Keep in mind that total energy in the beginning and after work remains the same according o thermodynamics theory that energy can't be created or destroyed.
Explanation:
Conversion of energy from one form to another is not 100% efficient. Even the transfer of energy from one object to another (work) is not 100% efficient. This also applies to cells. The inefficiencies are lost as heat energy. Examples of such work in the cells include active transport by cell membrane protein channels, metabolic pathways, and etcetera. Some energy in the hydrolysis of ATP to power these biochemical activities is lost as heat which is part of the reason we remain warm. This energy ends up being lost into the environment as heat (e.g even from sweating).
The fact that whales have a pelvis even though one is not required for marine life helps confirm that whales were descendants of land mammals. I hope this helps!
