Bio-1

Cell Membrane

The cell membrane functions regulate the movement of substances into and out of the cell by process of cell transport. In this cell transport, there are 7 total processes known as: Passive Transport, Active Transport, diffusion, osmosis, facilitated diffusion, ion channel, and endocytosis + exocytosis. Cell membranes act as barriers to most, but not all, molecules. Development of a cell membrane that could allow some materials to pass while constraining the movement of other molecules was a major step in the evolution of the cell. Cell membranes are differentially (or semi-) permeable barriers separating the inner cellular environment from the outer cellular (or external) environment.

Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells. Some substances can cross the cell membrane without any input of energy by the cell in a process known as Passive transport. Passive Transport requires no energy from the cell.

The simplest type of passive transport is diffusion. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. This difference in the concentration of molecules across a distance is called a concentration gradient. Cell membranes allow some molecules to pass through, but not others. The simple diffusion of a molecule across a cell membrane depends on the size and type of molecule and on the chemical nature of the membrane. Molecules that can dissolve in lipids may pass directly through the membrane by diffusion. So diffusion and concentration gradients causes’ passive transport.

Passive transport also includes osmosis, facilitated diffusion, and ion channel. Osmosis is a process by which water molecules diffuse across the cell membrane from an area if higher concentration to an area of lower concentration. Because water is moving from a higher to lower concentration, osmosis does not require cells to expand energy. Therefore, osmosis...