Reducing Water Loss

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  • Reducing Water Loss
    • Xerophytes
      • some plants are well adapted to living in very dry or arid conditions
      • Many Adaptations to reduce water loss from their leaves
        • densely packed spongy mesophyll reduces the cell surface area that is exposed to the air inside the leaves, less water will evaporate into theleaf air spaces
        • smaller leaves, particularly shaped like needles, reducing the total surface area of the leaves, so less water is lost
        • thicker waxy cuticle
        • hair on the surface of the leaves trap a layer of air close to the surface
          • this air can become saturated with moisture and will reduce the diffusion of water vapour out of the stomata (water potential vapour gradient reduced)
            • Pits with stomata at their base trap air too
        • Pits with stomata at their base trap air too
        • Rolling the leaves so the lower epidermis is not exposed to the atmosphere can trap saturated air
          • this air can become saturated with moisture and will reduce the diffusion of water vapour out of the stomata (water potential vapour gradient reduced)
          • some plants have a low water potential in their leaves, by maintaining high salt concentration in the cells
            • reduces the evaporation of water from the cell surfaces as the water potential gradient between the cells and the leaf air spaces is reduced
      • Marram Grass
        • specialises in living in sand dunes, where the water in the sand drains away quickly and may be salty, leaves may be exposed to very windy conditions
        • leaf rolled up  to trap air inside
        • hairs on lower surface reduce movement of air
        • thick waxy cuticle to reduce water evaporation from surface
        • trapped air in centre with high vapour potential
        • stomata in pits to trap air with moisture close to stomata
      • Unavoidable Loss
        • Plants exchange gases with their environments via stomata, so water can always be lost through them when they are open during the day
        • most plants can reduce losses by structural and behavioural adaptations
          • stomata are often found on the underneath of the leaf, not the top. Reducing Evaporation due to direct heating from the sun
          • a waxy cuticle on the leaf
          • most stomata are closed at night, when there is no light for photo-synthesis
          • deciduous plants lose their leaves during winter, when the ground may be frozen (less water available) or when temperatures may be too low for photo-synthesis

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