The Plasma Membrane
Regulates Passage of Molecules into and out of Cells
The Phospholipid Bilayer
Channel Proteins: Channel proteins have a channel that allows molecules to move across the membrane
Carrier Proteins: Carrier proteins combine with a substance and help it move across the membrane
Cell Recognition Proteins: Cell Recognition Proteins are glycoproteins that recognize foreign invaders
Receptor Proteins: Receptor proteins have a binding site for specific molecules. The binding of this molecule causes the protein to change shape and cause a cellular reaction.
Enzymatic Proteins: Enzymatic proteins carry out metabolic reactions directly
Junction Proteins: Junction Proteins link cells together
Another form of active transport is bulk transport. Bulk transport occurs when fluid or particles are brought into or out of a cell by vacuole formation. Bulk transport into a cell is called endocytosis. Bulk transport out of the cell is called exocytosis. Phagocytosis is bulk transport of solids into a cell, and pinocytosis is the transport of liquids into a cell.
Osmosis is the movement of water from a higher concentration to a lower concentration through a semi-permeable membrane. A hypotonic solution has a lower concentration of solutes outside the cell, and a higher concentration of solutes inside of the cell. Water floods into the cell and the cell bursts. A hypertonic solution has a higher concentration of solutes outside the cell, and a lower concentration of solutes inside of the cell. Water floods from the cell, and the cell shrivels up. In an isotonic solution, the concentration of solutes inside and outside of the cell are the same. The cell stays the same.