- Diffusion:
- This involves molecular movement of solutes, with the direction being determined by relative concentrations. The factors that affect the rate are the size of the gradient, molecular size, charge, and lipid solubility.
- The substances involved for all cells are inorganic ions and lipid-soluble materials. Osmosis is a diffusion mechanism involved in the movement of water molecules toward the solution containing relatively higher solute concentrations. To accomplish this, a membrane is required. Factors that affect the rate are the concentration of the gradient and the opposing osmotic or hydrostatic pressure. The substance involved for all cells is water only.
- Filtration:
- This involves movement of water, usually with a solute, by hydrostatic pressure and requires a filtration membrane. Factors affecting rate are the amount of pressure and the size of pores in the filter. The substances needed for movement across blood vessels are water and small ions.
- Carrier-mediated Transport:
- Facilitated diffusion involves carrier molecules that passively transport solutes down a concentration gradient. Factors that affect rate are the amount of pressure, the size of pores in the filter, and the availability of carrier protein. The substances involved for all cells are glucose and amino acids.
- Active transport involves carrier molecules that actively transport solutes regardless of any concentration gradients. Factors that affect rate are the availability of carrier proteins, a substrate, and ATP. Substances needed to accomplish this for all cells are Na+, K+, Ca2+, Mg2+, plus other solutes by specialized cells.
- Vesicular Transport:
- Endocytosis involves the creation of vesicles containing fluid or solid material. Factors that affect the rate are various stimulus and mechanics as well as ATP. The substances involved for all cells are fluids and nutrients; for specialized cells, debris and pathogens.
- Exocytosis involves the fusion of vesicles containing fluids and/or solids with the cell membrane. Factors that affect rate are various stimulus and mechanics as well as ATP. Substances involved for all cells are fluids and debris.
