The cell needs various molecules and ions for its survival. At the same time, it needs to get rid of wastes produced inside it. How are this particles transforted in and out of the cell.
The plasma membrane that encloses the cell defines the boundary of the cell structure. More importantly, it is differentially permeable to allow only a certain molecules like water, small organic molecules, and some minerals, but not others, to pass through. Some small molecules also pass through the plasma membrane quickly; other have difficulty passing through and must be assisted across it. The plasma membrane consist of a lipid bilayer with with embedded proteins. It regulates the passage of the particles. How does passage of these particles happen? Through what processes do theg occura?
The transport molecules, ions and other particles across the plasma membrane occurs through passive or active transport.
Passive Transport
In passive transport molecules and other particles move to regions of lower concentration. The cell does not use energy in the process.
Diffusion
An example of passive transport is diffusion. The process by which particles spread through a liquid or, a gas medium. In diffusion, the net movement of particles is from a region of higher concentration to a region of lower concentration. In cells, water and alcohol easily diffuses accross the plasma membrane.
Facilitated Diffusion
Note that the plasma membrane contain proteins. The protein serves as carriers that allow some molecules and ions to pass through the plasma membrane into the cell. This process is called facilitated diffusion. Plasma membranes of red blood cells for example, utilize a protein carroer that transports only glucose into or out of the cell. Researches has discovered specific for an ion, sugar, salt and other substances. Facilitated diffusion is a form of passive transport.
Osmosis
Water is the most abundant compound in organism. It dissolves substances and transport them to different parts of the body. Water is also the medium where chemical reactions take place. Thus, water is extremely important to the life of organisms and cells.
However the amount of water in the cells is always kept at a constant level. Water must be able to get into the cells. How does water get into and out of the cells?
Osmosis is another form of passive transport wherein water diffuses or moves through a differentially permeable membrane. In osmosis, water moves from a region of high concentration to a region of a low concentration of water molecules. Water becomes available to organisms and cells through osmosis.