1. Principles of Homeostasis
12.1

2. Learning Objectives Define homeostasis
Explain the importance of homeostasis
Describe how control mechanisms work
Explain how control mechanisms are co-ordinated
Success Criteria
You can define homeostasis and suggest what things need to be maintained in the body
You can create a mind map of ideas for why homeostasis is important
You can take notes on control mechanisms
You can answer an exam question on homeostasis

3. Starter What is homeostasis?
The maintenance of a constant internal environment
What things need to be maintained?
Temperature
Oxygen levels
Water levels
Tissue Fluid
Composition of blood

4. Why is homeostasis important?
Independence: Stops organisms being reliant on the external environment (wider choices of where to live etc.)
Enzymes: sensitive to pH and temperature changes. Big changes could cause denaturation and stop reactions occurring.
Why is homeostasis important?
Blood glucose: essential to maintain this to maintain water potential and also give cells a constant supply of glucose for respiration.
Water Potential: changing this in blood/tissue fluid could make cells shrink or even burst. Would prevent cells operating normally.

5. Control Mechanisms Stages of Homeostatic Control
The Set Point (the norm)
Receptor (detects variations)
Controller (co-ordinates info and sends instructions)
Effector (brings about changes)
Feedback Loop (tells receptor about the changes)

6. Control Mechanisms Receptors Detect the change Control Centre
Coordination
Effector
Have an effect on the system
Output
Rise in some parameter
Input
Fall in some parameter

7. Analysing Info from Receptors
Changes can be detected by a number of different receptors
This gives the brain a better picture of what is being altered
Allows a more informed response to be made

8. Plenary – Exam Q
How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency? (5)

9. Plenary – Exam Q ANSWERS
1. Body temp./37°C is optimum temp for enzymes; 2. excess heat denatures enzymes/alters tertiary structure/alters shape of active site/enzyme; 3. substrate cannot bind/eq,; 4. reactions cease/slowed; 5. too little reduces kinetic energy of molecules / molecules move more slowly; 6. fewer collisions/fewer ES complexes formed’ max 5

10. Learning Objectives Define homeostasis
Explain the importance of homeostasis
Describe how control mechanisms work
Explain how control mechanisms are co-ordinated
Success Criteria
You can define homeostasis and suggest what things need to be maintained in the body
You can create a mind map of ideas for why homeostasis is important
You can take notes on control mechanisms
You can answer an exam question on homeostasis