Cells and control fact sheet Microscopes Total magnification = eyepiece magnification x objective lens magnification Cell structure Mitosis Enzymes Enzymes are protein molecules that speed up chemical reactions in the cells of living things. (They are known as biological catalysts). There are thousands of enzymes in every cell. The chemical that an enzyme works on is called the substrate. The substrate fits into part of the enzyme called the active site like a ‘lock and key’. Each enzyme is specific to one substrate (each enzyme only works on one type of substrate). At low temperatures enzyme reactions slow down because substrate molecules move around more slowly and collide with enzyme molecules less frequently. At high temperatures the shape of active site enzyme is permanently changed (they are denatured) and they no longer work (the ‘key’ no longer fits the ‘lock’). The ideal or optimum temperature for human enzymes to work efficiently is 370c. Each enzyme has an optimum pH. High or low pH can also denature enzymes. Diffusion Diffusion is the movement of a substance from an area where it is concentrated to an area where it is less concentrated. This happens because of the passive, random movement of particles. Oxygen and glucose diffuse into our cells for respiration, carbon dioxide diffuses out of them. Carbon dioxide and oxygen diffuse in and out of leaves during photosynthesis. Active transport Active transport is the use of energy from respiration to move some substances across cell membranes against the direction in which they would normally diffuse. Osmosis Osmosis is the overall movement of water particles through a partially permeable membrane (cell membrane) from a dilute solution to a concentrated solution. These arrows show the net (overall) movement of water particles by osmosis: Concentrated Weak Weak Concentrated Equally Concentrated
