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diffusion
net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient until an equilibrium is reached
e.g. diffusion in amoeba: partially permeable cell membrane allows small molecules like oxygen and carbon dioxide to enter but not large molecules like protein
e.g. diffusion in lungs: blood passing through lungs have more carbon dioxide than oxygen
blood has lower concentration of oxygen than carbon dioxide so, net movement of oxygen molecules from higher conc in air space in lungs to lower conc in blood, down a conc gradient
net movement of carbon dioxide molecules from a region of higher conc in blood to lower conc in air spaces in lung, down a conc gradient
osmosis
net movement of water molecules from a region of higher water potential to a region of lower potential, down a concentration gradient, through a partially permeable membrane
osmosis in plant & animal cells
dilute solution: solution has a higher water potential than cell, net movement of water molecules from solution to cell down a water potential gradient, across a partially permeable membrane, plant cell will swell and become turgid but not burst due to cell wall being able to withstand turgor pressure but animal cell will lyse
concentrated solution: cell has a higher water potential than solution, net movement of water molecules from cell to solution down a water potential gradient, across a partially permeable membrane, plant cell will become plasmolysed while animal cell becomes crenated
isotonic solution: cell and solution has same water potential so no net movement of water molecules hence, no change in size and turgidity of cell
active transport
net movement of molecules from a region of lower concentration to a region of higher concentration against a concentration gradient
energy released via respiraton is needed for active transport to take place, hence only living things that respire undergoes active transport
factors that affect movement of molecules
travel distance - the shorter the travel distance between molecules, the higher the rate of movement of molecules
steepness of gradient - the steeper the gradient, the higher the rate of movement of molecules
surface area to volume ratio - the larger the surface area to volume ratio, the higher the rate of movement of molecules
temperature of particles - the higher the temperature, molecules gain kinetic energy and move faster