component of transfer energy was found to be favorable, meaning it strengthened water-water hydrogen bonds in the solvation shell due to the reduced mobility of water molecules.
Since water has a tendency to move toward lower energy levels, water will want to travel toward the zone of higher solute concentrations. Although, liquid water will only move in response to such differences in osmotic potential if a semipermeable membrane exists between the zones of high and low osmotic potential. A semipermeable membrane is necessary because it allows water through its membrane while preventing solutes from moving through its membrane.
The electronic transitions of molecules in solution can depend strongly on the type of solvent with additional bathochromic shifts or hypsochromic shifts.
Fluid, usually water, in the absorber tubes collect the trapped heat and transfer it to a heat storage vault. Heat is transferred either by conduction or convection. When water is heated, kinetic energy is transferred by conduction to water molecules throughout the medium.
|
A small scale version of what type of map displays individual rock units?
|
[
"seismic map",
"geographic map",
"geologic map",
"polar map"
] |
C
|
Geologic maps display rock units and geologic features. A small scale map displays individual rock units while a large scale map shows geologic provinces.
One of the most important applications of the topographic profiles is in the construction of works of great length and small width, for example roads, sewers or pipelines.Sometimes topographical profiles appear in printed maps, such as those designed for navigation routes, excavations and especially for geological maps, where they are used to show the internal structure of the rocks that populate a territory. People who study natural resources such as geologists, geomorphologists, soil scientists and vegetation scholars, among others, build profiles to observe the relationship of natural resources to changes in topography and analyze numerous problems.
map A picture of a place drawn at an established scale on a two-dimensional plane surface, often depicting natural and manmade features on or under the surface of the Earth or other planetary body, typically with the features positioned as accurately as possible relative to a coordinate reference system; more generally, any graphical representation of locative information about the relative positions of particular features within a space or place. map index Also index map. A graphical key identifying the relationships between the individual maps of a map series, their coverage areas, and/or their production status or availability.
In the study of rock and sediment strata, geologists have recognized a number of different types of strata, including bed, flow, band, and key bed. A bed is a single stratum that is lithologically distinguishable from other layers above and below it. In the classification hierarchy of sedimentary lithostratigraphic units, a bed is the smallest formal unit. However, only beds that are distinctive enough to be useful for stratigraphic correlation and geologic mapping are customarily given formal names and considered formal lithostratigraphic units.
Traditional maps are abstractions of the real world, a sampling of important elements portrayed on a sheet of paper with symbols to represent physical objects. People who use maps must interpret these symbols. Topographic maps show the shape of land surface with contour lines or with shaded relief.
Then these measured values are corrected for various corrections and an anomaly map is prepared. By analyzing these anomaly maps one can get an idea about the structure of rock formations in that area. For this purpose one need to use various analog or digital filters.
|
What is defined as a change in the inherited traits of organisms over time?
|
[
"variation",
"evolution",
"divergence",
"generation"
] |
B
|
One idea is that evolution happens. Evolution is a change in the inherited traits of organisms over time. Living things have changed as descendants diverged from common ancestors in the past.
When analyzing the types of changes that can occur to a phenotype, we can see changes that are behavioral, morphological, or physiological. A characteristic of the phenotype that arises through adaptive maternal effects, is the plasticity of this phenotype. Phenotypic plasticity allows organisms to adjust their phenotype to various environments, thereby enhancing their fitness to changing environmental conditions. Ultimately it is a key attribute to an organism's, and a population's, ability to adapt to short term environmental change.Phenotypic plasticity can be seen in many organisms, one species that exemplifies this concept is the seed beetle Stator limbatus.
However, if the change has a positive influence, the mutation may become more and more common in a population until it becomes a fixed genetic piece of that population. Organisms changing via these two options comprise the classic view of natural selection.
Epigenetic inheritance may only affect fitness if it predictably alters a trait under selection. Evidence has been forwarded that environmental stimuli are important agents in the alteration of epigenes. Ironically, Darwinian evolution may act on these neo-Lamarckian acquired characteristics as well as the cellular mechanisms producing them (e.g. methyltransferase genes). Epigenetic inheritance may confer a fitness benefit to organisms that deal with environmental changes at intermediate timescales.
As Bateman and Dimichele say " the alternation of generations has become a terminological morass; often, one term represents several concepts or one concept is represented by several terms. "Possible variations are: Relative importance of the sporophyte and the gametophyte.
In contrast, if an organism's current behavior is altered by past experiences, then the animal is said to be exhibiting developmental or "innate" behavioral plasticity. This form of plasticity is generally thought to require new neuronal pathways to form. Developmental behavioral plasticity corresponds to the commonly used definition of plasticity: a single genotype can express more than one behavioral phenotype as a result of different developmental routes triggered by differences in past experiences.
|
What hormone, which is associated with luteinizing hormone and male sexuality, helps bring about physical changes in puberty?
|
[
"steroids",
"epinephrine",
"testosterone",
"estrogen"
] |
C
|
What causes puberty to begin? The hypothalamus in the brain “tells” the pituitary gland to secrete hormones that target the testes. The main pituitary hormone involved is luteinizing hormone (LH) . It stimulates the testes to secrete testosterone. Testosterone, in turn, promotes protein synthesis and growth. It brings about most of the physical changes of puberty, some of which are shown in Figure below . In addition to the changes shown below, during puberty male facial hair begins to grow, the shoulders broaden, and the male voice deepens. You can watch an animation of these and other changes that occur in boys during puberty at the Interactive Body link: http://www. bbc. co. uk/science/humanbody/body/interactives/lifecycle/teenagers/ .
The increased secretion of testosterone from the testes during puberty causes the male secondary sexual characteristics to be manifested. Testosterone directly increases size and mass of muscles, vocal cords, and bones, deepening of the voice, and changing the shape of the face and skeleton. Converted into DHT in the skin, it accelerates growth of androgen-responsive facial and body hair but may slow and eventually stop the growth of head hair. Taller stature is largely a result of later puberty and slower epiphyseal fusion.
Adrenocorticotropic hormone release is triggered by corticotropin-releasing hormone and inhibited by rising glucocorticoid levels. The gonadotropins—follicle-stimulating hormone and luteinizing hormone regulate the functions of the gonads in both sexes. Follicle-stimulating hormone stimulates sex cell production; luteinizing hormone stimulates gonadal hormone production.
Enclomiphene is a selective estrogen receptor antagonist, antagonizing the estrogen receptors in the pituitary gland, disrupting the negative feedback loop by estrogen towards the hypothalamic-pituitary-gonadal axis, ultimately resulting in an increase in gonadotropin secretion. In men with secondary hypogonadotropic hypogonadism, this improves testosterone levels and sperm motility. Men with secondary hypogonadotropic hypogonadism have abnormally low testosterone levels due to low-normal levels of luteinizing hormone (LH) and follicular stimulating hormone (FSH). The biological role of these hormones is to stimulate the endogenous production of testosterone by the testes.
Apocrine sweat contains relatively high amounts of androgens, for instance dehydroepiandrosterone (DHEA), androsterone, and testosterone, and the androgen receptor (AR), the biological target of androgens, is strongly expressed in the secretory cells of apocrine glands. In addition, 5α-reductase type I, an enzyme which converts testosterone into the more potent androgen dihydrotestosterone (DHT), has been found to be highly expressed in the apocrine glands of adolescents, and DHT has been found to specifically contribute to malodor as well. Starting at puberty, males have higher levels of androgens than do females and produce comparatively more axillary malodor. As such, it has been proposed that the higher axillary malodor seen in males is due to greater relative stimulation of axillary apocrine sweat glands by androgens.
: 833 When an oocyte completes its maturation in the ovary, a surge of luteinizing hormone is secreted by the pituitary gland which stimulates the release of the oocyte through the rupture of the follicle, a process called ovulation. The follicle remains functional and reorganizes into a corpus luteum, which secretes progesterone in order to prepare the uterus for an eventual implantation of the embryo. : 839
|
Where do angiosperms produce seeds in flowers?
|
[
"ovaries",
"germs",
"cones",
"testes"
] |
A
|
Seed plants called angiosperms produce seeds in the ovaries of flowers.
Angiosperms were formerly called Magnoliophyta ().Angiosperms are distinguished from the other seed-producing plants, the gymnosperms, by having flowers, xylem consisting of vessel elements instead of tracheids, endosperm within their seeds, and fruits that completely envelop the seeds. The ancestors of flowering plants diverged from the common ancestor of all living gymnosperms before the end of the Carboniferous, over 300 million years ago. In the Cretaceous, angiosperms diversified explosively, becoming the dominant group of plants across the planet.
Following the evolution of the seed habit, seed plants diversified, giving rise to a number of now-extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. Gymnosperms produce "naked seeds" not fully enclosed in an ovary; modern representatives include conifers, cycads, Ginkgo, and Gnetales. Angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. Ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms.
The APG IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG). It was published in 2016, seven years after its predecessor the APG III system was published in 2009, and 18 years after the first APG system was published in 1998. In 2009, a linear arrangement of the system was published separately; the APG IV paper includes such an arrangement, cross-referenced to the 2009 one.Compared to the APG III system, the APG IV system recognizes five new orders (Boraginales, Dilleniales, Icacinales, Metteniusales and Vahliales), along with some new families, making a total of 64 angiosperm orders and 416 families. In general, the authors describe their philosophy as "conservative", based on making changes from APG III only where "a well-supported need" has been demonstrated. This has sometimes resulted in placements that are not compatible with published studies, but where further research is needed before the classification can be changed.
Although it is not the usual route of a microspore, this process is the most effective way of yielding haploid and double haploid plants through the use of male sex hormones. Under certain stressors such as heat or starvation, plants select for microspore embryogenesis. It was found that over 250 different species of angiosperms responded this way.
The flowers are produced in corymbs of one to four (occasionally up to seven) together in mid spring, each flower 3 millimetres (0.12 in) diameter, with five white to pale pink petals. The fruit is a dark red pome 6–8 millimetres (0.24–0.31 in) diameter, containing two or three seeds. It occurs on limestone soils, at altitudes of up to 2,800 metres (9,200 ft) altitude.
|
In order to create food, what do photosynthetic protists use?
|
[
"thermal energy",
"hydrocarbons",
"decayed matter",
"light energy"
] |
D
|
Photosynthetic protists use light energy to make food. They are major producers in aquatic ecosystems.
