What factor is known to constrain animal body shape and size?

Question

Quizplus · Accepted Answer

Oxygen diffusion rate is known to constrain animal body shape and size. This is because oxygen must diffuse across the surface of the body to reach cells for respiration, and larger or more complex bodies can have a harder time efficiently absorbing enough oxygen. Access to water, atmospheric pressure, and nitrogen availability may all be important environmental factors for animals, but they are not known to be primary constraints on body shape and size in the same way as oxygen diffusion rate.

What Factor Is Known to Constrain Animal Body Shape and Size