Why do muscle cells need to have many mitochondria?

Which of the following cells synthesize and secrete bone matrix?

Earthworms have a type of movement in which rhythmic waves of muscle contractions are produced from head to tail. This movement is called _____.

A sprinter usually has a ______ proportion of ________ muscles.

The skeleton which consists of fluid held under pressure that gives the hydra its body shape and support for muscle action is called ______.