Most photosynthetic microbes are autotrophic, fixing carbon dioxide via the Calvin cycle. Some photosynthetic bacteria (e.g. Chloroflexus) are photoheterotrophs, meaning that they use organic carbon compounds as a carbon source for growth. Some photosynthetic organisms also fix nitrogen (see below).
It is the photosynthetic activity of the micro-algae in hospite that provides the essential nutrients for the worm. This partnership is called photosymbiosis, from "photo", "light", and symbiosis "who lives with". These photosynthetic marine animals live in colonies (up to several million individuals) on the tidal zone.
In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in cell membranes. In its simplest form, this involves the membrane surrounding the cell itself. However, the membrane may be tightly folded into cylindrical sheets called thylakoids, or bunched up into round vesicles called intracytoplasmic membranes.
This margin is also known as the littoral zone and contains much of the photosynthetic algae and plants of this ecosystem called macrophytes. Other photosynthetic organisms such as phytoplankton (suspended algae) and periphytons (organisms including cyanobacteria, detritus, and other microbes) thrive here and stand as the primary producers of pond food webs. Some grazing animals like geese and muskrats consume the wetland plants directly as a source of food.
During photosynthesis, primary producers take energy from the sun and convert it into energy, sugar, and oxygen. Primary producers also need the energy to convert this same energy elsewhere, so they get it from nutrients. One type of nutrient is nitrogen.
|
What type of vertebrates are birds?
|
[
"epidermal tetrapod",
"invertebrates",
"endothermic tetrapod",
"exothermic"
] |
C
|
Birds are endothermic tetrapod vertebrates. They are bipedal, which means they walk on two legs. Birds also lay amniotic eggs, and the eggs have hard, calcium carbonate shells. Although birds are the most recent class of vertebrates to evolve, they are now the most numerous vertebrates on Earth. Why have birds been so successful? What traits allowed them to increase and diversify so rapidly?.
Among living bird species, only the great albatrosses and the two largest species of pelican exceed the Andean condor in average and maximal wingspan. The adult plumage is all black, except for a frill of white feathers at the base of the neck and, especially in the male, large white bands on the wings, which only appear after the bird's first moult. The head and neck, kept meticulously clean, are red to blackish-red, and have few feathers.
The wings are green and the beak is black. The elongated tail feathers are absent in juveniles. Sexes are alike.The calls is a nasal trill tree-tree-tree-tree, usually given in flight.Leucistic individuals have been noted.
The female bill and feet are yellowish-brown to grey and their three outermost rectrices are also narrowly tipped with white. In immature birds, both male and female chicks have remiges, scapulars and wing coverts intermixed with buff, outer rectrices infused with white and feathers more narrow and pointed than adults. Immature females have a brown breast. Trogons are the only birds with a heterodactyl toe arrangement.
The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae. The last few are fused with the pelvis to form the synsacrum. The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings. The wings are more or less developed depending on the species; the only known groups that lost their wings are the extinct moa and elephant birds.
Paleontologist Lawrence Witmer concluded in 2009 that this evidence is sufficient to demonstrate that avian evolution went through a four-winged stage. Fossil evidence also demonstrates that birds and dinosaurs shared features such as hollow, pneumatized bones, gastroliths in the digestive system, nest-building and brooding behaviors. Although the origin of birds has historically been a contentious topic within evolutionary biology, only a few scientists still dispute the dinosaurian origin of birds, suggesting descent from other types of archosaurian reptiles. Within the consensus that supports dinosaurian ancestry, the exact sequence of evolutionary events that gave rise to the early birds within maniraptoran theropods is disputed. The origin of bird flight is a separate but related question for which there are also several proposed answers.
|
What type of ions do ionic compounds contain?
|
[
"regular and irregular",
"positive and charged",
"negative and neutal",
"positive and negative"
] |
D
|
An ionic compound contains positive and negative ions.
An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as 100 °C (212 °F). While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ionic liquids are largely made of ions. These substances are variously called liquid electrolytes, ionic melts, ionic fluids, fused salts, liquid salts, or ionic glasses.Ionic liquids have many potential applications.
Ionic bonding is a kind of chemical bonding that arises from the mutual attraction of oppositely charged ions. Ions of like charge repel each other, and ions of opposite charge attract each other. Therefore, ions do not usually exist on their own, but will bind with ions of opposite charge to form a crystal lattice. The resulting compound is called an ionic compound, and is said to be held together by ionic bonding.
In the case of a non-ionic compound the chemical bonds are non-ionic such meaning the compound will probably not dissolve in water or another polar solvent. Many non-ionic compounds have chemical bonds that share the electron density that binds them together. This type of chemical bond is either a non-polar covalent bond or a polar covalent bond.
This process is called solvation. The presence of these free ions makes aqueous ionic compound solutions good conductors of electricity. The same occurs when the compounds are heated above their melting point, i.e., they are melted. This process is known as ionization.
Some ionic compounds (salts) dissolve in water, which arises because of the attraction between positive and negative charges (see: solvation). For example, the salt's positive ions (e.g. Ag+) attract the partially negative oxygen atom in H2O. Likewise, the salt's negative ions (e.g. Cl−) attract the partially positive hydrogens in H2O. Note: the oxygen atom is partially negative because it is more electronegative than hydrogen, and vice versa (see: chemical polarity).
|
All living things need air and this to survive?
|
[
"stimuli",
"water",
"habitat",
"ecosystem"
] |
B
|
Oxygen is essential to all life. Plants and phytoplankton photosynthesize water and carbon dioxide and water, both oxides, in the presence of sunlight to form sugars with the release of oxygen. The sugars are then turned into such substances as cellulose and (with nitrogen and often sulfur) proteins and other essential substances of life.
Similarly, in order for human beings to live, it is necessary that they have air.One can also say S is a sufficient condition for N (refer again to the third column of the truth table immediately below). If the conditional statement is true, then if S is true, N must be true; whereas if the conditional statement is true and N is true, then S may be true or be false.
The presence of oxygen and water vapour in the atmosphere could be evidence for life. Oxygen is very reactive so if large amounts of oxygen exist in a planet's atmosphere some process such as photosynthesis must be continuously producing it. The presence of oxygen alone, however, is not conclusive evidence for life.
The body's circulatory system transports the oxygen to the cells, where cellular respiration takes place.Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Carl Sagan and others in the 1960s and 1970s computed conditions for hypothetical microorganisms living in the atmosphere of Jupiter. The intense radiation and other conditions, however, do not appear to permit encapsulation and molecular biochemistry, so life there is thought unlikely. In addition, as a gas giant Jupiter has no surface, so any potential microorganisms would have to be airborne.
|
The cells of all eukarya have a what?
|
[
"chloroplast",
"nucleus",
"epidermis",
"necrosis"
] |
B
|
Some Eukarya are also single-celled, but many are multicellular. Some have a cell wall; others do not. However, the cells of all Eukarya have a nucleus and other organelles.
Eukaryotes have a nucleus where DNA is contained. They are usually larger than prokaryotes and contain many more organelles. The nucleus, the feature of a eukaryote that distinguishes it from a prokaryote, contains a nuclear envelope, nucleolus and chromatin. In cytoplasm, endoplasmic reticulum (ER) synthesizes membranes and performs other metabolic activities.
Some eukaryotic cells (plant cells and fungal cells) also have a cell wall. Inside the cell is the cytoplasmic region that contains the genome (DNA), ribosomes and various sorts of inclusions. The genetic material is freely found in the cytoplasm.
There are two types of cells: prokaryotes and eukaryotes. Prokaryotes were the first of the two to develop and do not have a self-contained nucleus. Their mechanisms are simpler than later-evolved eukaryotes, which contain a nucleus that envelops the cell's DNA and some organelles.
It contains numerous granulosa cells.
Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. This involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya. Later on, some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms.
|
What type of plate boundaries produce huge mountain ranges in the ocean basin?
|
[
"divergent",
"coherent",
"parallel",
"tractional"
] |
A
|
Divergent plate boundaries produce huge mountain ranges under water in every ocean basin.
There are three main types of mountains: volcanic, fold, and block. All three types are formed from plate tectonics: when portions of the Earth's crust move, crumple, and dive. Compressional forces, isostatic uplift and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features. The height of the feature makes it either a hill or, if higher and steeper, a mountain. Major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity.
Current plate boundaries are defined by their seismicity. Past plate boundaries within existing plates are identified from a variety of evidence, such as the presence of ophiolites that are indicative of vanished oceans.
Vertical displacement resulting from tectonic activity occurs at divergent and convergent plate boundaries. The movement of magma in the asthenosphere can create divergent plate boundaries as the magma begins to rise and protrude weaker lithospheric crust. Subsidence at a divergent plate boundary is a form of vertical displacement which occurs when a plate begins to split apart. As intrusive magma widens the rift zone of a divergent plate boundary the layers of crust on the surface above the rift will subside into the rift, creating a vertical displacement of those layers of surface crust.Convergent plate boundaries create orogenies such as the Laramide orogeny that raised the Rocky Mountains.
plate tectonics A geologic theory that the bending (folding) and breaking (faulting) of the solid surface of the Earth results from the slow movement of large sections of that surface called plates. plateau Also high plain or tableland. A large area of relatively flat terrain that is significantly higher in elevation than the surrounding landscape, often with one or more sides with steep slopes.
