15.2.1

Overview of Homeostasis

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Homeostasis

Homeostasis is the maintenance of the internal environment within an optimum range. Homeostasis is necessary to control the following factors:

High temperature

High temperature

  • Homeostasis maintains optimum core body temperature. This is approximately 37°C in humans.
  • If body temperature rises above the optimum range, enzymes denature.
  • The higher temperature causes the hydrogen bonds that maintain the enzyme structure to break.
  • This alters the enzyme active site so the enzyme can no longer catalyse reactions (e.g. respiration).
Low temperature

Low temperature

  • If temperature falls below the optimum range, enzyme activity declines.
  • Decreased enzyme activity causes the rate of important reactions (e.g. respiration) to slow down.
Blood pH

Blood pH

  • Homeostasis maintains blood pH.
  • If blood pH rises above (too alkaline) or falls below (too acidic) the optimum range, enzymes denature.
  • Denatured enzymes can no longer catalyse important reactions.
  • Optimum pH range is normally around pH 7. Some enzymes have very different optimum ranges (e.g. enzymes in the stomach have a very acidic optimum pH).
High blood glucose

High blood glucose

  • Homeostasis maintains blood glucose concentration.
  • If blood glucose levels rise above the optimum range, the water potential of the blood is reduced.
  • Low water potential in the blood causes water to diffuse out of the cells by osmosis and into the blood.
  • This makes the cells flaccid and they die.
Low blood glucose

Low blood glucose

  • Homeostasis maintains blood glucose concentration.
  • If blood glucose levels fall below the optimum range, there is not sufficient glucose for respiration.
  • Respiration rate declines and energy levels fall.

Negative Feedback

Negative feedback is the mechanism that restores systems to the original level. The steps involved in these mechanisms are:

1) Detect change

1) Detect change

  • Change in the internal environment (stimulus) is detected by receptors.
  • Receptors (e.g. thermoreceptors) are stimulated when the level is too high or too low (e.g. temperature).
2) Counteract change

2) Counteract change

  • Receptors send a signal to the effectors through the nervous system.
  • The effectors counteract the change (e.g by restoring body temperature to 37°C).
  • Negative feedback can only maintain the internal environment within a specific range. If a change is too dramatic, negative feedback may not be able to prevent it.

Multiple Negative Feedback Mechanisms

Multiple negative feedback mechanisms provide a greater degree of control of the internal environment.

More control

More control

  • Multiple feedback mechanisms provide more control because the body can respond to multiple changes away from the optimum.
    • E.g. Body temperature can be reduced or increased by multiple mechanisms.
Faster response

Faster response

  • Multiple feedback mechanisms also provide a faster response because the body can respond in more ways to a change away from the optimum.
    • E.g. If body temperature decreases, negative feedback can increase body temperature by both shivering and vasoconstriction.
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1

Unity & Diversity - Molecules

1.1

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Introduction to Cells

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Viruses

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Unity & Diversity - Organisms

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Unity & Diversity - Ecosystems

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Form & Function - Molecules

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Form & Function - Cells

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Gas Exchange

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Form & Function - Ecosystems

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9

Interaction & Interdependence - Molecules

9.1

Enzymes

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9.2

Metabolism

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9.3

Cell Respiration

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9.4

Photosynthesis

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10

Interaction & Interdependence - Cells

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Interaction & Interdependence - Organisms

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Integration of Body Systems

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Continuity & Change - Molecules

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DNA Replication

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Protein Synthesis

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Continuity & Change - Cells

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Water Potential

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15

Continuity & Change - Organisms

15.1

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15.2

Homeostasis

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16

Continuity & Change - Ecosystems

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Stability & Change

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Practice questions on Overview of Homeostasis

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    If our internal conditions are not regulated, which of the following could denature?Multiple choice
  2. 2
    Which of the following statements about homeostasis are true?True / false
  3. 3
    Which of these is NOT an example of homeostasis?Multiple choice
  4. 4
    Which of the following statements about negative feedback are true?True / false
  5. 5
    What is the optimum human body temperature?Multiple choice
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Grade 4-5 (Scientific Practices) - Inheritance

Blood Glucose Concentration