exchange of materials (in plants and gut)

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  • exchange of materials in plants + gut
    • exchange in plants
      • stomata in plants allow CO2 to diffuse into leaf from atmosphere
      • underneath of leaf- exchange surface- many stomata
      • leaves= flat= increase surface area, gas exchange more effective. thin= less distance to diffuse
      • walls of cells- exchange surface, Air sacks increase surface area, more chance for CO2 to get in cell
      • O2 + water vapour lost through stomata (water vapour lost= evaporation)
      • size of stomata controlled by guard cells, Close stomata if plant losing water faster than can replace. Plant wilt without
      • water evaporates from cells inside leaf. Escapes by diffusion because a lot inside leaf, less in air. Faster when hot, dry, windy
      • water + mineral ions absorbed by plant in roots.
      • root hair cells increase surface area of roots= faster absorbsion
    • transpiration
      • caused by evaporation + diffusion from stomata in leaves
      • creates shortage of water in leaf. More drawn up through xylem to replace.
      • means more drawn up from roots, so constant transpiration stream (movment of water through plant)
      • transpiration= side effect of way leaves adapted for photosynthesis. Have stomata so easy gas exchange. more water on inside of plant than outside in air. water escapes through stomata.
      • plant could dehydrate if rate of evaporation greater than water uptake by roots.
      • guard cells close= prevent excess water loss. wilting of whole plant= prevent excess water loss. leaves collapse+ hang down= smaller surface area.
    • exchange in gut
      • food digested= small, soluble molecules. in small intestine solutes absorbed by blood
      • villi line inner surface of small intestine- exchange surface for food molecules.
        • Villi are efficient exchange surfaces foe aborption of soluble products of digestion by diffusion or active transport.
      • villi- increase surface area so digested food is absorbed more quickly in blood.
        • thin walls and many capillaries close to wall, good blood supply assists absorption
          • soluble products absorbed by active transport/ digestion

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