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| Pregunta | Respuesta |
| Active transport. Active transport is the movement of particles against a concentration gradient, from an area of low concentration to and area of high concentration, using energy released by respiration. |
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| Active transport is the opposite of diffusion. Like Diffusion and Osmosis, Active transport is the movement of particles in and out of cells. | In the digestive system, Active transport moves molecules from low concentrations of nutrients in the gut to high concentrations of nutrients in the blood, it is what stops us starving. |
| When there is high concentration of nutrients in the gut, the molecules diffuse naturally into the blood. When there is lower concentration of nutrients in the gut than the blood, then active transport is needed to move particles in and out of cells. This process uses energy from respiration. | |
| Factors Affecting substance movement: Surface area to volume ratio, Temperature, Concentration Gradient. | |
| Surface area to volume ratio. The rate of diffusion, osmosis and active transport is higher in cells that have a larger surface area to volume ratio. | |
| A 2 cm2 cube cell will have: Area 2x2x6 (faces) = 24cm2 Volume 2x2x2 = 8cm3 Ratio 24:8 = 3:1 | A 3 cm2 cube cell will have: Area 3x3x6 (faces) = 54 cm2 Volume 3x3x3 = 27 cm3 Ratio 54:27 = 2:1 |
| In the example movement in and out of the cell will be faster, as there is a higher surface area to volume ratio | Temperature. As particles warm up, they have more energy, if they have more energy, they move faster. this means temperature increases the movement in and out of cell. |
| Concentration Gradient. Substances move faster in and out of cells if there is a big difference in concentration gradient. When there are a lot more particles on one side, there are more to move across. | This factor only affects diffusion and osmosis, concentration gradient doesn't affect Active transport. |
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