SAT Subject Biology Practice Question 427: Answer and Explanation

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Question: 427

17. Unfertilized frog oocytes were bathed in a neutral, isotonic solution (Frog Ringer's solution) to prevent changes in volume due to osmosis. The Frog Ringer's solution was supplemented with radiolabeled amino acids. A sample of oocytes was taken every 30 minutes and assayed for radioactivity.

At Time 1, the oocytes were fertilized. Samples were taken at five-minute intervals after fertilization and assayed for radioactivity. The results are presented in the graph below.

Based on the results of the experiment, the process most likely occurring after fertilization is

A. DNA replication
B. organogenesis
C. protein synthesis
D. RNA transcription
E. endocytosis

Correct Answer: C


C Of the choices available, you should be able to eliminate choice E (endocytosis) first. There is no evidence to support this. As for the remaining choices, be careful not to come to conclusions too quickly based on your prior knowledge. In other words, you know that after fertilization occurs the zygote undergoes rapid cell division. This means that DNA will be replicated, RNA will be transcribed, proteins will be synthesized, and ultimately, organogenesis will occur. So in effect, choices A, B, C, and D are all occurring. The question, however, asks specifically for the process that is most likely occurring based on the results of the experiment. Because the experiment measures the amount of a radiolabeled amino acid present in the cells after fertilization, it is most directly measuring the rate of protein synthesis, making C a better choice than the others.

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