Movement Essay

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IGCSE Biology 3 Movement in & out of cells To get into or out of cells, dissolved substances have to cross the cell membranes. solute ~ particles in solution ( e.g. glucose, sodium ions, chloride ions ). solvent ~ liquid in which the particles are dissolved ( e.g. water ). Solute and solvent molecules move around randomly. Solutes can move into and out of cells by diffusion and osmosis Define diffusion as the net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement. Diffusion Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allow this to happen. Diffusion occurs when particles move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. The greater the difference in concentration, the faster the rate of diffusion. [pic] Describe the importance of diffusion of gases and solutes and of water as a solvent. Examples of diffusion: |location |particles move |from |to | |intestine |digested food products |intestinal cavity |blood in capillary of villus | |lungs |oxygen |alveolar air space |blood circulating around the lungs | In the intestine, the concentration of molecules used by the body

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