Exchange in Plants

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  • Created by: Nisha~
  • Created on: 29-10-13 16:12
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  • Exchange in plants
    • Gas exchange in plants
      • Plants need water for photosynthesis to take place
      • Carbon dioxide is taken into the leaf through diffusion
      • Adaptations
        • Flattened shape increases surface area for diffusion
        • Thin leaf means the distance the CO2 has to diffuse to the leafis short
        • The many air spaces allow CO2 to come into contact with many cells and give a large surface area for diffusion
      • However leaves constantly lose water through evaporation
        • If CO2 could diffuse so freely then so could water and then the plant would die
      • When it is dark the leaf does not need the CO2 for photosynthesis
      • Light is a limiting factor for photosynthesis in which case CO2 from respiration is used
        • However on warm sunny days lots of CO2 comes into the leaf by diffusion
      • More plant adaptations
        • Waxy cuticle which is waterproof and gasproof only allows water when needed
        • The leaf surface is covered in small openings know as stomata
          • These open to allow gases in and out
      • Carbon dioxide diffuses into air spaces along a concentration gradient
        • At the same time oxygen from cells is released into the air
          • Guard cell control the opening and closing of the stomata
            • However water can be lost from the leaves at the same time
    • Uptake of water and mineral ions in plants
      • Plant roots are adapted to absorb water and minerals from the soil
      • The roots are thin divided tubes with a large surface area
      • The cells on the outside have tiny projections which push out between soil particles
      • Water moves into the root hair cells by osmosis across the partially permeable cell membrane
      • Then there is only a short distance for it to move to the xylem
      • Plant roots also have mitochondria to supply energy
      • They also have the advantages of a  large SA and short pathways for water

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