This produced mild, uniform climates that persisted throughout most of geologic time. But during the Cenozoic Era, the large North American and South American continental plates drifted westward from the Eurasian plate. This interlocked with the development of the Atlantic Ocean, running north–south, with the North Pole in the small, nearly landlocked basin of the Arctic Ocean.
|
Interstitial carbides are produced by the reaction of most transition metals at high temperatures with what element?
|
[
"hydrogen",
"oxygen",
"carbon",
"nitrogen"
] |
C
|
temperatures with electropositive metals such as those of groups 1 and 2 and aluminum produces ionic carbides, which contain discrete metal cations and carbon anions. The identity of the anions depends on the size of the second element. For example, smaller elements such as beryllium and aluminum give methides such as Be2C and Al4C3, which formally contain the C4− ion derived from methane (CH4) by losing all four H atoms as protons. In contrast, larger metals such as sodium and calcium give carbides with stoichiometries of Na2C2 and CaC2. Because these carbides contain the C4− ion, which is derived from acetylene (HC≡CH) by losing both H atoms as protons, they are more properly called acetylides. As discussed in Chapter 21 "Periodic Trends and the ", Section 21.4 "The Alkaline Earth Metals (Group 2)", reacting ionic carbides with dilute aqueous acid results in protonation of the anions to give the parent hydrocarbons: CH4 or C2H2. For many years, miners’ lamps used the reaction of calcium carbide with water to produce a steady supply of acetylene, which was ignited to provide a portable lantern. The reaction of carbon with most transition metals at high temperatures produces interstitial carbides. Due to the less electropositive nature of the transition metals, these carbides contain covalent metal– carbon interactions, which result in different properties: most interstitial carbides are good conductors of electricity, have high melting points, and are among the hardest substances known. Interstitial carbides exhibit a variety of nominal compositions, and they are often nonstoichiometric compounds whose carbon content can vary over a wide range. Among the most important are tungsten carbide (WC), which is used industrially in high-speed cutting tools, and cementite (Fe3C), which is a major component of steel. Elements with an electronegativity similar to that of carbon form covalent carbides, such as silicon carbide (SiC; Equation 22.15) and boron carbide (B4C). These substances are extremely hard, have high melting points, and are chemically inert. For example, silicon carbide is highly resistant to chemical attack at temperatures as high as 1600°C. Because it also maintains its strength at high temperatures, silicon carbide is used in heating elements for electric furnaces and in variable-temperature resistors.
They are all III-V semiconductors isoelectronic to silicon and germanium, all of which but AlN have the zinc blende structure. All four can be made by high-temperature (and possibly high-pressure) direct reaction of their component elements.Aluminium alloys well with most other metals (with the exception of most alkali metals and group 13 metals) and over 150 intermetallics with other metals are known. Preparation involves heating fixed metals together in certain proportion, followed by gradual cooling and annealing.
In practice and industry, this reduction of Gibbs free energy is termed stress relief.The relief of internal stresses is a thermodynamically spontaneous process; however, at room temperatures, it is a very slow process. The high temperatures at which annealing occurs serve to accelerate this process.The reaction that facilitates returning the cold-worked metal to its stress-free state has many reaction pathways, mostly involving the elimination of lattice vacancy gradients within the body of the metal. The creation of lattice vacancies is governed by the Arrhenius equation, and the migration/diffusion of lattice vacancies are governed by Fick's laws of diffusion.In steel, there is a decarburization mechanism that can be described as three distinct events: the reaction at the steel surface, the interstitial diffusion of carbon atoms and the dissolution of carbides within the steel.
Above approximately 900 °C a typical low-carbon steel is composed entirely of austenite, a high-temperature phase of iron that has a cubic close-packed crystal structure. On cooling, it tends to transform into a mixture of phases, ferrite and cementite, depending on the exact chemical composition. A steel of eutectoid composition will under equilibrium conditions transform into pearlite – an interleaved mixture of ferrite and cementite (Fe3C).
Barium carbide can be synthesized as an impure compound by reducing barium carbonate powder with metallic magnesium in the presence of carbon-14. Carbon-14 containing barium carbide can also be made by reducing 14C carbon dioxide with hot barium metal at 600°C. These methods are used because of their high yield, and because the carbide is used to make acetylene.
The most prevalent hydrides of the transition metals are metal complexes that contain a mix of ligands in addition to hydride. The range of coligands is large. Virtually all of the metals form such derivatives.
|
Fungus-like protist saprobes play what role in a food chain and are specialized to absorb nutrients from nonliving organic matter, such as dead organisms or their wastes?
|
[
"aphids",
"Soil",
"fluxes",
"decomposers"
] |
D
|
Agents of Decomposition The fungus-like protist saprobes are specialized to absorb nutrients from nonliving organic matter, such as dead organisms or their wastes. For instance, many types of oomycetes grow on dead animals or algae. Saprobic protists have the essential function of returning inorganic nutrients to the soil and water. This process allows for new plant growth, which in turn generates sustenance for other organisms along the food chain. Indeed, without saprobe species, such as protists, fungi, and bacteria, life would cease to exist as all organic carbon became “tied up” in dead organisms.
Microorganisms are diverse and include all bacteria and archaea, most protists including algae, protozoa and fungal-like protists, as well as certain microscopic animals such as rotifers. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses as microorganisms, but others consider these as non-living.Microorganisms are crucial to nutrient recycling in ecosystems as they act as decomposers.
Through this process of eating the detritus many times over and harvesting the microorganisms from it, the detritus thins out, becomes fractured and becomes easier for the microorganisms to use, and so the complex carbohydrates are also steadily broken down and disappear over time. What is left behind by the detritivores is then further broken down and recycled by decomposers, such as bacteria and fungi. This detritus cycle plays a large part in the so-called purification process, whereby organic materials carried in by rivers is broken down and disappears, and an extremely important part in the breeding and growth of marine resources. In ecosystems on land, far more essential material is broken down as dead material passing through the detritus chain than is broken down by being eaten by animals in a living state. In both land and aquatic ecosystems, the role played by detritus is too large to ignore.
In food webs, saprophages generally play the roles of decomposers. There are two main branches of saprophages, broken down by nutrient source. There are necrophages which consume dead animal biomass, and thanatophages which consume dead plant biomass.
In 2008, Euprenolepis procera a species of ant from the rainforests of South East Asia was found to harvest mushrooms from the rainforest. Witte & Maschwitz found that their diet consisted almost entirely of mushrooms, representing a previously undiscovered feeding strategy in ants. Several beetle families, including the Erotylidae, Endomychidae, and certain Tenebrionidae also are specialists on fungi, though they may eat other foods occasionally. Other insects, like fungus gnats and scuttle flies, utilize fungi at their larval stage. Feeding on fungi is crucial for dead wood eaters as this is the only way to acquire nutrients not available in nutritionally scarce dead wood.
Another interesting example of a bacteria living in symbiosis with a fungus is with the fungus Mortierella. This soil-dwelling fungus lives in close association with a toxin-producing bacteria, Mycoavidus, which helps the fungus to defend against nematodes. This is a very new, but potentially very important, area of study within the study of symbiosis.
|
What are the sites of protein synthesis or assembly?
|
[
"chloroplasts",
"ribosomes",
"chromosomes",
"plasma"
] |
B
|
Ribosomes are small organelles and are the sites of protein synthesis (or assembly). They are made of ribosomal protein and ribosomal RNA, and are found in both eukaryotic and prokaryotic cells. Unlike other organelles, ribosomes are not surrounded by a membrane. Each ribosome has two parts, a large and a small subunit, as shown in Figure below . The subunits are attached to one another. Ribosomes can be found alone or in groups within the cytoplasm. Some ribosomes are attached to the endoplasmic reticulum (ER) (as shown in Figure below ), and others are attached to the nuclear envelope.
Techniques are used to affect the amino acid sequence of the protein (site-directed mutagenesis), the folding and conformation of the protein, or the folding of a single tertiary protein within a quaternary protein matrix. Proteins that are the main focus of manipulation are typically enzymes. These are proteins that act as catalysts for biochemical reactions. By manipulating these catalysts, the reaction rates, products, and effects can be controlled. Enzymes and proteins are important to the biological field and research that there are specific divisions of engineering focusing only on proteins and enzymes.
SAAB experimental procedure consists of several steps, depending upon the knowledge available about the binding site. A typical SAAB consists of the following steps: Synthesis of template with random sequence in binding site: three situations are possible: (i) when both the binding site and the protein are known and available; (ii) when only a consensus binding site is available and the binding protein is not; and (iii) when the protein is available, but the binding site is unknown. When the binding site is not known, the number of random nucleotide positions in the template must be large. Incubate labeled double stranded template with protein: usually the protein has to be synthesized in a host cell with fusion techniques.
Many amino acids, such as ornithine, are metabolic intermediates produced biosynthetically, but not incorporated translationally into proteins. Post-translational modification of amino acid residues in proteins leads to the formation of many proteinaceous, but non-proteinogenic, amino acids. Other amino acids are solely found in abiotic mixes (e.g. α-methylnorvaline). Over 30 unnatural amino acids have been inserted translationally into protein in engineered systems, yet are not biosynthetic.
Cell-free protein synthesis, also known as in vitro protein synthesis or CFPS, is the production of protein using biological machinery in a cell-free system, that is, without the use of living cells. The in vitro protein synthesis environment is not constrained by a cell wall or homeostasis conditions necessary to maintain cell viability. Thus, CFPS enables direct access and control of the translation environment which is advantageous for a number of applications including co-translational solubilisation of membrane proteins, optimisation of protein production, incorporation of non-natural amino acids, selective and site-specific labelling. Due to the open nature of the system, different expression conditions such as pH, redox potentials, temperatures, and chaperones can be screened. Since there is no need to maintain cell viability, toxic proteins can be produced.
Structure-based combinatorial protein engineering (SCOPE) is a synthetic biology technique for creating gene libraries (lineages) of defined composition designed from structural and probabilistic constraints of the encoded proteins. The development of this technique was driven by fundamental questions about protein structure, function, and evolution, although the technique is generally applicable for the creation of engineered proteins with commercially desirable properties. Combinatorial travel through sequence spacetime is the goal of SCOPE.
|
What must replicate in the cell cycle before meiosis i takes place?
|
[
"cell walls",
"dna",
"sperm",
"meiotic fluid"
] |
B
|
Meiosis I begins after DNA replicates during interphase of the cell cycle. In both meiosis I and meiosis II , cells go through the same four phases as mitosis - prophase, metaphase, anaphase and telophase. However, there are important differences between meiosis I and mitosis. The eight stages of meiosis are summarized below. The stages will be described for a human cell, starting with 46 chromosomes.
Synthesis (S) phase: The genetic material is replicated; each of the cell's chromosomes duplicates to become two identical sister chromatids attached at a centromere. This replication does not change the ploidy of the cell since the centromere number remains the same.
M phase See mitosis. meiosis A specialized type of cell division which occurs exclusively in sexually reproducing eukaryotes, during which DNA replication is followed by two consecutive rounds of cell division to ultimately produce four genetically unique daughter cells, each with half the number of chromosomes as the original parent cell. Meiosis only occurs in cells of the sex organs, and serves the purpose of generating haploid gametes such as sperm, eggs, or spores, which are later fused during fertilization. The two meiotic divisions, known as Meiosis I and Meiosis II, may also include various genetic recombination events between homologous chromosomes.
