A facultative anaerobe is an organism that ________.
Answer: B
Correct answer: grows with or without oxygen, but better with it
A facultative anaerobe respires aerobically when oxygen is present and switches to fermentation or anaerobic respiration when it is not. Escherichia coli is the standard example, and in a thioglycolate tube such organisms grow throughout while clustering near the top.
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Many coenzymes are
Answer: B
Correct answer: vitamins
Many coenzymes are derived from vitamins, which is precisely why vitamins are needed in the diet in such small amounts: NAD from niacin, FAD from riboflavin, coenzyme A from pantothenate, TPP from thiamine. Metal ions are cofactors but not coenzymes, which are organic.
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_________is another term for biosynthesis.
Answer: B
Correct answer: anabolism
Anabolism is biosynthesis: small precursors assembled into the macromolecules the cell needs, using the energy and reducing power that catabolism supplies. Metabolism is the two halves together.
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An organic nutrient essential to an organism’s metabolism that it cannot synthesise for itself is termed a/an:
Answer: C
Correct answer: growth factor
A growth factor is an organic compound - a vitamin, an amino acid, a purine or pyrimidine - that an organism must have but cannot make for itself, so it has to be supplied in the medium. Trace elements and micronutrients are inorganic and needed only in minute amounts.
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Which of the following nucleoside diphosphates is used most often in carbohydrate anabolism?
Answer: A
Correct answer: Uridine diphosphate
UDP is the usual carrier in carbohydrate biosynthesis: sugars are activated as UDP-glucose, UDP-galactose and the like before being transferred to a growing chain. Activation is necessary because the transfer itself is thermodynamically unfavourable, and the UDP leaving group is what pays for it.
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An apoenzyme is where the _____is located.
Answer: D
Correct answer: active site
The apoenzyme is the protein part of a conjugated enzyme, and it carries the active site - the pocket whose shape and chemistry determine which substrate is bound. The non-protein cofactor or coenzyme completes it; apoenzyme plus cofactor is the active holoenzyme.
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An enzyme
Answer: D
Correct answer: is heat and pH labile
Enzymes are proteins, and their activity depends on a precise three-dimensional shape, so they are denatured by heat and by pH extremes. The other statements are all false: an enzyme is highly specific for its substrate, and it is neither consumed by the reaction nor built into the products - which is why a small amount can turn over a great deal of substrate.
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Anoxygenic photosynthetic bacteria oxidize
Answer: C
Correct answer: sulfide
Anoxygenic photosynthesis uses an electron donor other than water. Hydrogen sulfide is the commonest, oxidised to elemental sulfur and then sulfate. Because H2S gives up electrons more readily than water does, only one photosystem is needed - and no oxygen is produced.
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In the passive diffusion, solute molecules cross the membrane as a result of
Answer: A
Correct answer: concentration difference
Passive diffusion needs no carrier and no energy: molecules simply move down their concentration gradient until the two sides are equal. The gradient is the whole driving force, which is why the rate falls as equilibrium is approached and why nothing can be accumulated inside the cell this way.
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In a viable plate count, each ___represents a ___from the sample population.
Answer: B
Correct answer: colony, cell
The assumption behind a viable plate count is that each colony grew from a single cell that could reproduce. So counting the colonies and multiplying by the dilution gives the number of viable cells in the original sample - and the result is reported as colony-forming units, since a clump would also give one colony.
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