what is difference between diffusion and facilitated diffusion?
• It is the movement of particles of a substance from a region of its higher concentration to the region of its lower concentration until the molecules are evenly distributed throughout the available space.
• No energy expenditure takes place.
• In diffusion, molecules move in a random fashion, the net result being substances moving from regions of higher concentration to regions of lower concentration.
• It is a slow process and is not dependent on a living system.
• Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, temperature and pressure.
• It is an important factor in the supply of carbon dioxide for photosynthesis and the loss of water vapour from the leaves during transpiration.
• Substances that have a hydrophilic moiety, find it difficult to pass through the membrane. Membrane proteins provide sites at which such molecules cross the membrane. They do not setup a concentration gradient. A concentration gradient must already be present for molecules to diffuse even if facilitated by the proteins. This process is called facilitated diffusion.
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• In facilitated diffusion special proteins help move substances from a low to a high concentration this would require input of energy.
• Facilitated diffusion is very specific. It allows cell to select substances for uptake. It is sensitive to inhibitors which react with protein side chains.
• The proteins form channels in the membrane for molecules to pass through. Some channels are always open, other can be controlled. Some are large, allowing a variety of molecules to cross.
• The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules upto the size of small proteins to pass through e.g. water channels are made up of eight different types of