Principles of homeostasis and negative feedback

Homeostasis

Involves physiological control systems that maintain the internal environment within restricted limits

Give 3 examples of what homeostasis controls

• Core temperature

• Blood pH

• Blood glucose levels

Outline the consequences of core temperature being too high (8 points)

1. Greater kinetic energy

2. Breaks hydrogen and ionic bonds that hold enzymes tertiary structure in place

3. Loss of tertiary structure

4. Active site changes shape

5. No longer complimentary to the substrate

6. Enzyme-substrate complexes cannot form

7. Activation energy cannot be lowered/chemical reactions not catalysed

8. Slower rate of reaction

Outline the consequences of core temperature being too low (4 points)

1. Less kinetic energy

2. Frequency of collisions between enzyme's active site and substrate decrease

3. Fewer enzyme substrate complexes form

4. Lower rate of reaction

Outline the consequences of pH being too high (8 points)

1. More OH^- ions released

2. Hydrogen and ionic bonds which hold enzymes tertiary structure in place are broken

3. Loss of tertiary structure

4. Active site changes shape and is no longer complementary to substrate

5. Enzyme substrate complexes cannot form

6. Activation energy cannot be lowered

7. Chemical reactions not catalysed

8. Slower rate of reaction

Outline the consequences of pH being too low (8 points)

1. More H⁺ ions released

2. Hydrogen and ionic bonds which hold enzymes tertiary structure in place are broken

3. Loss of tertiary structure

4. Active site changes shape and is no longer complementary to substrate

5. Enzyme substrate complexes cannot form

6. Activation energy cannot be lowered

7. Chemical reactions not catalysed

8. Slower rate of reaction

Outline the consequences of blood glucose being too high (8 points)

1. High levels of glucose in the blood lower the water potential

2. Water from the cells moves down the water potential gradient by osmosis into the blood

3. High blood pressure

4. Dehydration of cells

5. Lower rates of chemical reactions (as water is a metabolite a medium for chemical reactions)

Outline the consequences of blood glucose being too low (6 points)

1. Water moves into cells from blood down water potential gradient via osmosis

2. Cells swell

3. Less respiratory substrate for respiration

4. Lower rate of respiration

5. Less energy released

6. Less ATP produced

Purpose of negative feedback

Restores systems to their original level

Briefly outline the cycle of negative feedback

1. Stimulus (change in the internal environment)

2. Detected by receptor

3. Coordinator coordinates a negative feedback mechanism

4. Nerve impulses or hormones sent out

5. Reversal of the change

Give 2 examples of what negative feedback can be used to control

• Thermoregulation

• Blood glucose concentration

Positive feedback

Effectors respond to further increase the level away from the normal Level

Give 3 examples of what positive feedback can be used to control

• Prolactin in lactation

• Influx of sodium ions in inaction potential

• Blood clotting