3.6.4.1 - Principles of homeostasis and negative feedback

Question 1

Describe homeostasis in mammals

Answer 1

● Maintenance of a stable internal environment within restricted limits
● By physiological control systems

Question 2

Examples of internal environments in a mammal that are controlled by homeostasis

Answer 2

core temperature, blood pH, blood glucose concentration, blood water potential

Question 3

Explain the importance of maintaining stable core temperature

Answer 3

● If temperature is too high:
○ Hydrogen bonds in tertiary structure of enzymes break
○ Enzymes denature; active sites change shape and substrates can’t bind
○ So fewer enzyme-substrate complexes

● If temperature is too low:
○ Not enough kinetic energy so fewer enzyme-substrate complexes

> important enzyme-controlled (metabollic) reactions can’t take place at sufficient/optimum rate

Question 4

Explain the importance of maintaining stable blood pH

Answer 4

● Above or below optimal pH, ionic / hydrogen bonds in tertiary structure break
● Enzymes denature; active sites change shape and substrates can’t bind
● So fewer enzyme substrate complexes
> important enzyme-controlled (metabollic) reactions can’t take place at sufficient/optimum rate

Question 5

Explain the importance of maintaining stable blood glucose concentration

Answer 5

Too low (hypoglycaemia)
● Not enough glucose (respiratory substrate) for
respiration
● So less ATP produced
● Active transport etc. can’t happen → cell death

Too high (hyperglycaemia)
● Water potential of blood decreases
● Water lost from tissue to blood via osmosis
● Kidneys can’t absorb all glucose → more water
lost in urine causing dehydration

Question 6

Describe the role of negative feedback in homeostasis

Answer 6

1. Receptors detect change from optimum
2. Effectors respond to counteract change
3. Returning levels to optimum / normal

Question 7

Example of negative feedback

Answer 7

control of blood glucose
concentration, blood pH, core temperature and blood water potential

Question 8

Explain the importance of conditions being controlled by separate
mechanisms involving negative feedback

Answer 8

● Departures in different directions from the original state can all be controlled / reversed
● Giving a greater degree of control (over changes in internal environment)

Question 9

Describe positive feedback

Answer 9

1. Receptors detect change from normal
2. Effectors respond to amplify change
3. Producing a greater deviation from normal

Question 10

Examples of positive feedback

Answer 10

onset of contractions
in childbirth, blood clotting