Meiosis only occurs in cells of the sex organs, and serves the purpose of generating haploid gametes such as sperm, eggs, or spores, which are later fused during fertilization. The two meiotic divisions, known as Meiosis I and Meiosis II, may also include various genetic recombination events between homologous chromosomes. meiotic spindle See spindle apparatus.
Cytokinesis, the pinching of the cell membrane in animal cells or the formation of the cell wall in plant cells, occurs, completing the creation of two daughter cells. However, cytokinesis does not fully complete resulting in "cytoplasmic bridges" which enable the cytoplasm to be shared between daughter cells until the end of meiosis II. Sister chromatids remain attached during telophase I. Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.
The next stage of prophase I in meiosis is the zygotene stage. : 27: 353 During this stage, the chromosomes attach themselves by their ends (telomeres) to the inner membrane of the nuclear envelope. At the transition to the zygotene stage the telomeres usually aggregate at a nuclear envelope sector, thereby forming a meiotic bouquet.
|
What phenomenon is primarily the result of plate tectonic motions?
|
[
"earthquake",
"eruption",
"tsunamis",
"volcanoes"
] |
A
|
Earthquakes are primarily the result of plate tectonic motions. What type of stress would cause earthquakes at each of the three types of plate boundaries?.
plate tectonics A geologic theory that the bending (folding) and breaking (faulting) of the solid surface of the Earth results from the slow movement of large sections of that surface called plates. plateau Also high plain or tableland. A large area of relatively flat terrain that is significantly higher in elevation than the surrounding landscape, often with one or more sides with steep slopes.
Vertical displacement resulting from tectonic activity occurs at divergent and convergent plate boundaries. The movement of magma in the asthenosphere can create divergent plate boundaries as the magma begins to rise and protrude weaker lithospheric crust. Subsidence at a divergent plate boundary is a form of vertical displacement which occurs when a plate begins to split apart. As intrusive magma widens the rift zone of a divergent plate boundary the layers of crust on the surface above the rift will subside into the rift, creating a vertical displacement of those layers of surface crust.Convergent plate boundaries create orogenies such as the Laramide orogeny that raised the Rocky Mountains.
As the overlying tectonic plate moves over this hotspot, the eruption of magma from the fixed plume onto the surface is expected to form a chain of volcanoes that parallels plate motion. The Hawaiian Islands chain in the Pacific Ocean is the archetypal example. It has recently been discovered that the volcanic locus of this chain has not been fixed over time, and it thus joined the club of the many type examples that do not exhibit the key characteristic originally proposed.The eruption of continental flood basalts is often associated with continental rifting and breakup. This has led to the hypothesis that mantle plumes contribute to continental rifting and the formation of ocean basins.
Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with the article "Seismology and the New Global Tectonics", published in 1968, using data collected from seismologic stations, including those he set up in the South Pacific. The modern theory of plate tectonics, refining Wegener, explains that there are two kinds of crust of different composition: continental crust and oceanic crust, both floating above a much deeper "plastic" mantle. Continental crust is inherently lighter. Oceanic crust is created at spreading centers, and this, along with subduction, drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance.
The movement of the island arcs towards the continent could be possible if, at some point, the ancient Benioff zones dipped toward the present ocean rather than toward the continent, as in most arcs today. This will have resulted in the loss of ocean floor between the arc and the continent, and consequently, in the migration of the arc during spreading episodes.The fracture zones in which some active island arcs terminate may be interpreted in terms of plate tectonics as resulting from movement along transform faults, which are plate margins where the crust is neither being consumed nor generated. Thus the present location of these inactive island chains is due to the present pattern of lithospheric plates. However, their volcanic history, which indicates that they are fragments of older island arcs, is not necessarily related to the present plate pattern and may be due to differences in position of plate margins in the past.
|
What is a group of neuron cell bodies in the periphery called?
|
[
"ganglion",
"crystals",
"organism",
"gangism"
] |
A
|
Ganglia A ganglion is a group of neuron cell bodies in the periphery. Ganglia can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. The most common type of sensory ganglion is a dorsal (posterior) root ganglion. These ganglia are the cell bodies of neurons with axons that are sensory endings in the periphery, such as in the skin, and that extend into the CNS through the dorsal nerve root. The ganglion is an enlargement of the nerve root. Under microscopic inspection, it can be seen to include the cell bodies of the neurons, as well as bundles of fibers that are the posterior nerve root (Figure 13.19). The cells of the dorsal root ganglion are unipolar cells, classifying them by shape. Also, the small round nuclei of satellite cells can be seen surrounding—as if they were orbiting—the neuron cell bodies.
Brain cells make up the functional tissue of the brain. The rest of the brain tissue is structural or connective called the stroma which includes blood vessels. The two main types of cells in the brain are neurons, also known as nerve cells, and glial cells also known as neuroglia.Neurons are the excitable cells of the brain that function by communicating with other neurons and interneurons (via synapses), in neural circuits and larger brain networks.
The mossy fiber and climbing fiber inputs each carry fiber-specific information; the cerebellum also receives dopaminergic, serotonergic, noradrenergic, and cholinergic inputs that presumably perform global modulation.The cerebellar cortex is divided into three layers. At the bottom lies the thick granular layer, densely packed with granule cells, along with interneurons, mainly Golgi cells but also including Lugaro cells and unipolar brush cells. In the middle lies the Purkinje layer, a narrow zone that contains the cell bodies of Purkinje cells and Bergmann glial cells.
However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column. To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell.
The autonomic nervous system itself consists of two parts: the sympathetic nervous system and the parasympathetic nervous system. Some authors also include sensory neurons whose cell bodies lie in the periphery (for senses such as hearing) as part of the PNS; others, however, omit them.The vertebrate nervous system can also be divided into areas called gray matter and white matter.
This region is known as the paleomammalian brain, the major parts of which are the hippocampi and amygdalas, often referred to as the limbic system. The limbic system deals with more complex functions including emotional, sexual and fighting behaviors. Of course, animals that are not vertebrates also have brains, and their brains have undergone separate evolutionary histories.The brainstem and limbic system are largely based on nuclei, which are essentially balled-up clusters of tightly packed neurons and the axon fibers that connect them to each other, as well as to neurons in other locations.
|
Where does most of our food come from?
|
[
"angiosperms",
"microbes",
"lichen",
"gymnosperms"
] |
A
|
Approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies has been, and continues to be, a major source of food for many parts of the world, providing 6.5% of global protein. Much of the long-distance trade of commodities (such as oil, natural gas, and manufactured products) is transported by boats through seas, rivers, lakes, and canals.
Traditional sources of animal feed include household food scraps and the byproducts of food processing industries such as milling and brewing. Material remaining from milling oil crops like peanuts, soy, and corn are important sources of fodder. Scraps fed to pigs are called slop, and those fed to chicken are called chicken scratch.
Traditional sources of animal feed include household food scraps and the byproducts of food processing industries such as milling and brewing. Material remaining from milling oil crops like peanuts, soy, and corn are important sources of fodder. Scraps fed to pigs are called slop, and those fed to chicken are called chicken scratch.
The main crops cultivated are cereal such as millet, corn, cassava and cotton. The main animals for livestock are pigs, cattle, chickens amongst other animals. Due to the region's geographical location, there are several lakes which permit the community to practise fishing.
In regions with a subtropical climate, oil-yielding crops (e.g. soybeans), cotton, rice, tobacco, indigo, citrus, pomegranates, and some vegetables and herbs are the predominant cash crops.
|
Gases are most ideal at high temperature and what pressure?
|
[
"low",
"absolute",
"high",
"stable"
] |
A
|
Under what conditions then, do gases behave least ideally? When a gas is put under high pressure, its molecules are forced closer together as the empty space between the particles is diminished. A decrease in the empty space means that the assumption that the volume of the particles themselves is negligible is less valid. When a gas is cooled, the decrease in kinetic energy of the particles causes them to slow down. If the particles are moving at slower speeds, the attractive forces between them are more prominent. Another way to view it is that continued cooling the gas will eventually turn it into a liquid and a liquid is certainly not an ideal gas anymore (see liquid nitrogen in the Figure below ). In summary, a real gas deviates most from an ideal gas at low temperatures and high pressures. Gases are most ideal at high temperature and low pressure.
For example, terrestrial air is primarily made up of diatomic gases (around 78% nitrogen, N2, and 21% oxygen, O2), and at standard conditions it can be considered to be an ideal gas. The above value of 1.4 is highly consistent with the measured adiabatic indices for dry air within a temperature range of 0–200 °C, exhibiting a deviation of only 0.2% (see tabulation above). For a linear triatomic molecule such as CO2, there are only 5 degrees of freedom (3 translations and 2 rotations), assuming vibrational modes are not excited.
The gas is usually krypton or xenon at a few atmospheres pressure. They are applied usually to wavelengths in the 0.15–0.6 nm range. They are applicable in principle to longer wavelengths, but are limited by the problem of manufacturing a thin window capable of withstanding the high pressure difference.
The upper-level clouds lie at pressures below one bar, where the temperature is suitable for methane to condense. For pressures between one and five bars (100 and 500 kPa), clouds of ammonia and hydrogen sulfide are thought to form. Above a pressure of five bars, the clouds may consist of ammonia, ammonium sulfide, hydrogen sulfide and water.
The following table shows the specific latent heats and change of phase temperatures (at standard pressure) of some common fluids and gases.
The middle layer of the Uranian atmosphere is the stratosphere, where temperature generally increases with altitude from 53 K (−220 °C; −364 °F) in the tropopause to between 800 and 850 K (527 and 577 °C; 980 and 1,070 °F) at the base of the thermosphere. The heating of the stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons, which form in this part of the atmosphere as a result of methane photolysis. Heat is also conducted from the hot thermosphere. The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 300 km corresponding to a pressure range of 1000 to 10 Pa and temperatures of between 75 and 170 K (−198 and −103 °C; −325 and −154 °F).The most abundant hydrocarbons are methane, acetylene and ethane with mixing ratios of around 10−7 relative to hydrogen.
|
Hard igneous rocks and easily dissolved sedimentary rocks respond very differently to what natural force?
|
[
"gravity",
"weathering",
"sunlight",
"evaporation"
] |
B
|
Each type of rock weathers in its own way. Certain types of rock are very resistant to weathering. Igneous rocks tend to weather slowly because they are hard. Water cannot easily penetrate them. Granite is a very stable igneous rock. Other types of rock are easily weathered because they dissolve easily in weak acids. Limestone is a sedimentary rock that dissolves easily. When softer rocks wear away, the more resistant rocks form ridges or hills.
