7.5.1 Negative and positive feedback and homeostasis during exercise Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

The 20 questions

1. What is the defining feature of negative feedback control?

   • The response reduces the change that triggered it, returning the system towards its set point over time
   • The response occurs only after the stimulus has been removed, so the variable is not corrected in time
   • The response has no effect on the original stimulus, but it is triggered by the same change each time
   • The response increases the change that triggered it, so the system moves further away from its starting value

2. What is the defining feature of positive feedback control?

   • The response amplifies the original change, pushing the system further from its starting point until a limit is reached
   • The response keeps the variable at a fixed set point regardless of how strong the original stimulus becomes
   • The response is always slower than the stimulus, so the change it causes appears only after the event has ended
   • The response opposes the original change, so the variable is pulled back towards its normal value

3. Which term describes the stable internal conditions maintained by the body despite external changes?

   • Homeostasis, the maintenance of a relatively constant internal environment within narrow limits despite external change
   • Transcription, the process by which the sequence of a gene is copied into a strand of messenger RNA
   • Chemiosmosis, the movement of protons down their gradient through ATP synthase to produce ATP in mitochondria
   • Glycolysis, the breakdown of one glucose molecule into two molecules of pyruvate in the cytoplasm

4. Which brain region acts as the main controller of thermoregulation and other homeostatic functions?

   • Medulla oblongata only, which controls heart rate and breathing but has little role in temperature control
   • Corpus callosum, which connects the two cerebral hemispheres and passes information between them
   • Hypothalamus, which monitors body temperature and other internal conditions and co-ordinates responses to keep them near set points
   • Cerebellum, which co-ordinates balance, posture and the smooth timing of voluntary movements in the limbs

5. During exercise, which response helps to lose excess body heat?

   • Shivering to generate heat, which uses rapid muscle contractions to release heat from respiration in the muscles
   • Sweating and vasodilation of skin arterioles, which cool the skin by evaporation and bring warm blood to the surface
   • Decreased breathing rate, which reduces the loss of water vapour and so keeps the body warmer during activity
   • Vasoconstriction of skin arterioles, which reduces blood flow to the skin and so limits the loss of heat from the body

6. Which of the following is an example of a negative feedback loop during exercise?

   • Blood clotting produces more clotting factor, which speeds up clotting and so increases the production of further factor
   • Oxytocin during childbirth increases uterine contractions, which lead to the release of even more oxytocin
   • Rising body temperature causes sweating, which cools the body and so lowers the temperature back towards its set point
   • Contractions of the uterus stimulate more oxytocin release, which in turn produces stronger contractions still

7. Which example shows positive feedback?

   • Oxytocin released during labour increasing uterine contractions, which release more oxytocin and intensify labour
   • Sweating reducing body temperature, which brings the temperature back down towards its normal value
   • Insulin lowering blood glucose after a meal, which returns the glucose level towards its normal set point
   • Increased blood pressure triggering baroreceptors to slow the heart, which brings the blood pressure back down

8. A runner's core temperature rises from 37.0 degrees C to 38.5 degrees C. Which change would be a negative feedback response that brings the temperature back down?

   • Increased shivering, which generates heat through rapid muscle contractions and so raises the core temperature
   • Constriction of arterioles in the skin, which conserves heat in the body and keeps the core temperature high
   • Reduced blood flow to the skin, which keeps warm blood in the core and so raises the temperature further
   • Increased sweating and dilation of skin blood vessels, which increase heat loss and reverse the rise in temperature

9. During exercise, what is the effect of an increase in carbon dioxide concentration in the blood on breathing?

   • Breathing rate increases, which removes carbon dioxide from the blood and brings the level back down
   • Breathing rate decreases, since carbon dioxide acts as a depressant on the ventilation centre in the medulla
   • Breathing rate stays the same, since carbon dioxide has no effect on the signals sent by the chemoreceptors
   • Breathing stops completely, since carbon dioxide blocks the nerves that carry signals to the breathing muscles

10. Why is negative feedback described as maintaining systems within narrow limits?

    • Because it allows large swings in the variable to occur without any correction, so the variable can drift freely
    • Because it ends the control process as soon as it starts, so the variable is left wherever the change began
    • Because it works only at very high temperatures, so it is effective only during extreme heat exposure
    • Because it corrects deviations from the set point quickly, so the variable stays close to the set point

11. A person's blood glucose is 5.5 mmol per dm^3 and rises to 7.0 mmol per dm^3 after a meal. Which response is an example of negative feedback?

