What factors affect the rate of transport of molecules across cell membrane - Essay Example

Diffusion is the movement of particles from an area of high to low concentration. It allows transportation of substances into and out of the cell (Wright 2000, p 12). Active transport is the movement of substances against a concentration gradient. It requires energy because it takes place against a concentration gradient. It explains why mitochondria are usually present when active transport takes place (Wright 2000, p 12). Osmosis is a special type of diffusion that takes place in solutions only (Wright 2000, p.12). Phagocytosis the process through which some cells such as the white blood cells take in substances (Wright 2000, p 12).

The cell membrane is described as semi permeable or selectively permeable because it lets some substances to pass through but not all (Wright 2000, p 12). Four major factors determine the rate at which molecules pass through a cell membrane (Kent 1998, p3).The first one is the size of the molecule (Kent 1998, p. 3). Large sized molecules cannot enter or leave the cell. An example of a large molecule is proteins that are too large to squeeze through the molecules that make up the cell membrane.

The smaller the size of the molecule the faster it will pass through (Lippincott 2002, p 11). The epithelial cells that cover the villus have carriers that absorb specific nutrients (Sherwood 2012, p. 467). The second factor is the solubility of the molecule in fats or lipids. As seen in Fig 2, the cell membrane is made up of thin layers of phospholipids. The molecules that can dissolve in them will be able to pass quickly. A good example is the fast absorption of ethanol by the stomach and intestinal walls (Kent 1998, p38).

When the cell membrane contains more unsaturated fatty acids, it makes it fluid like. This increases the rate of active transport. The third factor is the electrical charge of ions and molecules (Kent 1998, p.38). The cell membrane through which the substances are expected to pass