How do animals obtain nitrogen for use in synthesizing proteins?

• A. By photosynthesizing nitrogen compounds from sunlight and water
• B. By converting atmospheric nitrogen into ammonia through nitrogen fixation
• C. By consuming plants or other organisms that contain nitrogenous compounds
• D. By directly absorbing nitrogen gas (\(N_2\)) from the atmosphere

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the role of nitrogen in biological systems. Nitrogen is a key element in amino acids, which are the building blocks of proteins. Animals need nitrogen to synthesize proteins and other nitrogen-containing molecules.
2. Step 2: Recognize that animals cannot directly use atmospheric nitrogen (\(N_2\)). Atmospheric nitrogen is highly stable and requires specific processes, such as nitrogen fixation, to be converted into a usable form. However, animals lack the ability to perform nitrogen fixation.
3. Step 3: Learn how nitrogen enters the food chain. Plants absorb nitrogen from the soil in the form of nitrate (\(NO_3^-\)) or ammonium (\(NH_4^+\)), which are products of nitrogen fixation carried out by bacteria. These nitrogen compounds are incorporated into plant tissues.
4. Step 4: Understand how animals obtain nitrogen. Animals consume plants or other organisms (such as herbivores or carnivores) that contain nitrogenous compounds, such as proteins and nucleic acids. These compounds are broken down during digestion to release nitrogen for use in the animal's body.
5. Step 5: Clarify why other options are incorrect. Animals do not photosynthesize nitrogen compounds, as photosynthesis is a process specific to plants and some microorganisms. Additionally, animals cannot directly absorb nitrogen gas (\(N_2\)) from the atmosphere because they lack the enzymes required to break its strong triple bond.