    • Glucose rises because more insulin is released into the blood, which raises the level further after the meal
    • Glucose remains at 7.0 because the pancreas stops responding to the raised level, so the value stays high
    • Glucose rises further as glycogen is broken down in the liver, which raises the blood glucose level higher still
    • Glucose falls to 5.5 after insulin is released from the pancreas, which lowers glucose back towards the set point

12. Which statement best describes the set point in homeostasis?

    • The maximum value that a variable can reach before the body is damaged by the change in the internal conditions
    • The rate at which a hormone is secreted into the bloodstream by the gland that produces it in response to stimulus
    • The time it takes for a stimulus to reach a receptor and be converted into a nerve impulse by the neurone
    • The optimum value around which the controlled variable is maintained by the feedback mechanisms of the body

13. Which component of a homeostatic control system detects a change in the controlled variable?

    • Receptor, which detects changes in the internal environment and sends information to a control centre
    • Hormone target, which is the cell that responds to a hormone circulating in the blood
    • Effector, which carries out the response, such as contraction of a muscle or secretion from a gland
    • Enzyme, which catalyses reactions within cells and is not involved in detecting changes in the environment

14. During exercise, a rise in blood temperature is detected and the heat-loss response is switched on. Which sequence correctly describes this control system?

    • Control centre, effector, stimulus, receptor, in which the control centre gives orders before the change happens
    • Effector, receptor, control centre, stimulus, in which the response is carried out before any change is detected
    • Receptor, stimulus, effector, control centre, in which the effector acts before the control centre is involved
    • Stimulus, receptor, control centre, effector, response, in which the change is detected and then corrected by the body

15. A student states that feedback in the body always keeps variables constant. Which evaluation is best?

    • Partly incorrect, because positive feedback drives change rather than stability, and negative feedback only keeps variables within limits
    • Correct, because positive feedback always reverses the stimulus, so every variable returns to its original value
    • Correct, because feedback never allows any change, so every variable stays exactly at its set point at all times
    • Incorrect, because feedback only works in plants and has no role in the control of animal body systems

16. Which statement describes the role of the hypothalamus during exercise?

    • It stores glycogen in liver cells, releasing glucose into the blood when the level falls during activity
    • It is the site where lactate is oxidised to carbon dioxide in the mitochondria of the liver cells
    • It produces adrenaline in the adrenal glands, which are located above the kidneys and release hormones into the blood
    • It monitors blood temperature and other internal conditions and co-ordinates responses such as sweating and shivering

17. A person's core temperature must be maintained at about 37 degrees C. During cold exposure, which response increases heat production?

    • Shivering, which uses rapid muscle contractions and respiration in the muscles to release heat
    • Sweating, which cools the skin by evaporation of water from the surface and so reduces the core temperature
    • Vasodilation of skin arterioles, which brings warm blood to the skin surface and so increases heat loss
    • Increased blood flow to the skin surface, which carries heat away from the core to the external environment

18. Consider a set point of 37 degrees C. A person's temperature is 36 degrees C. Which response would be expected from a negative feedback loop?

    • Vasoconstriction of skin vessels and shivering to raise temperature, which conserves heat and produces more of it
    • Vasodilation of skin vessels to lose heat, which carries warm blood to the surface and increases heat loss
    • Sweating to reduce temperature further, which cools the body and moves it further away from the set point
    • A fall in heart rate to lower temperature, which reduces the metabolic rate and so cools the body down

19. Which statement describes how negative feedback can produce oscillation around a set point?

    • It operates only when the set point is above 50 degrees C, and so it has no effect at normal body temperatures
    • It amplifies change until the organism is harmed, so the variable moves steadily away from the set point
    • It produces a stable value with no change at any time, so the variable stays exactly on the set point
    • Responses can overshoot the set point, causing the variable to swing above and below it before settling

20. A student explains a homeostatic response in exercise as follows: the rise in temperature triggers sweating, which stops the rise. Which principle does the explanation illustrate?

    • A hormone with no effect on the target, since sweating is not controlled by any chemical signal in the body
    • Positive feedback in which the response amplifies the change, so the temperature rises even more steeply
    • Negative feedback in which the response opposes the change, so the temperature is brought back towards normal
    • Random variation without any control mechanism, since the temperature changes only by chance during activity

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