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus (organic matter). The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes.
Clay is a very common substance. Shale, formed largely from clay, is the most common sedimentary rock. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy.
In this series, quartz is the most stable, followed by feldspar, micas, and finally other less stable minerals that are only present when little weathering has occurred. The amount of weathering depends mainly on the distance to the source area, the local climate and the time it took for the sediment to be transported to the point where it is deposited. In most sedimentary rocks, mica, feldspar and less stable minerals have been weathered to clay minerals like kaolinite, illite or smectite.
At the same time, the soil is enriched in aluminium and potassium, by at least 50%; by titanium, whose abundance triples; and by ferric iron, whose abundance increases by an order of magnitude compared with the bedrock.Basaltic rock is more easily weathered than granitic rock, due to its formation at higher temperatures and drier conditions. The fine grain size and presence of volcanic glass also hasten weathering.
Boulder clay is an unsorted agglomeration of clastic sediment that is unstratified and structureless and contains gravel of various sizes, shapes, and compositions distributed at random in a fine-grained matrix. The fine-grained matrix consists of stiff, hard, pulverized clay or rock flour. Boulder clay is also known as either known as drift clay; till; unstratified drift, geschiebelehm (German); argile á blocaux (French); and keileem (Dutch).The term boulder clay is infrequently used for gravelly sedimentary deposits of nonglacial origin. These deposits include submarine slump and slide deposits along continental margins, lacustrine debris flow deposits consisting of pebbly mudstones, and coarse, poorly sorted, cobbly diamictons associated with the Guangxi karst, China.
|
A diet rich in calcium and what vitamin may reduce the risk of osteoporosis and related bone fractures?
|
[
"niacin",
"vitamin d",
"vitamin A",
"vitamin C"
] |
B
|
Skeletal system problems include osteoporosis, bone fractures, and ligament sprains. A diet rick in calcium and vitamin D may reduce the risk of osteoporosis and related bone fractures. Following safe practices may also reduce the risk of fractures as well as sprains.
In those who are otherwise healthy, there is little evidence that supplements have any benefits with respect to cancer or heart disease. Vitamin A and E supplements not only provide no health benefits for generally healthy individuals, but they may increase mortality, though the two large studies that support this conclusion included smokers for whom it was already known that beta-carotene supplements can be harmful. A 2018 meta-analysis found no evidence that intake of vitamin D or calcium for community-dwelling elderly people reduced bone fractures.Europe has regulations that define limits of vitamin (and mineral) dosages for their safe use as dietary supplements. Most vitamins that are sold as dietary supplements are not supposed to exceed a maximum daily dosage referred to as the tolerable upper intake level (UL or Upper Limit).
To prevent low bone density it is recommended to have sufficient calcium and vitamin D. Sufficient calcium is defined as 1,000 mg per day, increasing to 1,200 mg for women above 50 and men above 70. Sufficient vitamin D is defined as 600 IUs per day for adults 19 to 70, increasing to 800 IUs per day for those over 71. Exercise, especially weight-bearing and resistance exercises are most effective for building bone. Weight-bearing exercise includes walking, jogging, dancing, and hiking.
The World Health Organization (WHO) suggests 1.5–2 g of calcium supplements daily, for pregnant women who have low levels of calcium in their diet. Supplemental intake of C and E vitamins have not been found to reduce preterm birth rates.While periodontal infection has been linked with preterm birth, randomized trials have not shown that periodontal care during pregnancy reduces preterm birth rates. Smoking cessation has also been shown to reduce the risk.
Various animal studies have indicated that the intake of saturated fat has a negative effect on the mineral density of bones. One study suggested that men may be particularly vulnerable.
One meta-analysis reported no adverse effects of higher protein intakes on bone density. Another meta-analysis reported a small decrease in systolic and diastolic blood pressure with diets higher in protein, with no differences between animal and plant protein.High protein diets have been shown to lead to an additional 1.21 kg of weight loss over a period of 3 months versus a baseline protein diet in a meta-analysis. Benefits of decreased body mass index as well as HDL cholesterol were more strongly observed in studies with only a slight increase in protein intake rather where high protein intake was classified as 45% of total energy intake.
|
How many people die from air pollution each year?
|
[
"22 million",
"14 million",
"17 million",
"5 million"
] |
A
|
Air pollution is harmful to human beings and other living things. About 22 million people die from air pollution each year. Breathing polluted air increases the risk of developing lung diseases such as asthma and lung cancer. Breathing bad air also increases the chances of dying from other diseases. Children are most likely to be affected by air pollution. That’s because their lungs are still developing and growing. Children also take in more air for their size than adults do. Some air pollutants damage the environment as well as the health of living things. The type of damage depends on the pollutant. Air pollution can also harm the environment.
The World Health Organization considers that during 2018 approximately 3 billion people, which was more than 40% of the 2018 estimated global population, used polluting fuel sources in their residences.
The consumption of polluted water leads to many deaths. In the year 2015, 1.8 million people world wide died because of water pollution and over 1 billion people became ill. Low-income and third-world communities are especially endangered, because they often live close to industries with high emission. Hazards like waterborne pathogens and diseases spread fast in water surface bodies like rivers and are especially threatening in third-world countries without sewage- and wastewater treatment systems.
Emissions from these sources can cause respiratory disease, childhood asthma, cancer, and other health problems. A fine particulate matter such as diesel soot, which contributes to more than 3.2 million premature deaths around the world each year, is a significant problem.
The effects of inhaling particulate matter that have been widely studied in humans and animals include COVID-19, asthma, lung cancer, respiratory diseases like silicosis, cardiovascular disease, premature delivery, birth defects, low birth weight, developmental disorders, neurodegenerative disorders mental disorders, and premature death. Outdoor fine particulates with diameter less than 2.5 microns accounts for 4.2 million annual deaths worldwide, and more than 103 million disability-adjusted life-years lost, making it the fifth leading risk factor for death. Air pollution has also been linked to a range of other psychosocial problems. Particulates may cause tissue damage by entering organs directly, or indirectly by systemic inflammation. Adverse impacts may obtain even at exposure levels lower than published air quality standards deemed safe.
The risk is greatest in young people and females.Anaphylaxis leads to as many as 500–1,000 deaths per year (2.7 per million) in the United States, 20 deaths per year in the United Kingdom (0.33 per million), and 15 deaths per year in Australia (0.64 per million). Another estimate from the United States puts the death rate at 0.7 per million.
|
What substances serve as catalysts in most of the biochemical reactions that take place in organisms?
|
[
"hormones",
"enzymes",
"carbohydrates",
"iseotrops"
] |
B
|
Enzymes are involved in most of the biochemical reactions that take place in organisms. About 4,000 such reactions are known to be catalyzed by enzymes, but the number may be even higher. Enzymes allow reactions to occur at the rate necessary for life.
In biology, enzymes are protein-based catalysts in metabolism and catabolism. Most biocatalysts are enzymes, but other non-protein-based classes of biomolecules also exhibit catalytic properties including ribozymes, and synthetic deoxyribozymes.Biocatalysts can be thought of as an intermediate between homogeneous and heterogeneous catalysts, although strictly speaking soluble enzymes are homogeneous catalysts and membrane-bound enzymes are heterogeneous. Several factors affect the activity of enzymes (and other catalysts) including temperature, pH, the concentration of enzymes, substrate, and products. A particularly important reagent in enzymatic reactions is water, which is the product of many bond-forming reactions and a reactant in many bond-breaking processes.
In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperature and concentrations present within a cell. The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays and reactions between elementary particles, as described by quantum field theory.
Primary production is the production of chemical energy in organic compounds by living organisms. The main source of this energy is sunlight but a minute fraction of primary production is driven by lithotrophic organisms using the chemical energy of inorganic molecules.Regardless of its source, this energy is used to synthesize complex organic molecules from simpler inorganic compounds such as carbon dioxide (CO2) and water (H2O). The following two equations are simplified representations of photosynthesis (top) and (one form of) chemosynthesis (bottom): CO2 + H2O + light → CH2O + O2 CO2 + O2 + 4 H2S → CH2O + 4 S + 3 H2OIn both cases, the end point is a polymer of reduced carbohydrate, (CH2O)n, typically molecules such as glucose or other sugars. These relatively simple molecules may be then used to further synthesise more complicated molecules, including proteins, complex carbohydrates, lipids, and nucleic acids, or be respired to perform work. Consumption of primary producers by heterotrophic organisms, such as animals, then transfers these organic molecules (and the energy stored within them) up the food web, fueling all of the Earth's living systems.
One of the most obvious applications of catalysis is the hydrogenation (reaction with hydrogen gas) of fats using nickel catalyst to produce margarine. Many other foodstuffs are prepared via biocatalysis (see below).
Most of the structures that make up animals, plants and microbes are made from four basic classes of molecules: amino acids, carbohydrates, nucleic acid and lipids (often called fats). As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues, or on breaking them down and using them to obtain energy, by their digestion. These biochemicals can be joined to make polymers such as DNA and proteins, essential macromolecules of life.
|
The formation of an amalgam allows the metal to react with what?
|
[
"air and water",
"helium and oxygen",
"cloth and plastic",
"blood and sweat"
] |
A
|
The metals of group 13 (Al, Ga, In, and Tl) are all reactive. However, passivation occurs as a tough, hard, thin film of the metal oxide forms upon exposure to air. Disruption of this film may counter the passivation, allowing the metal to react. One way to disrupt the film is to expose the passivated metal to mercury. Some of the metal dissolves in the mercury to form an amalgam, which sheds the protective oxide layer to expose the metal to further reaction. The formation of an amalgam allows the metal to react with air and water.
