This is found in cell membranes and protect the cell or organelles by allowing/not allowing molecules to enter. what is it?

Answer is membrane protein

Plasma membrane or cell membrane is made of lipoprotein (lipid and protein). The structure of the plasma membrane is based on the fluid mosaic model which gives basic description of the structure and behavior of membranes. The plasma membrane is a mosaic of phospholipids, cholesterol and proteins. Many proteins can move within the plasma membrane through membrane diffusion.  The membrane proteins regulates the coming and going of substances into and out of the cell.

Phospholipid

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.