Question

How do animals get their nitrogen?
A. By absorbing nitrogen gas through the skin
B. By eating carbohydrates like sugars and starch
C. From nitrates in their drinking water
D. By eating plants and other animals

Answer 1

Hint: Nitrogen is necessary for all living organisms. Most plants fulfill the requirement of nitrogen from the soil or water in which they live. The food web is a series of organisms, in which one organism can eat the other and be eaten by many different organisms. A producer (green pants) can prepare their own food by the process of photosynthesis whereas consumers (herbivores, carnivores and omnivores) depend on others for their food.

Complete answer:
Air is a mixture of several gases such as oxygen, nitrogen, carbon dioxide and inert gases. Our atmosphere has 78% nitrogen gas. Nitrogen is an important constituent of all living organisms as part of proteins, chlorophyll, nucleic acid and vitamins. Plants and animals cannot get their Nitrogen directly from our atmosphere.
Nitrogen-fixing bacteria (present in the soil and in the root nodules of leguminous plants) and blue-green algae fix the nitrogen from the atmosphere and then convert them into compounds of nitrogen which go into the soil.
The plants absorb the nitrogen compounds from the soil with the help of their roots. The plants convert the nitrogen compounds into plant proteins and several other organic compounds which build up the body of plants.
The plants are then eaten by animals as food. In the animal body, plant protein is converted into animal proteins and other organic compounds which make up their body. Some animals also eat other animals as food. They get their nitrogen by eating other animals.
When plants and animals die, the complex nitrogenous compounds present in their bodies are decomposed and converted into simple nitrogen compounds. This is done by certain bacteria and fungi (decomposers). It was again used by plants. As a result, the percentage of nitrogen in the atmosphere always remains constant.
The continuous circulation of nitrogen elements between living things and surroundings is known as the nitrogen cycle.
So, from the above discussion, it is clear that the correct option is “by eating plants and other animals”.
So, the correct answer is “Option D”.

Note:
Nitrogen fixing bacteria (Rhizobium) and blue green algae fixes the nitrogen gas from the atmosphere which is then available to plant. The plant absorbs nitrogen from soil through the roots. Animals get their nitrogen by consuming plants and other animals.