SAT Subject Biology Practice Question 440: Answer and Explanation

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Question: 440


Nitrogen Cycle

Can both animals and plants obtain their nitrogen from the atmosphere?

A. Yes, both animals and plants take in nitrogen during respiration.
B. Yes, most of the nitrogen in the cycle is in the atmosphere.
C. No, only plants can take in nitrogen from the atmosphere.
D. No, they must consume it through eating or uptake from the soil.
E. No, they must obtain it through symbiotic relationships.

Correct Answer: D


D Looking at the diagram, we see that plants take up nitrogen from the soil or obtain it through nitrogen-fixing bacteria in their roots, and animals obtain nitrogen by eating plants. Choice A is true; animals and plants do take in nitrogen during respiration. However, choice A should be eliminated, because this nitrogen is in a form that is not usable by animals and plants. Choice B is true but doesn't really answer the question and should be eliminated. Choice C is false; plants cannot take nitrogen directly from the atmosphere. It must first be fixed by symbiotic root bacteria or converted into ammonia. Choice E is true for plants but not for animals, and can therefore be eliminated.

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