Question

Which one of the following statements is incorrect?

• A. The principle of countercurrent flow facilitates efficient respiration in gills of fishes
• B. The residual air in lungs slightly decreases the efficiency of respiration in mammals
• C. The presence of non-respiratory air sacs, increases the efficiency of respiration in birds
• D. In insects, circulating body fluids serve to distribute oxygen to tissues

Answer 1

The correct option is C. The residual air in lungs slightly decreases the efficiency of respiration in mammals.

Option (C):

Respiration in mammals:

1. The amount of gas remaining in the lungs is considered as residual volume of the gas in the individual.
   
2. Variations in level of inspiratory and expiratory gases is bridged by this residual volume and hence it does not affect the respiratory efficiency.

Explanation for the wrong options:

Option (A):

The circulating body fluid in the insects contains hemocoel as the pigment and it has the ability to distribute the oxygen throughout the body of the insect. The respiratory gasses move towards the tissues of the body.

Option (B):

1. Gills act as the respiratory organs in fishes.
   
2. The countercurrent mechanism in the gills helps with the uptake of dissolved oxygen from water.
   
3. This process facilitates effective exchange of gasses. ​

Option (D):

1. The air sacs are responsible for helping with the flight of birds.
   
2. The non-respiratory air sacs are responsible for inducing respiratory efficiency. ​