Question

In external respiration,
A. Food is broken down and oxygen is absorbed.
B. Food is broken down and carbon dioxide is produced.
C. Oxygen is ejected and carbon dioxide is adsorbed.
D. None of the above.

Answer 1

Hint: External respiration is actually the breathing process, in which oxygen is taken into by inhalation and carbon-dioxide is expelled by exhalation.

Complete answer:
Respiration is the process of obtaining energy by combining oxygen and glucose, and release of carbon-di-oxide, water and ATP.
Respiration is of three types. These are: Internal respiration, External respiration and cellular respiration.
External Respiration is actually the breathing process that is the gaseous exchange between the external environment and the blood stream. In humans and other mammals, oxygen is taken into the body by lungs while in some other animals it occurs by diffusion across the surface of the body. The gaseous exchange between the plants and the external environment takes place through the leaves.
From the above information it is clear that the breakdown of food is not involved in the process of external respiration. In this process oxygen is taken from the external environment and carbon dioxide is expelled to the external environment. So, the given option A." Food is broken down and oxygen is absorbed." and B."Food is broken down and carbon dioxide is produced." are not correct.
On the other hand, oxygen is taken into by inhalation and carbon-dioxide is expelled by exhalation. So, the given option C. “oxygen is ejected and carbon dioxide is adsorbed” is also wrong.

Hence, the option D. "None of the above." is the right answer.

Note: Though carbon dioxide is produced by the breakdown of food, this process is not a part of external respiration. So, the option B. can’t be the right answer.