Diffusion is the process by which molecules spread from areas of high concentration, to areas of low concentration. This happens without any outside force as it is a spontaneous process. The process is a result of the intrinsic thermal energy (heat) found in all molecules at temperatures above absolute zero. When the molecules become uniform throughout a space it is called equilibrium (Biologycorner.com, 2015).
There is also passive transport, this is diffusion over a cell membrane. This is also a spontaneous diffusion where molecules move from a concentrated area, to a less concentrated area. Due to the cell membrane only allowing certain molecules through, there will be different rates of diffusion for different molecules. Some molecules may need help to cross the cell membrane, this is called facilitated diffusion.
Osmosis is the diffusion of water across the semipermeable membrane, from an area of low solute concentration (hypotonic solution), to an area of high solute concentration (hypertonic solution). Hypotonic is when the solution outside of the red blood cells has a lower osmotic pressure than the cytoplasm of the red blood cells. The cells take in water in an attempt to equalize the osmotic pressure, causing them to swell and potentially burst (Biologycorner.com, 2015). Hypertonic is when the osmotic pressure of the solution outside the blood cells is higher than the osmotic pressure inside the red blood cells. The water inside the blood cells then exit the cell in an attempt to lower the pressure, causing the cell to then shrink. Isotonic solution is when the osmotic pressure is the same inside and outside of the cell. This means the cells are normal. This is a spontaneous process where a substance moves from the less concentrated area, to the more concentrated area. The direction of water flow is determined by the solute concentration and not by the nature of the solute molecules themselves(Bailey,2015).
Active transport is the movement of a substance across the membrane, from a lower concentration to a higher concentration by using energy. This goes against a concentration gradient and the usual form on energy used is ATP. Carrier proteins that are found in the cells membrane, use energy to transport molecules or ions across the membrane. Active transport is used when the concentration of a cell is higher than the outside of the cell or, when a molecule is too large to diffuse through the membrane.
Phagocytosis is the process of where a cell ingests foreign bodies and cell debris, such as, bacteria, parasites and dead host cells. It does this by hunting out the debris, stretching itself around it and then engulfing it. This is how vesicles are formed, vesicles are small sacks within a cell containing fluid.
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Essay Sauce, How materials are exchanged across the cells membrane. Available from:<http://www.essaysauce.com/education-essays/how-materials-are-exchanged-across-the-cells-membrane/> [Accessed 22-01-19].