A: A certain amount of energy (the activation energy) is needed for the reaction to take place. At higher temperatures, there is more kinetic energy and the increased rate of random collisions between molecules increases the probability that they will collide in the right way to react. Thus, (A) correctly characterizes this relationship. (B) is incorrect because there is more kinetic energy at higher temperatures, not at lower temperatures, and because increased kinetic energy actually raises the likelihood that the substrate will bind to the enzyme. (C) is incorrect because 30°C is actually a higher temperature than 37°C, so it makes no sense to say that the protein “denatured due to excess heat.” (D) is incorrect because substrate concentration remains constant, according to the question stem.
C: DPIP acts as a substitute for NADP+ in photosynthesis. During photosynthesis, DPIP is reduced and becomes colorless, which results in an increase in light transmittance. According to the data, an increase in light transmittance over time is found for the tube exposed to light only. The correct answer is (C). Choice A is incorrect because DPIP changes from blue to clear when reduced during photosynthesis. Choice B is incorrect because the tube exposed to light only had the highest rate of photosynthesis (increasing percent transmittance). Choice D is incorrect because the solution in all four tubes was blue at time 0.
C: The pharmacist’s dilution of albumin was correct: when a solution of 25% albumin is diluted to contain five times as much water, it will have one-fifth of the original concentration, or 5% albumin. However, the pharmacist should have used sterile saline solution instead of the distilled water, to ensure that there was an adequate concentration of NaCl. Because the resulting solution was hypotonic to the red blood cells, water from the solution osmosed into the cells, causing them to burst, as in (C). (A) and (B) are incorrect because the pharmacist did not err in his dilution of the albumin. (D) is incorrect because the solution is hypo- tonic to the red blood cells, not hypertonic.
B: Because the lac− cells contain everything necessary to construct enzymes that can ferment lactose except for the DNA with the lac+ genes, the only cells that would be adversely affected would be those incubated with extract B, which loses those genes due to the action of the DNases. Because those cells would be unable to ferment lactose, they would appear as colorless. (B) is thus correct. (A) is incorrect because the lac− cells contain all the proteins and amino acids necessary to construct lactose-fermenting enzymes, provided they have the proper genes (which they can get from extract A), so they would appear blue. (C) is incorrect because the lac− cells contain all the RNA molecules and nucleotides necessary to transcribe and translate the lactose-fermenting enzymes, provided they have the proper genes (which they can get from extract C), so they would also appear blue. (D) is incorrect because the cells incubated with extract B will appear colorless, as explained above.
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