The animal plasma membrane is a layer of phospholipids that is entwined with cholesterol and proteins. Cholesterol makes up a small part of the cell membrane's mass and it is present in every cell of the body. Cholesterol maintains the integrity of the cell membrane. It assists in the immobilization of the outer surface of the cell membrane and it reduces the permeability of the membrane to most biological molecules. Cholesterol also perform roles in cell signaling, maintaining fluidity and protecting important proteins in the membrane.
Biotic mean alive, so we can cut off the first 2 easily. Aquatic birds eat frogs, so that one is safe for now. A decrease in something parasitic usually helps the population, so D is out too. The only one left is C.