Because the solubility of both silver and tin in mercury is limited and because silver is much less soluble in mercury than is tin, silver precipitates out first as silver-mercury (γ1) followed by tin in the form of tin-mercury (γ2). The set amalgam consists of unreacted gamma particles surrounded by a matrix of gamma 1 and gamma 2. The amalgamation is summarised as follows: Ag3Sn, Ag5Sn + Hg → Ag2Hg3 + Sn8Hg + Ag3Sn i.e. (γ + β) + Hg → γ1 + γ2 + γ
Cupellation is a refining process in metallurgy in which ores or alloyed metals are treated under very high temperatures and subjected to controlled operations to separate noble metals, like gold and silver, from base metals, like lead, copper, zinc, arsenic, antimony, or bismuth, present in the ore. The process is based on the principle that precious metals do not oxidise or react chemically, unlike base metals. When they are heated at high temperatures, the precious metals remain apart, and the others react, forming slags or other compounds.Since the Early Bronze Age, the process was used to obtain silver from smelted lead ores.
Metal ions have multiple roles during the reaction. Firstly it can bind to negatively charged substrate groups so they will not repel electron pairs from active site's nucleophilic groups. It can attract negatively charged electrons to increase electrophilicity.
Some reactions considered fundamental to the behavior of metal aquo ions are ligand exchange, electron-transfer, and acid-base reactions.
The molten enamel dissolves the iron oxide and precipitates cobalt and nickel. The iron acts as the anode in an electrogalvanic reaction in which the iron is again oxidised, dissolved by the glass, and oxidised again with the available cobalt and nickel limiting the reaction. Finally, the surface becomes roughened with the glass anchored into the holes.
|
A pulley changes the direction of the force t exerted by the cord without changing its what?
|
[
"magnitude",
"longitude",
"latitude",
"position"
] |
A
|
automobile axle drives a wheel, which has a much larger diameter than the axle. The MA is less than 1. (c) An ordinary pulley is used to lift a heavy load. The pulley changes the direction of the force T exerted by the cord without changing its magnitude. Hence, this machine has an MA of 1.
In a funicular, both cars are permanently connected to the opposite ends of the same cable, known as a haul rope; this haul rope runs through a system of pulleys at the upper end of the line. If the railway track is not perfectly straight, the cable is guided along the track using sheaves – unpowered pulleys that simply allow the cable to change direction. While one car is pulled upwards by one end of the haul rope, the other car descends the slope at the other end.
The tension reel has a motoring current to pull the strip taught, and the payoff reel generates to pull back against the strip. To keep these tensions constant during acceleration/deceleration of the mill, an additional current must be applied to the reels and bridles to produce the extra torque required to accelerate/decelerate them, especially when there is a large part of a coil on a reel. This is referred to as “inertia compensation”.
See tat. cord lock A lock or toggle used to fasten cords with gloved hands. Used on most mountaineering gear.
When creating a piece of Universal Gym Equipment in the 1950s, Harold Zinkin improved Jack LaLanne’s invention of the cable machine.Cable machines, also known as pulley machines, are large upright machines, either with a single pulley, or else a pulley attached to both sides. They allow an athlete to recruit all major muscle groups while moving in multiple planes. Cable machines also provide a smooth, continuous action which reduces the need for momentum to start repetitions, provide a constant tension on the muscle, peak-contraction is possible at the top of each rep, a safe means of performing negative repetitions, and a variety of attachments that allow great flexibility in the exercises performed and body parts targeted.
The friction between the ropes and the pulley furnishes the traction which gives this type of elevator its name. Hydraulic elevators use the principles of hydraulics (in the sense of hydraulic power) to pressurize an above-ground or in-ground piston to raise and lower the car (see Hydraulic elevators below). Roped hydraulics use a combination of both ropes and hydraulic power to raise and lower cars.
|
What is the name of the small bumps that contain taste buds and covers the tongue?
|
[
"lingual tonsils",
"palatine tonsils",
"papillae",
"cuticle"
] |
C
|
Figure 14.3 The Tongue The tongue is covered with small bumps, called papillae, which contain taste buds that are sensitive to chemicals in ingested food or drink. Different types of papillae are found in different regions of the tongue. The taste buds contain specialized gustatory receptor cells that respond to chemical stimuli dissolved in the saliva. These receptor cells activate sensory neurons that are part of the facial and glossopharyngeal nerves. LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012).
The exception to this are the filiform papillae that do not contain taste buds. There are between 2000 and 5000 taste buds that are located on the back and front of the tongue. Others are located on the roof, sides and back of the mouth, and in the throat.
Some people have small (<1 cm) horn-like triangular flaps of "skin" (mucosa) under their tongue. They are on each side of the frenulum (the piece of tissue connecting the bottom of the tongue to the inside of the mouth) under the tongue and run parallel next to the two distinct veins. They typically appear in pairs and may even be up to 4 or more sets, but for even those who have them only two closer to the tip are distinctly visible while the others are very minor or just small bumps. These are the "fringe-like processes" part of the "fimbriated fold". They are normal residual tissue not completely reabsorbed by the body during the development and growth of the tongue.
The glossopharyngeal nerve connects to taste buds in the posterior two thirds of the tongue. The vagus nerve connects to taste buds in the extreme posterior of the tongue, verging on the pharynx, which are more sensitive to noxious stimuli such as bitterness.Flavor depends on odor, texture, and temperature as well as on taste. Humans receive tastes through sensory organs called taste buds, or gustatory calyculi, concentrated on the upper surface of the tongue.
Nonkeratinized tissue also lines the cheeks (buccal mucosa), underside of the tongue and floor of the mouth. The lips contain both non-keratinized tissue (on the inside) and keratinized tissue on the outside, demarcated by the vermillion border. The dorsum of the tongue is keratinized and features many papillae, some of which contain taste buds.Exposure of the tooth root due to loss of keratinized tissue around the neck of a tooth is referred to as gingival recession.
The tongue is a muscular hydrostat that forms part of the floor of the oral cavity. The left and right sides of the tongue are separated by a vertical section of fibrous tissue known as the lingual septum. This division is along the length of the tongue save for the very back of the pharyngeal part and is visible as a groove called the median sulcus. The human tongue is divided into anterior and posterior parts by the terminal sulcus which is a V-shaped groove.
|
In the absence of air resistance, all falling objects accelerate at the same rate due to what force?
|
[
"gravity",
"velocity",
"weight",
"motion"
] |
A
|
What if you were to drop a bowling ball and a soccer ball at the same time from the same distance above the ground? The bowling ball has greater mass than the basketball, so the pull of gravity on it is greater. Would it fall to the ground faster? No, the bowling ball and basketball would reach the ground at the same time. The reason? The more massive bowling ball is also harder to move because of its greater mass, so it ends up moving at the same acceleration as the soccer ball. This is true of all falling objects. They all accelerate at the same rate due to gravity, unless air resistance affects one object more than another. For example, a falling leaf is slowed down by air resistance more than a falling acorn because of the leaf’s greater surface area. You can simulate the effect of air resistance on acceleration due to gravity by doing the interactive animation at this URL: http://www. science-animations. com/support-files/freefall. swf.
All other forces, especially friction and air resistance, must be absent or at least negligible. For example, if a hammer and a feather are dropped from the same height through the air on Earth, the feather will take much longer to reach the ground; the feather is not really in free-fall because the force of air resistance upwards against the feather is comparable to the downward force of gravity. On the other hand, if the experiment is performed in a vacuum, in which there is no air resistance, the hammer and the feather should hit the ground at exactly the same time (assuming the acceleration of both objects towards each other, and of the ground towards both objects, for its own part, is negligible).
However, this does not include a (non-free) fall in which air resistance produces drag forces that reduce the acceleration until constant terminal velocity is reached. At terminal velocity, the accelerometer will indicate 1 g acceleration upwards. For the same reason a skydiver, upon reaching terminal velocity, does not feel as though he or she were in "free-fall", but rather experiences a feeling similar to being supported (at 1 g) on a "bed" of uprushing air.
55 BCE) asserts that more massive bodies fall faster in a medium because the latter resists less, but in a vacuum fall with equal speed. Roman engineer and architect Vitruvius (c. 85 – c.
This led Aristotle to speculate that the rate of falling is proportional to the weight and inversely proportional to the density of the medium. From his experience with objects falling in water, he concluded that water is approximately ten times denser than air. By weighing a volume of compressed air, Galileo showed that this overestimates the density of air by a factor of forty.
If some air happens to be heavier/lighter than that in the surroundings, though, vertical motions do occur and modify the horizontal motion in turn. In nature downdrafts and updrafts can sometimes be more rapid and intense than the motion parallel to the ground. The balanced-flow equations do not contain either a force representing the sinking/buoyancy action or the vertical component of velocity.
|
The ability for a plasma membrane to only allow certain molecules in or out of the cell is referred to as what?
|
[
"selective permeability",
"periodic permeability",
"total permeability",
"moderate permeability"
] |
A
|
The plasma membrane forms a barrier between the cytoplasm inside the cell and the environment outside the cell. It protects and supports the cell and also controls everything that enters and leaves the cell. It allows only certain substances to pass through, while keeping others in or out. The ability to allow only certain molecules in or out of the cell is referred to as selective permeability or semipermeability. To understand how the plasma membrane controls what crosses into or out of the cell, you need to know its composition.
invagination The infolding of a membrane toward the interior of a cell or organelle, or of a sheet of cells toward the interior of a developing embryo, tissue, or organ, forming a distinct membrane-lined pocket. In the case of individual cells, the invaginated pocket may proceed to separate from the source membrane entirely, creating a membrane-bound vesicle within the cell, as in endocytosis. ionophore Any chemical compound or macromolecule that facilitates the movement of ions across biological membranes, or more specifically, any chemical species that reversibly binds electrically charged atoms or molecules. Many ionophores are lipid-soluble proteins that catalyze the transport of monovalent and divalent cations across the hydrophobic lipid bilayers surrounding cells and vesicles.
Nutrient media is circulated through the fibers to sustain the cells. During use, plasma is removed from the patients blood. The patient's plasma is fed into the space surrounding the fibers. The fibers, which are composed of a semi-permeable membrane, facilitate transfer of toxins, nutrients and other chemicals between the blood and the suspended cells. The membrane also keeps immune bodies, such as immunoglobulins, from passing to the cells to prevent an immune system rejection.
