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 increase in gill size?
A) The young of these animals are much more active than the adult, which leads to a higher BMR (basal metabolic rate) and, therefore, a higher need for oxygen.
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 BMR.
D) Relative to their surface area, the young have more body volume in which they can store oxygen for long periods of time.

Question

Quizplus · Accepted Answer

As the animal grows larger, its volume increases faster than its surface area, making it harder for oxygen to diffuse across the gills. Therefore, the gills need to grow larger in order to provide sufficient surface area for oxygen exchange. Option A is not correct as it incorrectly assumes that the young are more active than adults. Option C is also not correct as it is not related to the growth of gills. Option D is also not correct as it suggests an incorrect mechanism for storing oxygen in the body.

Some Animals Have No Gills When Young, but Then Develop