Question

Animals breathe oxygen and give out carbon dioxide.
(a) True
(b) False

Answer 1

Hint: On earth existence of life is possible only in the presence of oxygen gas. This gas is synthesized and released by the green plants during preparing their own food for which it uses carbon dioxide gas. This oxygen released by the plants is taken in by the animals for respiration to release carbon dioxide back into the atmosphere.

Complete answer:
Yes, it is true that animals breathe oxygen and give out carbon dioxide; this is done in the process of respiration. When we inhale or breathe in, we pull air mainly containing nitrogen and oxygen into our lungs, and whenever we exhale or breathe out, we mostly release carbon dioxide. In the process, carbon dioxide is produced as a waste product that is needed to be removed. For being alive animals and plants need oxygen. During the process of respiration when an animal breathes, it takes in oxygen gas from the atmosphere and releases carbon dioxide gas back into the atmosphere from the animal’s body. During cellular respiration, this carbon dioxide is released as the waste product produced by the animal's cells.
-Cellular respiration takes place in individual cells where exchange of gases between the cell and blood capillary occurs.
-Here oxygen is diffused into the cells from the blood capillaries and simultaneously carbon dioxide from the cells moves into the blood through which it is taken to the lungs to get released into the atmosphere.
-The oxygen in cells is used to burn food to get energy released as ATP. During the process water and carbon dioxide are produced as waste products.
-Plants make their own food by the process of photosynthesis and release oxygen gas as end or waste products of the process.
 -The plants or producers take sunlight
and combine carbon dioxide ($CO_2$) and water ($H_2$O) to produce glucose ($C_{6}H_{12}O_{6}$) and oxygen gas ($O_2$).

So, the correct answer is, 'True'.

Note:
-The plants take in carbon dioxide and release oxygen by the process of photosynthesis and
through the stomatal opening of their leaves.
-The gas exchange is mainly important for the process of respiration which involves the uptake of oxygen ($O_2$) and release of carbon dioxide ($CO_2$) gases.
-In animals the gases are continuously consumed and produced by cellular and metabolic reactions, so an efficient system for gas exchange between, the interior of the cells and the external environment is necessary.