In comparing the two, they calculated an estimated ratio of 2:1 Mono-layer of lipids: Plasma membrane. This supported their hypothesis, which led to the conclusion that cell membranes are composed of two opposing molecular layers.
Transient vesicle fusion is driven by SNARE proteins, resulting in release of vesicle contents into the extracellular space (or in case of neurons in the synaptic cleft). The merging of the donor and the acceptor membranes accomplishes three tasks: The surface of the plasma membrane increases (by the surface of the fused vesicle). This is important for the regulation of cell size, e.g., during cell growth. The substances within the vesicle are released into the exterior.
One of the main roles of extracellular fluid is to facilitate the exchange of molecular oxygen from blood to tissue cells and for carbon dioxide, CO2, produced in cell mitochondria, back to the blood. Since carbon dioxide is about 20 times more soluble in water than oxygen, it can relatively easily diffuse in the aqueous fluid between cells and blood.However, hydrophobic molecular oxygen has very poor water solubility and prefers hydrophobic lipid crystalline structures. As a result of this, plasma lipoproteins can carry significantly more O2 than in the surrounding aqueous medium.If hemoglobin in erythrocytes is the main transporter of oxygen in the blood, plasma lipoproteins may be its only carrier in the ECF.
|
In the presence of oxygen, hydrogen can interact to make what?
|
[
"water",
"carbon",
"helium",
"acid"
] |
A
|
A pile of leaves slowly rots in the backyard. In the presence of oxygen, hydrogen can interact to make water. Gold can be stretched into very thin wires.
The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the universe up to a redshift of z = 4.Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2. Hydrogen gas is very rare in the Earth's atmosphere (around 0.53 ppm on a molar basis) because of its light weight, which enables it to escape from the atmosphere more rapidly than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface, mostly in the form of chemical compounds such as hydrocarbons and water.A molecular form called protonated molecular hydrogen (H+3) is found in the interstellar medium, where it is generated by ionization of molecular hydrogen from cosmic rays.
This excited state then decomposes to species such as hydroxyl radicals (HO. ), hydrogen atoms (H.) and oxygen atoms (O.).
The molecular hydrogen and oxygen's mutual affinity drives the fuel cell to separate the electrons from the hydrogen, to use them to power the electric motor, and to return them to the ionized water molecules that were formed when the electron-depleted hydrogen combined with the oxygen in the fuel cell. Recalling that a hydrogen atom is nothing more than a proton and an electron; in essence, the motor is driven by the proton's atomic attraction to the oxygen nucleus, and the electron's attraction to the ionized water molecule. An HFEV is an all-electric car featuring an open-source battery in the form of a hydrogen tank and the atmosphere.
This inhibits oxygen's reaching a level where it is able to stop the production of hydrogen. The third track, mainly investigated by researchers in the 1950s, is chemical or mechanical methods of removal of O2 produced by the photosynthetic activity of the algal cells.
Some oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin binds most of the hydrogen ions as it has a much greater affinity for more hydrogen than does oxyhemoglobin.
|
What galaxy is our solar system a part of?
|
[
"Centaurus",
"Andromeda",
"Bode's Galaxy",
"milky way"
] |
D
|
Compared to Earth, the solar system is a big place. But galaxies are bigger - a lot bigger. A galaxy is a very large group of stars held together by gravity. How enormous a galaxy is and how many stars it contains are impossible for us to really understand. A galaxy contains up to a few billion stars! Our solar system is in the Milky Way Galaxy. It is so large that if our solar system were the size of your fist, the galaxy’s disk would be wider than the entire United States! There are several different types of galaxies, and there are billions of galaxies in the universe.
However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups. Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a mass range between those of the very large elliptical galaxies and clusters of galaxies.Our own galaxy, the Milky Way, is contained in the Local Group of more than 54 galaxies.In July 2017 S. Paul, R. S. John et al. defined clear distinguishing parameters for classifying galaxy aggregations as ‘galaxy groups’ and ‘clusters’ on the basis of scaling laws that they followed. According to this paper, galaxy aggregations less massive than 8 × 1013 solar masses are classified as galaxy groups.
Galaxies can be described as all of the following: Astronomical object
Planetary science is the study of the assemblage of planets, moons, dwarf planets, comets, asteroids, and other bodies orbiting the Sun, as well as extrasolar planets. The Solar System has been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of the Sun's planetary system, although many new discoveries are still being made.The Solar System is divided into the inner Solar System (subdivided into the inner planets and the asteroid belt), the outer Solar System (subdivided into the outer planets and centaurs), comets, the trans-Neptunian region (subdivided into the Kuiper belt, and the scattered disc) and the farthest regions (e.g., boundaries of the heliosphere, and the Oort Cloud, which may extend as far as a light-year). The inner terrestrial planets consist of Mercury, Venus, Earth, and Mars.
As such, the starburst nature of a galaxy is a phase, and one that typically occupies a brief period of a galaxy's evolution. The majority of starburst galaxies are in the midst of a merger or close encounter with another galaxy. Starburst galaxies include M82, NGC 4038/NGC 4039 (the Antennae Galaxies), and IC 10.
The arm is between the Carina–Sagittarius Arm (the local portions of which are toward the Galactic Center) and the Perseus Arm (the local portion of which is the main outer-most arm and one of two major arms of the galaxy). Long thought to be a minor structure, namely a "spur" between the two arms mentioned, evidence was presented in mid 2013 that the Orion Arm might be a branch of the Perseus Arm, or possibly an independent arm segment.Within the arm, the Solar System is close to its inner rim, in a relative cavity in the arm's interstellar medium known as the Local Bubble, about halfway along the arm's length, approximately 8,000 parsecs (26,000 light-years) from the Galactic Center. Recently, the parallax and proper motion of more than 30 methanol (6.7-GHz) and water (22-GHz) masers in high-mass star-forming regions within a few kiloparsecs of the Sun were measured.
|
The angle at which light bends when it enters a different medium is known as what?
|
[
"bounce",
"refraction",
"frequency",
"resonance"
] |
B
|
The angle at which light bends when it enters a different medium depends on its change in speed. The greater the change in speed, the greater the angle of refraction is. For example, light refracts more when it passes from air to diamond than it does when it passes from air to water. That’s because the speed of light is slower in diamond than it is in water.
In optics, tilt is a deviation in the direction a beam of light propagates.
To describe any electromagnetic properties of a given achiral material such as an optical lens, there are two significant parameters. These are permittivity, ϵ r {\displaystyle \epsilon _{r}} , and permeability, μ r {\displaystyle \mu _{r}} , which allow accurate prediction of light waves traveling within materials, and electromagnetic phenomena that occur at the interface between two materials.For example, refraction is an electromagnetic phenomenon which occurs at the interface between two materials. Snell's law states that the relationship between the angle of incidence of a beam of electromagnetic radiation (light) and the resulting angle of refraction rests on the refractive indices, n {\displaystyle n} , of the two media (materials). The refractive index of an achiral medium is given by n = ± ϵ r μ r {\displaystyle \scriptstyle n=\pm {\sqrt {\epsilon _{r}\mu _{r}}}} .
Light is emitted from a source such as a vapor lamp. A slit selects a thin strip of light which passes through the collimator where it gets parallelized. The aligned light then passes through the prism in which it is refracted twice (once when entering and once when leaving). Due to the nature of a dispersive element the angle with which light is refracted depends on its wavelength.
The total intensity and degree of polarization are unaffected. If the path length in the birefringent medium is sufficient, the two polarization components of a collimated beam (or ray) can exit the material with a positional offset, even though their final propagation directions will be the same (assuming the entrance face and exit face are parallel). This is commonly viewed using calcite crystals, which present the viewer with two slightly offset images, in opposite polarizations, of an object behind the crystal. It was this effect that provided the first discovery of polarization, by Erasmus Bartholinus in 1669.
Rotation of light's plane of polarization may also occur through the Faraday effect which involves a static magnetic field. However, this is a distinct phenomenon that is not classified as "optical activity." Optical activity is reciprocal, i.e. it is the same for opposite directions of wave propagation through an optically active medium, for example clockwise polarization rotation from the point of view of an observer. In case of optically active isotropic media, the rotation is the same for any direction of wave propagation.
|
Whether the organism is a bacterium, plant, or animal, all living things access energy by breaking down these?
|
[
"lipid molecules",
"protein molecules",
"carbohydrate molecules",
"oxygen molecules"
] |
C
|
The Energy Cycle Whether the organism is a bacterium, plant, or animal, all living things access energy by breaking down carbohydrate molecules. But if plants make carbohydrate molecules, why would they need to break them down, especially when it has been shown that the gas organisms release as a “waste product” (CO2) acts as a substrate for the formation of more food in photosynthesis? Remember, living things need energy to perform life functions. In addition, an organism can either make its own food or eat another organism—either way, the food still needs to be broken down. Finally, in the process of breaking down food, called cellular respiration, heterotrophs release needed energy and produce “waste” in the form of CO2 gas. In nature, there is no such thing as waste. Every single atom of matter and energy is conserved, recycling over and over infinitely. Substances change form or move from one type of molecule to another, but their constituent atoms never disappear (Figure 8.20). CO2 is no more a form of waste than oxygen is wasteful to photosynthesis. Both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs light energy to build carbohydrates in chloroplasts, and aerobic cellular respiration releases energy by using oxygen to metabolize carbohydrates in the cytoplasm and mitochondria. Both processes use electron transport chains to capture the energy necessary to drive other reactions. These two powerhouse processes, photosynthesis and cellular respiration, function in biological, cyclical harmony to allow organisms to access life-sustaining energy that originates millions of miles away in a burning star humans call the sun.
Energy processing is also important to life as it allows organisms to move, grow, and reproduce. Finally, all organisms are able to regulate their own internal environments.Biologists are able to study life at multiple levels of organization, from the molecular biology of a cell to the anatomy and physiology of plants and animals, and evolution of populations. Hence, there are multiple subdisciplines within biology, each defined by the nature of their research questions and the tools that they use.
These creatures thrive despite having no access to sunlight, and it was soon discovered that they comprise an entirely independent ecosystem. Although most of these multicellular lifeforms need dissolved oxygen (produced by oxygenic photosynthesis) for their aerobic cellular respiration and thus are not completely independent from sunlight by themselves, the basis for their food chain is a form of bacterium that derives its energy from oxidization of reactive chemicals, such as hydrogen or hydrogen sulfide, that bubble up from the Earth's interior. Other lifeforms entirely decoupled from the energy from sunlight are green sulfur bacteria which are capturing geothermal light for anoxygenic photosynthesis or bacteria running chemolithoautotrophy based on the radioactive decay of uranium.
