1. Topic 9: Control Systems
C/W /10/2016
Estimate: 12 x double lessons, mid topic test after 6 lessons
Multiple choice quiz after 6 lessons
End of topic test after 12 lessons

2. C/W /10/2016
Homeostasis
Know that homeostasis is the maintenance of a state of dynamic equilibrium
Understand the importance of maintaining pH, temperature and water potential in the body
Understand what is meant by negative feedback and positive feedback control

3. Key Definitions
Homeostasis – Maintenance of a state of dynamic equilibrium in the body, despite changes in the external or internal conditions
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4. What factors do we need to control in our body?pH
Temperature -Thermoregulation
Water potential
In your exercise books, say why it is important that these 3 variables are controlled.
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5. pH Keeps protein structures stable
Synoptic link – Topic 1 – Protein Structure – Primary, Secondary, Tertiary, Quateranry pH
Keeps protein structures stable
Enzymes can function at their optimum acitivity
Structure of cell membranes can remain stable.
Link with transport of Carbon Dioxide away from body cells.
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6. Core temperature Synoptic link – Enzyme structure and active site
Enzyme activity maintained at optimum levels to control cellular reactions
Maintains integrity of cell membranes to control movement in and out of cells.
37C
Water potential
Water potential of body fluids must remain within narrow limits to avoid osmotic effects that could damage or destroy the cells
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7. What does homeostasis involve?
Synoptic link – Enzyme structure and active site
What does homeostasis involve?
Changes in the body are detected by sensors, also called receptors. They send messages to effectors that either work to reverse the change or to change or to increase it in a number of different feedback systems. Effectors are usually muscles or glands.
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8. C/W /10/2016
Checkpoints
Know that homeostasis is the maintenance of a state of dynamic equilibrium
Understand the importance of maintaining pH, temperature and water potential in the body
Understand what is meant by negative feedback and positive feedback control

9. Feedback systems
Most feedback systems in mammals are negative feedback system. They provide a way of maintaining a condition such as a concentration of a substance, within a narrow range. A change in conditions is registered by receptors and as a result effectors are stimulated to restore the equilibrium.
Next…. Complete negative feedback activity.
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10. Using the card sort and template
Sort the negative feedback cards onto the correct template.
We will go through this as a class.
You should then draw out a neat version of this in your exercise books.
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11. Negative Feedback Systems
Norm
(normal level of a particular factor)
Negative Feedback Systems
Fall to a lower level
Rise to a higher level
Receptor
Detects change
Receptor
Detects change
Communication (1) by hormonses or (2) by nervous system via coordination centre
Communication (1) by hormonses or (2) by nervous system via coordination centre
Effector
Carries out response which brings about corrective change
Effector
Carries out response which brings about corrective change
Norm
(normal level of a particular factor)
Rise to normal level
Fall to normal level
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12. C/W /10/2016
Checkpoints
Know that homeostasis is the maintenance of a state of dynamic equilibrium
Understand the importance of maintaining pH, temperature and water potential in the body
Understand what is meant by negative feedback and positive feedback control

13. Definitions
Negative feedback – Provides a way of maintaining a condition within a narrow range. A change in condition is registered by receptors and as a result effectors are stimulated to restore the equilibrium.
Positive Feedback – Where effected work to increase an effect that has triggered a response.
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14. Positive Feedback
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15. Positive Feedback mechanisms
Baby pushes against cervix – cervix stretches
Stretch receptors in cervix send impulses to brain
Brain stimulates pituitary to release oxytocin
Oxytocin makes uterus contract harder pushing baby against cervix
No return to homeostasis. This causes contractions to become stronger and more frequent.
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16. C/W /10/2016
Checkpoints
Know that homeostasis is the maintenance of a state of dynamic equilibrium
Understand the importance of maintaining pH, temperature and water potential in the body
Understand what is meant by negative feedback and positive feedback control

17. Questions
What is homeostasis and why is it so important in living organisms?
In the past, homeostasis was described as the maintenance of a steady internal state. Why do you think this definition has changed?
Suggest why there are many negative feedback systems in mammals and relatively few positive feedback systems.
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18. Answers
What is homeostasis and why is it so important in living organisms?
In the past, homeostasis was described as the maintenance of a steady internal state. Why do you think this definition has changed?
Suggest why there are many negative feedback systems in mammals and relatively few positive feedback systems.
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19. Exam Questions
Complete the data analysis questions relating to Homeostasis. We will mark these in in class. You have 20 minutes to complete.
You will then put them in the Exam Practice section of your folder.
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20. Topic 1 recap…
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21. Topic 1 recap… ANSWERS
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23. This relates to the following specification point:
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