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Summary OCR A-Level Biology 5.1.2 Homeostasis
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Revision summary of key knowledge from OCR A-Level Biology 5.1.2 Homeostasis.
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HomeostasisHomeostasis – the maintenance of an organism’s internal environment within set limits
Conditions Controlled by Homeostasis
Temperature – enzymes require an optimum temperature to function properly
Blood Water Potential – too high affects its ability to carry oxygen, too low dehydrates
body cells
Blood Glucose Levels – affects water potential of blood
Blood Salt Concentration – affects water potential of blood
Blood pH – enzymes require an optimum pH to function properly
Carbon Dioxide Levels – acidic gas so affects blood pH
Blood Pressure – can cause stroke or fainting
Importance of Homeostasis
Enzyme activity – enzymes can only function within optimum conditions
Cell size – changes in water potential in blood can cause crenation or swelling of cells
Independence from external conditions allows the organism to maintain a constant
level of activity regardless of conditions
Feedback
Negative Feedback – mechanism to reverse or correct a change away from the optimum
Positive Feedback – mechanism to amplify or increase a change leading to further deviation
away from the optimum – rare since it tends to produce unstable conditions
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