What can we infer if we see a large number of mitochondria in a cell?

It means the cell has a high metabolic demand.

Explanation:

A high metabolic demand means that the cell requires a large amount of energy released in the process called cellular respiration. The mitochondria are where most of the energy of the cell is made.

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation:

and after water is usually warmed by the sun the water temperature raises and then evaporates .