Some animals have no gills when young, but then develop gills that grow larger as the animal grows larger. What is the reason for this trend?
A) The young of these animals are much more active than the adult.
B) Relative to their volume, the young have more surface area across which they can transport all the oxygen they need.
C) The young have a higher basal metabolic rate.
D) Relative to their surface area, the young have more volume in which they can store oxygen for long periods of time.

Question

Quizplus · Accepted Answer

The development of gills that grow larger as the animal grows larger could be due to the fact that when young, these animals have more surface area relative to their volume, which allows for efficient transport of oxygen through diffusion. However, as they grow larger, their volume increases faster than their surface area, making it more difficult to obtain sufficient oxygen through diffusion alone. Development of gills helps to increase the surface area available for oxygen exchange, enabling the larger body to be adequately supplied with oxygen.

Some Animals Have No Gills When Young, but Then Develop