5.1 Homeostasis and control systems
7 exam questions worth 18 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which of these is an effector?
Choose one answer.
Correct Not quite: the answer is A sweat gland
Mark scheme
B (a sweat gland)
Model answer
B: a sweat gland. Effectors are muscles or glands.
Define the term homeostasis.
Mark scheme
- regulation / control of the internal conditions (of a cell or organism) (1)
- to maintain optimum conditions for function / for enzyme action (1)
- allow: in response to internal and external changes as an alternative to the second mark if 'optimum' is not given
Model answer
Homeostasis is the regulation of the internal conditions of a cell or organism to keep them at the optimum level for enzymes and cells to function, in response to internal and external changes.
Give three conditions inside the human body that are controlled by homeostasis.
Mark scheme
Any three from:
- blood glucose (sugar) concentration (1)
- body temperature (1)
- water level / water content of the blood (1)
- allow: ion concentration, pH, blood carbon dioxide concentration, metabolic rate / thyroxine level
Model answer
Blood glucose concentration, body temperature and the water level of the body.
All control systems include receptors, coordination centres and effectors.
Describe the job of each.
Mark scheme
- receptors detect stimuli / changes in the environment (1)
- coordination centres receive and process information (from receptors) (1)
- effectors (muscles or glands) bring about a response (that restores optimum levels) (1)
Model answer
Receptors are cells that detect a stimulus, a change in the environment. The coordination centre, such as the brain or pancreas, receives information from the receptors and processes it. Effectors are muscles or glands that carry out the response that brings conditions back to the optimum.
Explain why it is important that human body temperature is kept close to 37 °C.
Mark scheme
- (37 °C is the) optimum temperature for enzymes (1)
- if too hot, enzymes are denatured / active site changes shape (1)
- so the substrate no longer fits the active site / reactions stop (1)
- if too cold, reactions are too slow (1)
- (because) molecules have less kinetic energy / fewer collisions (1)
- so cells cannot carry out metabolism / respiration fast enough (1)
Max 4
Model answer
Enzymes in the body work best at their optimum temperature of about 37 °C. If the temperature rises too far, the shape of the active site changes and the enzyme is denatured, so the substrate no longer fits and the reaction stops. If the temperature falls too far, molecules have less kinetic energy and collide less often, so reactions such as respiration become too slow for the cells to function.
Explain what is meant by negative feedback.
Mark scheme
- a change from the normal / optimum level is detected (1)
- (and) causes a response that reverses the change / returns the level to normal (1)
Model answer
When a level changes from its normal value, the change is detected and triggers a response that reverses the change, returning the level to normal.
A person's blood plasma becomes much more dilute than normal.
Explain what happens to their red blood cells.
Mark scheme
- water moves into the cells (1)
- by osmosis (1)
- (because) the plasma is more dilute than the cytoplasm / water moves from dilute to concentrated solution (through a partially permeable membrane) (1)
- cells swell / may burst (1)
Max 3
Model answer
The plasma is now more dilute than the cytoplasm of the red blood cells, so water moves into the cells by osmosis through the partially permeable cell membrane. The cells swell and may burst.
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