The substance secreted by corals that composes their hard skeleton.

calcium carbonate

A coral reef is made of thin layers of calcium carbonate

Massive reef structures are formed when each individual stony coral organism—or polyp—secretes a skeleton of calcium carbonate.

Explanation:

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.

i'm guessing this is from edg enuity so the answers would be, from top to bottom,

theodor schwann

matthias schleiden

robert hooke

rudolph virchow

anton van leeuwenhoek