Question

we (humans and other heterotrophs) get nitrogen by

eating plants and animals.

\fixing\ it from the atmosphere.

respiration.

photosynthesis.

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Explanation:

• Humans and other heterotrophs cannot fix nitrogen from the atmosphere (only certain bacteria can do that).
• Respiration is the process of releasing energy from food, not for obtaining nitrogen.
• Photosynthesis is a process used by autotrophs (like plants) to make food using sunlight, carbon - dioxide and water, not relevant for heterotrophs' nitrogen uptake.
• Heterotrophs get nitrogen by consuming plants and animals which have incorporated nitrogen into their biological molecules (such as proteins) through various biological processes.

Answer:

eating plants and animals.