3.6.4.1 Principles of homeostasis and negative feedback

Question 1

What is homeostasis and why is it necessary?

Answer 1

• Homeostasis is the maintenance of the internal environment within restricted limits.
• It keeps your internal environment stable which is vital for cells to function properly.

Question 2

Why is it important to control blood pH?

Answer 2

Enzymes become denatured if blood pH is high or low.

Question 3

Why is it important to control blood glucose concentration?

Answer 3

• If blood glucose conc. is too high, the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis.
• This can cause the cells to shrivel up and die.
• If blood glucose conc. is too low, cells are unable to carry out normal activities…
• …because there isn’t enough for respiration to provide energy.

Question 4

A: “Hyperthermia happens when the brain can’t work properly and body temperature continues to increase.”
B: “When body temperature is low mechanisms return the temperature to normal.”
Which statement is describing a positive feedback mechanism?
Give a reason for your answer.
[1 mark]

Answer 4

• Statement A…

- …because body temperature continues to increase from the normal level and isn’t returned.

Question 5

Describe and explain what effect a very high body temperature has on metabolic reactions.
[2 marks]

Answer 5

• It makes metabolic reactions less efficient…

- …because the enzymes that control metabolic reactions may denature.

Question 6

Describe the importance of of multiple negative feedback mechanisms in homeostasis.
[2 marks]

Answer 6

• They give more control over changes in the internal environment than just having one feedback mechanism.
• This is because you can actively increase or decrease a level so it returns to normal.