All sorts of combinations may exist in nature, but some are more common than others. For example, most plants are photolithoautotrophic, since they use light as an energy source, water as electron donor, and CO2 as a carbon source. All animals and fungi are chemoorganoheterotrophic, since they use organic substances both as chemical energy sources and as electron/hydrogen donors and carbon sources. Some eukaryotic microorganisms, however, are not limited to just one nutritional mode.
Most of the structures that make up animals, plants and microbes are made from four basic classes of molecules: amino acids, carbohydrates, nucleic acid and lipids (often called fats). As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues, or on breaking them down and using them to obtain energy, by their digestion. These biochemicals can be joined to make polymers such as DNA and proteins, essential macromolecules of life.
Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.
|
Increasing the temperature of n2 molecules increases what energy of motion?
|
[
"kinetic energy",
"compression energy",
"residual energy",
"emotional energy"
] |
A
|
Increasing the temperature increases the average kinetic energy of the N2molecules.
Even though these motions are called "internal", the external portions of molecules still move—rather like the jiggling of a stationary water balloon. This permits the two-way exchange of kinetic energy between internal motions and translational motions with each molecular collision. Accordingly, as internal energy is removed from molecules, both their kinetic temperature (the kinetic energy of translational motion) and their internal temperature simultaneously diminish in equal proportions.
Temperature usually has a major effect on the rate of a chemical reaction. Molecules at a higher temperature have more thermal energy. Although collision frequency is greater at higher temperatures, this alone contributes only a very small proportion to the increase in rate of reaction. Much more important is the fact that the proportion of reactant molecules with sufficient energy to react (energy greater than activation energy: E > Ea) is significantly higher and is explained in detail by the Maxwell–Boltzmann distribution of molecular energies.
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster, weakening the intermolecular forces between them and therefore expanding the substance.
However, the main reason that temperature increases the rate of reaction is that more of the colliding particles will have the necessary activation energy resulting in more successful collisions (when bonds are formed between reactants). The influence of temperature is described by the Arrhenius equation. For example, coal burns in a fireplace in the presence of oxygen, but it does not when it is stored at room temperature.
The molecular vibrations are harmonic (at least to good approximation), and the atoms oscillate about their equilibrium positions, even at the absolute zero of temperature. At absolute zero all atoms are in their vibrational ground state and show zero point quantum mechanical motion, so that the wavefunction of a single vibrational mode is not a sharp peak, but approximately a Gaussian function (the wavefunction for n = 0 depicted in the article on the quantum harmonic oscillator). At higher temperatures the vibrational modes may be thermally excited (in a classical interpretation one expresses this by stating that "the molecules will vibrate faster"), but they oscillate still around the recognizable geometry of the molecule.
|
Which radio frequency should you listen to if you want less noise?
|
[
"fm",
"am",
"wave",
"cb"
] |
A
|
FM radio is inherently less subject to noise from stray radio sources than AM radio. The reason is that amplitudes of waves add. So an AM receiver would interpret noise added onto the amplitude of its carrier wave as part of the information. An FM receiver can be made to reject amplitudes other than that of the basic carrier wave and only look for variations in frequency. It is thus easier to reject noise from FM, since noise produces a variation in amplitude. Television is also broadcast on electromagnetic waves. Since the waves must carry a great deal of visual as well as audio information, each channel requires a larger range of frequencies than simple radio transmission. TV channels utilize frequencies in the range of 54 to 88 MHz and 174 to 222 MHz. (The entire FM radio band lies between channels 88 MHz and 174 MHz. ) These TV channels are called VHF (for very high frequency). Other channels called UHF (for ultra high frequency) utilize an even higher frequency range of 470 to 1000 MHz. The TV video signal is AM, while the TV audio is FM. Note that these frequencies are those of free transmission with the user utilizing an old-fashioned roof antenna. Satellite dishes and cable transmission of TV occurs at significantly higher frequencies and is rapidly evolving with the use of the high-definition or HD format.
At the lowest frequencies, from about 0.1 Hz to 10 Hz, ocean turbulence and microseisms are the primary contributors to the noise background. Typical noise spectrum levels decrease with increasing frequency from about 140 dB re 1 μPa2/Hz at 1 Hz to about 30 dB re 1 μPa2/Hz at 100 kHz. Distant ship traffic is one of the dominant noise sources in most areas for frequencies of around 100 Hz, while wind-induced surface noise is the main source between 1 kHz and 30 kHz.
Broadcast engineers in North America usually line up their audio gear to nominal reference level of 0 dB on a VU meter aligned to +4dBu or -20dBFs, in Europe equating to roughly +4 dBm or -18 dBFS. Peak signal levels must not exceed the nominal level by more than +10 dB.Broadcast audio as a rule must be as free as possible of Gaussian noise, that is to say, it must be as far from the noise floor, as is reasonably possible considering the storage or transmission medium. Broadcast audio must have a good signal-to-noise ratio, where speech or music is a bare minimum of 16db above the noise of the recording or transmission system. For audio that has a much poorer signal-to-noise ratio (like cockpit voice recorders), sonic enhancement is recommended.
36 MHz: aircraft and water-craft (odd channels for aircraft only) 29 MHz: general use 27 MHz: light electric aircraft, general use 2.400-2.485 GHz: 13-cm UHF band Spread Spectrum band for general use (ACMA references available at )
The professional models transmit in VHF or UHF radio frequency and have 'true' diversity reception (two separate receiver modules, each with its own antenna), which eliminates dead spots (caused by phase cancellation) and the effects caused by the reflection of the radio waves on walls and surfaces in general. (See antenna diversity). Another technique used to improve the sound quality (actually, to improve the dynamic range), is companding.
Natural background noise increases as frequency decreases, so a lot of radiated power is required to overcome it. Worse, small antennas (relative to a wavelength) are inherently inefficient. This implies high transmitter powers and very large antennas covering square kilometres.
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What form of radiation is the energy emitted by the sun?
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[
"seismic",
"magnetic",
"thermal",
"electromagnetic"
] |
D
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Figure 8.11 The sun emits energy in the form of electromagnetic radiation. This radiation exists at different wavelengths, each of which has its own characteristic energy. All electromagnetic radiation, including visible light, is characterized by its wavelength.
Nuclear particles like protons and neutrons are not destroyed in fission and fusion processes, but collections of them can have less mass than if they were individually free, in which case this mass difference can be liberated as heat and radiation in nuclear reactions (the heat and radiation have the missing mass, but it often escapes from the system, where it is not measured). The energy from the Sun is an example of this form of energy conversion. In the Sun, the process of hydrogen fusion converts about 4 million tonnes of solar matter per second into electromagnetic energy, which is radiated into space.
This caveat also applies to UV, even though almost all of it is not ionizing, because UV can damage molecules due to electronic excitation, which is far greater per unit energy than heating effects.Infrared radiation in the spectral distribution of a black body is usually considered a form of heat, since it has an equivalent temperature and is associated with an entropy change per unit of thermal energy. However, "heat" is a technical term in physics and thermodynamics and is often confused with thermal energy. Any type of electromagnetic energy can be transformed into thermal energy in interaction with matter.
In fact, due to the thick, highly reflective cloud cover, the total solar energy received by the surface of the planet is less than that of the Earth, despite its proximity to the Sun. Sulfuric acid is produced in the upper atmosphere by the Sun's photochemical action on carbon dioxide, sulfur dioxide, and water vapour. Ultraviolet photons of wavelengths less than 169 nm can photodissociate carbon dioxide into carbon monoxide and monatomic oxygen.
Having exhausted the supply of hydrogen at its core, it has cooled and expanded; now having 31 times the radius of the Sun. It is radiating 274 times the Sun's luminosity from its swollen photosphere at an effective temperature of 4,189 K. == References ==
An important fusion process is the stellar nucleosynthesis that powers stars, including the Sun. In the 20th century, it was recognized that the energy released from nuclear fusion reactions accounts for the longevity of stellar heat and light. The fusion of nuclei in a star, starting from its initial hydrogen and helium abundance, provides that energy and synthesizes new nuclei. Different reaction chains are involved, depending on the mass of the star (and therefore the pressure and temperature in its core).
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What is the suns innermost layer called?
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[
"core",
"surface",
"solar",
"flare"
] |
A
|
The core is the Sun's innermost layer. The core is plasma. It has a temperature of around 15 million degrees Celsius (C). Nuclear fusion reactions create the immense temperature. In these reactions, hydrogen atoms fuse to form helium. This releases vast amounts of energy. The energy moves towards the outer layers of the Sun. Energy from the Sun's core powers most of the solar system.
The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth. The Maunder minimum, for example, is believed to have caused the Little Ice Age phenomenon during the Middle Ages.At the center of the Sun is the core region, a volume of sufficient temperature and pressure for nuclear fusion to occur. Above the core is the radiation zone, where the plasma conveys the energy flux by means of radiation.
The stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest layer of the five layers of the epidermis, the external covering of skin in mammals. The stratum basale is a single layer of columnar or cuboidal basal cells. The cells are attached to each other and to the overlying stratum spinosum cells by desmosomes and hemidesmosomes.
The stratosphere () is the second layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air high in the sky and the cool layers of air in the low sky, close to the planetary surface of the Earth. The increase of temperature with altitude is a result of the absorption of the Sun's ultraviolet (UV) radiation by the ozone layer. The temperature inversion is in contrast to the troposphere, near the Earth's surface, where temperature decreases with altitude.
The outer layers of Earth are divided into the lithosphere and asthenosphere. The division is based on differences in mechanical properties and in the method for the transfer of heat. The lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperature gradient.
Main sequence stars are distinguished by the primary energy-generating mechanism in their central region, which joins four hydrogen nuclei to form a single helium atom through thermonuclear fusion. The Sun is an example of this class of stars. Once stars with the mass of the Sun form, the core region reaches thermal equilibrium after about 100 million (108) years and becomes radiative. This means the generated energy is transported out of the core via radiation and conduction rather than through mass transport in the form of convection.
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