B3 Biology Unit

689 Words3 Pages
B3.1 Movement of molecules in and out of cell Dissolved substances Dissolved substances move by diffusion and by active transport. Diffusion: The movement of particles in a liquid or gas from an area where they are in higher concentration to an area where they are in lower concentration. - The greater the difference in concentration, the faster the rate of diffusion. - 2 examples of diffusion through the cell membrane: o Oxygen required for respiration diffuses into cells. o Carbon dioxide produced by respiration diffuses out of cells. Osmosis: - Water often moves across boundaries by osmosis. - Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules. - Differences in the concentrations of the solutions inside and outside a cell cause water to move into or out of the cell by osmosis. - If there is a higher solute concentration on one side of a membrane, water will move in that direction. Sports Drinks -Most soft drinks contain water, sugar and ions. -Sports drinks contain sugars to replace the sugar used in energy release during the activity. -They also contain water and ions to replace the water and ions lost during sweating. - If water and ions are not replaced, the ion / water balance of the body is disturbed and the cells do not work as efficiently. Energy drinks - Contain the same concentration of ions as the body fluids, and a high concentration of glucose. - This enables rapid uptake of glucose. Rehydrating drinks - These contain lower concentration of ions than in body fluids. - This enables rapid uptake of water by osmosis. - These drinks enable people to become quickly rehydrated after exercise. Active Transport: - The process by which cells absorb substances against a concentration gradient. - The substances
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