The cell membrane is composed of fat and protein molecules and is a vital cell boundary because it regulates what gets in and out of the cell. The fatty acids in its two-layered structure define the boundary between the watery cell cytoplasm and the watery extracellular fluid. Protein structures in this membrane provide for communication and transport between the interior and exterior of the cell. Various carbohydrate units attach to the protein molecules embedded in cell membrane, which serve as recognition sites for other chemical messengers traveling throughout the body. Antioxidant nutrients protect the unsaturated fatty acids that make up this membrane from oxidation and destruction of the cell

Pinocytosis:

It is a process in which a cell takes up water. Tiny pockets along the cell membrane, and then fill with liquid. Those tiny pockets then break off into the cell to form tiny vacuoles filled with water.

Phagocytosis:

It is a process in which cells take in large particles, clumps of food and even other cells! In phagocytosis, extensions of cytoplasm surround and engulf the object that it is trying to take in. A type of a single celled organism that uses this process to capture its food is the Ameba.