Maintaining a Constant Internal Environment

1. 1 State [1 mark]

   State what is meant by homeostasis.

   Show answerHide answer

   Model answer

   The regulation of the conditions inside the body so that they stay constant.

   Mark scheme

   • Regulation of internal conditions to keep them constant — 1 mark
2. 2 Name [2 marks]

   Name two conditions in the body that are controlled by homeostasis.

   Show answerHide answer

   Model answer

   Body temperature and blood glucose concentration.

   Mark scheme

   • Body temperature — 1 mark
   • Blood glucose concentration, or water content — 1 mark
3. 3 Describe [3 marks]

   Describe the roles of the receptor, the coordination centre and the effector in a control system.

   Show answerHide answer

   Model answer

   The receptor detects a change in a condition. The coordination centre receives the information and decides what the response should be. The effector, which is a muscle or a gland, carries out the response.

   Mark scheme

   • Receptor detects the change — 1 mark
   • Coordination centre receives information and decides — 1 mark
   • Effector carries out the response — 1 mark
4. 4 Explain [3 marks]

   Explain why it is important that the body temperature stays close to 37 °C.

   Show answerHide answer

   Model answer

   The enzymes in the body have an optimum temperature of about 37 °C. If the temperature changes, the enzymes work more slowly, or they stop working. So the chemical reactions in the cells would be too slow, and the cells could not carry out their functions.

   Mark scheme

   • Enzymes work best at about 37 °C — 1 mark
   • A change slows or stops the enzymes — 1 mark
   • Reactions in the cells are affected — 1 mark
5. 5 Explain [3 marks]

   Explain what is meant by negative feedback, using the control of blood glucose as an example.

   Show answerHide answer

   Model answer

   Negative feedback is a response that reverses a change. When the glucose concentration of the blood rises, insulin is released, which makes the concentration fall back to normal. Once it is normal, less insulin is released.

   Mark scheme

   • A response reverses the change — 1 mark
   • Glucose rises, so insulin is released — 1 mark
   • The concentration falls, so less insulin is released — 1 mark
6. 6 Evaluate [6 marks]

   A runner takes part in a race on a hot day. Describe the changes that take place in the body of the runner, and explain how homeostasis helps the runner to stay healthy.

   Show answerHide answer

   Model answer

   The runner's muscles release heat, so the body temperature tends to rise, which is a stimulus. The muscles also use glucose and the runner loses water in sweat, so the glucose concentration and the water content of the body tend to fall. Receptors detect each of these changes, and a coordination centre, such as the brain or the pancreas, decides on the response. The effectors, which are glands and muscles, carry out the responses. For example, the sweat glands release more sweat, to cool the body, and glucose is released from stores to replace what is used. Each response reverses the change, which is negative feedback. This keeps the temperature close to 37 °C, so that the enzymes in the cells keep working, and keeps the glucose and water content steady, so that the cells have energy and do not gain or lose too much water.

   Mark scheme

   • Temperature rises, which is a stimulus — 1 mark
   • Glucose and water fall — 1 mark
   • Receptors detect the changes — 1 mark
   • Effectors respond, for example more sweating — 1 mark
   • Negative feedback reverses the change — 1 mark
   • Enzymes and cells keep working — 1 mark

Quick check

1. 1

   What is homeostasis?

   1. AGrowth of the body
   2. BRegulation of internal conditions so they stay constant
   3. CRelease of energy in respiration
   4. DMovement of water by osmosis
   Show answerHide answer

   B: Regulation of internal conditions so they stay constant

   The regulation of conditions inside the body to keep them constant.

2. 2

   What is the normal body temperature?

   1. A20 °C
   2. B30 °C
   3. C37 °C
   4. D45 °C
   Show answerHide answer

   C: 37 °C

   About 37 °C.

3. 3

   Which part of a control system carries out the response?

   1. AThe receptor
   2. BThe stimulus
   3. CThe coordination centre
   4. DThe effector
   Show answerHide answer

   D: The effector

   The effector.

4. 4

   Which of these is an effector?

   1. AA muscle
   2. BA temperature receptor
   3. CThe brain
   4. DA neurone
   Show answerHide answer

   A: A muscle

   A gland or a muscle carries out a response.

5. 5

   What does negative feedback do?

   1. AIt makes a change bigger
   2. BIt stops the receptors working
   3. CIt reverses a change
   4. DIt makes a condition fluctuate wildly
   Show answerHide answer

   C: It reverses a change

   It reverses a change and returns the condition to normal.

6. 6

   Why must the temperature of the body stay constant?

   1. AThe enzymes work best at about 37 °C
   2. BBones only grow at 37 °C
   3. CBlood stops flowing otherwise
   4. DOxygen is made at 37 °C
   Show answerHide answer

   A: The enzymes work best at about 37 °C

   The enzymes work best at about 37 °C.

7. 7

   Which of these is an internal change that the body responds to?

   1. AA cold day
   2. BEating a meal
   3. CA hot day
   4. DRain
   Show answerHide answer

   B: Eating a meal

   Eating a meal raises the blood glucose concentration.

8. 8

   Which of these is NOT usually kept constant by the body?

   1. ABody temperature
   2. BBlood glucose
   3. CWater content
   4. DThe amount of exercise
   Show answerHide answer

   D: The amount of exercise

   The body does not keep the amount of exercise constant.

9. 9

   How does hormonal control compare with nervous control?

   1. AIt is faster and shorter
   2. BIt is slower and lasts longer
   3. CIt uses no chemicals
   4. DIt only works on muscles
   Show answerHide answer

   B: It is slower and lasts longer

   It is slower, and the effects usually last longer.