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  • Created by: danni :)
  • Created on: 27-12-12 20:46
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  • homeostasis
    • positive feedback: does NOT play a part in homeostasis as it moves parameter away from norm.
      • e.g., if a person breaths in highly carbonated air, CO2 receptors register this and breathin rate increases causes even more CO2 to be breathed in.
    • negative feedback e.g., core body temp. receptor detects if the temp is within a suitable range, if not, communicates with effector that causes an action to return temp to normal
      • temp involves nervous and hormonal systems--> short time delay between detection, communication and action, results in oscillation around a set value.
        • nervous system= short term, rapid changes.
        • hormonal system=  slow but more long term changes
    • factors affecting the activities of a cell
      • Temperature:  low temp= metabolic reactions slow down; high temp= proteins denature & damage enzymes + cell mbs
      • amount of water: lack of water in tissue fluid --> water moves out of cell by osmosis--> metabolic reactions slow/ stop ; too much water in tissue fluid --> water moves into cell via osmosis --> cells swell/ burst
      • [glucose] : lack --> respiration slows/ halts= no energy ; too much in tissue fluid--> water moves out of cell  metabolic reactions slow/ stop
    • to control internal conditions to maintain a stable internal environment
    • temperature regulation
      • endotherms
        • temperature receptors: the hypothalamus continually monitors the temperature of the blood flowing through it. Peripheral receptors detect change in external temperature and provide a warning that the internal temperature might change
        • Can maintain their body temps.
        • advantages   1) fairly constant internal temp   2) activity possible when external temp is low   3)ability to inhabit cooler parts of the earth
        • disadvantages                                    1) significant part of energy intake used to maintain temp    2) More food required        3) less energy used for growth or more is needed to grow
      • ectotherms
        • Advantages     1) use less food for respiration      2) can survive longer without food                      3) can use more energy from food for growth
        • disadvantages                     1) less active during cooler times so at risk of predation.      2) may not be capable of activity during winter, meaning they need sufficient energy stores to last
        • relies on external sources to regulate its body temperature
      • water has a high latent heat of vaporisation which is why , when we sweat we cool down because the water evaporates, taking heat energy with it.
      • ectotherms (e.g., reptiles) cant control their temperature physiologically , so use behaviour mechanisms, such as laying in the sun to warm up, to control their body temperatures.


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