Many substances, such as cholesterol, bind to on the cell membrane, triggering endocytosis. a) active sites b) receptor sites c) import vesicles d) cholesterol pockets

Correct B). Receptor sites

The cell membrane is made up of phospholipid and cholesterol. The main function of cholesterol molecule is to provide extra support to the cell, it is more hard than other lipids in the membrane. It helps to immobilize some lipid molecules around them. These substances bind on the receptor sides of the cell membrane and help in the transfer of molecule across the membrane.

Hence, the correct answer would be option B.

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.