Gas & Solute Exchange

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  • Created by: Christie
  • Created on: 30-04-13 10:11
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  • Gas & Solute Exchange
    • Osmosis
      • The movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration
        • A partially permeable membrane is one with very small holes in it, only tiny molecules (like water) can get through. The molecules can pass through both ways as they move about randomly and there is a net flow into the region with fewer water molecules to "even it up".
          • In cells
            • Tissue fluid surrounds cells in the body (water, oxygen, glucose, etc. dissolved) squeezed out of blood capillaries and has a different concentration to fluid inside a cell so keeps dilution or concentration correct through water transfer.
    • Diffusion
      • Particles move from an area of high concentration to an area of low concentration
        • This process can happen in gases or solutions, e.g. a smell spreading through a room, or dissolved particles diffusing in and out of cells through cell membranes
          • Diffusion in leave cells and their adapted structure
            • Carbon dioxide diffuses into air spaces in the leaf, then diffuses into cells where photosynthesis happens. Stomata (tiny holes) make an exchange surface on the underneath of the leaf for CO2 to diffuse into, and oxygen and water vapour to diffuse out of. Guard cells control the water lost by closing the stomata if the plant is losing water faster than replaced, to stop the plant wilting. Flattened shape of the leaf increases area of the exchange surface so it is more effective. Walls of the cells form another exchange surface and air spaces inside the leaf increase this area for more chance of CO2 to get in cells.
              • REMEMBER: water vapour evaporates from cells inside leaf, then  escapes by diffusion as more inside leaf than in air outside. Evaporation is quickest in HOT, DRY, WINDY conditions
          • Diffusion through Cell Membranes
            • Gas Exchange happens in the LUNGS. Their job is to transfer oxygen to the blood and remove waste carbondioxide from it. They contain millions of little air sacs called alveoli for this gas exchange to take place. Alveoli are specialised to maximise diffusion, having ENORMOUS SURFACE AREA (about 75m2 in humans), MOIST LINING for dissolving gases, THIN WALLS and a good BLOOD SUPPLY.
            • The inside of the small intestine is covered in millions of VILLI, which provide a really big surface area so that digested food is absorbed more quickly into the blood. They have a SINGLE LAYER of SURFACE CELLSand a GOOD BLOOD SUPPLY to assist quick absorbtion.
              • Digested food ALSO moves by ACTIVE TRANSPORT
    • Active Transport
      • This is when substances need to be absorbed against a concentration gradient, i.e from a lower to a higher concentration
        • Active transport requiresENERGY from respiration to make it work
          • Active Transport in the Gut
            • Sometimes there is a low concentration of nutrients in the gut, but a high concentraion in the blood, active transport is used, rather than the amino acids and glucose diffusing into the blood
          • Active Transport in Root Hairs
            • Root hairs are specialised as the cells on the surface of the plant roots grow into long 'hairs' which stick out into the soil, giving a big surface area for absorbing water and mineral ions. The concentration of minerals is usualy higher in the root hair cell than the soil, so active transport allows the plant to absorb minerals from a dilute solution, against a concentration gradient, using energy.
          • "Imagine a pen of sheep in a field- if you open the pen the sheep will happily DIFFUSE from the area of high sheep concentration into the field, which has a low sheep concentration, you won't have to do a thing. To get them back in the pen though, you'd have to use quite a bit of ENERGY."
  • This process can happen in gases or solutions, e.g. a smell spreading through a room, or dissolved particles diffusing in and out of cells through cell membranes
    • Diffusion in leave cells and their adapted structure
      • Carbon dioxide diffuses into air spaces in the leaf, then diffuses into cells where photosynthesis happens. Stomata (tiny holes) make an exchange surface on the underneath of the leaf for CO2 to diffuse into, and oxygen and water vapour to diffuse out of. Guard cells control the water lost by closing the stomata if the plant is losing water faster than replaced, to stop the plant wilting. Flattened shape of the leaf increases area of the exchange surface so it is more effective. Walls of the cells form another exchange surface and air spaces inside the leaf increase this area for more chance of CO2 to get in cells.
        • REMEMBER: water vapour evaporates from cells inside leaf, then  escapes by diffusion as more inside leaf than in air outside. Evaporation is quickest in HOT, DRY, WINDY conditions
    • Diffusion through Cell Membranes
      • Gas Exchange happens in the LUNGS. Their job is to transfer oxygen to the blood and remove waste carbondioxide from it. They contain millions of little air sacs called alveoli for this gas exchange to take place. Alveoli are specialised to maximise diffusion, having ENORMOUS SURFACE AREA (about 75m2 in humans), MOIST LINING for dissolving gases, THIN WALLS and a good BLOOD SUPPLY.
      • The inside of the small intestine is covered in millions of VILLI, which provide a really big surface area so that digested food is absorbed more quickly into the blood. They have a SINGLE LAYER of SURFACE CELLSand a GOOD BLOOD SUPPLY to assist quick absorbtion.
        • Digested food ALSO moves by ACTIVE TRANSPORT

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