GCSE OCR 21st Century Biology B4


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  • Created by: Marjack
  • Created on: 18-06-11 18:35


Homeostasis- keeping a constant internal environment:

Water Content- balancing inputs (Food, Drink, Respiration)

and outputs (Breathing, Sweating, Urine and Faeces)

Body Temperature- must be kept at around 37 (deg. celsius)

-if it's too hot your body gets rid of heat using various methods

-if it's too cold your body maintains and raises heat using various methods.

However all methods are run by Negative Feedback.

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Exercise and Climate

Strenuous Exercise and Extreme Climates can affect Homeostasis:

Strenuous Exercise changes:

  • Temp- exercising generates heat so your temp increases
  • Water Content- during exercise you gain heat so lose water to sweat and water vapour is lost as your breathing rate increases.

Extreme Climates changes:

  • Hot Climates- same affect as strenuous exercise
  • Cold Climates- body temp to decrease rapidly
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Negative Feedback

Neg. Feedback helps keep internal environment constant.

If water or temperature levels get TOO high or TOO low, your body uses negative feedback to bring it back to NORMAL. (Homeostasis)

All Homeostatic control systems, like neg. feedback, use three main components:

  • Receptor- detects STIMULUS (levels too high/low)
  • Processing Centre- receives INFO and coordinates a RESPONSE
  • Effectors-produce response which counteracts a change (levels decrease/increase).

This process of Negative Feedback is automatic, you don't have to think about it.

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Antagonistic Effectors

Some effectors (produce response once they are triggered by processing centre) work antagonistically.

E.g. one effector heats and another cools- they'll work at the same time to achieve a very precise temperature. This mechanism allow a MORE sensitive Response.

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leah murray


These are good so far but have you finished them?

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