Biology B3 Revision tool

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    • Transpiration stream
      • Water evaporates from palisade cells
        • Water drawn from xylem cells in leaf to replace it
          • Water molecules stick together - pulls more from leaf
            • Sets of stream of replacement;
              • Water in xylem replaced by water from xylem tube
                • Water in xylem tube replaced from stem
                  • Water from stem replaced from roots
      • Against concentration gradient
        • Osmosis
    • Controlling body temperature
      • Temperature receptors in skin detect changes in external temp
        • Send information to hypothalamus
          • This area of brain has receptors for testing blood temp
            • Triggers effectos to keep body temp at 27 deg Celsius.
              • Effectors = sweat glands and muscles
              • If we are too hot, the processing center sends nerve impulses to sweat glands to produce sweat
                • Evaporation of sweat needs energy, cooling you
                  • If the air is humid, the sweat cannot evaporate as easily due to concentration difference of water being lower
                • Hairs lie flat to let heat escape
              • If too cold, vasoconstriction to bring blood into the body to keep it warm
                • Hair sticks up to trap heat against skin
    • Blood sugar control
      • Too high;
        • Insulin  secreted by pancreas into blood
          • Liver convers glucose into glycogen
            • Glycogen is stored - blood sugar goes down
      • Too low;
        • Insulin not secreted into blood

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