Homeostasis, feedback and thermoregulationEdexcel A-Level Biology A: Subtopic test

1. 1
   A runner begins a 10 km race on a warm, humid morning. As her muscles respire faster, they release large amounts of heat and her core body temperature starts to rise above its normal value of about 37 °C.

   (a)

   Which part of the brain monitors the temperature of the blood and coordinates the body's responses to a rise in temperature?

   [1 mark]

   • ACerebellum
   • BMedulla oblongata
   • CHypothalamus
   • DCerebral cortex

   (b)

   Which response of the skin helps the runner to lose heat?

   [1 mark]

   • AVasoconstriction of skin arterioles
   • BContraction of the erector pili muscles
   • CShivering of skeletal muscle
   • DVasodilation of skin arterioles

   (c)

   Explain how sweating helps to lower the runner's body temperature.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Physiologists compare two types of control system in the human body. In one, a rise in core temperature triggers responses that bring the temperature back down. In the other, during childbirth, stretching of the cervix stimulates the release of the hormone oxytocin, which strengthens uterine contractions, which in turn stretch the cervix further.

   (a)

   Which statement correctly identifies the childbirth process described as a type of feedback?

   [1 mark]

   • APositive feedback, because the change in the stimulus is amplified
   • BNegative feedback, because the contractions reverse the stretching of the cervix
   • CNegative feedback, because oxytocin is a hormone
   • DPositive feedback, because it keeps the cervix at a constant stretch

   (b)

   Which sequence shows the correct order of components in a negative feedback loop controlling core temperature?

   [1 mark]

   • AEffector, coordinator, receptor, stimulus
   • BStimulus, receptor, coordinator, effector
   • CStimulus, coordinator, receptor, effector
   • DReceptor, stimulus, effector, coordinator

   (c)

   Explain why positive feedback cannot be used to keep body temperature stable.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A runner is monitored during 60 minutes of steady running. Her core temperature rises from 37.0 °C to 38.4 °C over the first 25 minutes and then stays at 38.4 °C for the rest of the run. Over the same period the blood flow through her skin increases from 0.30 dm³ min⁻¹ at rest to 2.40 dm³ min⁻¹.

   (a)

   Calculate the percentage increase in the blood flow through the runner's skin between rest and the end of the run.

   [3 marks]

   (b)

   Explain how the data show that the body temperature is controlled by homeostasis, and why her core temperature stops rising after 25 minutes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hill walker is crossing exposed moorland on a cold, windy day in light clothing. Her core body temperature begins to fall below its normal value. A mountain rescue doctor later explains to her how her body responded and why maintaining a stable temperature is so important.

   (a)

   Explain how her body responds to the fall in core temperature to restore it to its normal value.

   [6 marks]

   (b)

   Evaluate the importance of homeostasis and negative feedback in maintaining a stable body temperature, including what could happen if control failed.

   [6 marks]

   Total for question 4: 12 marks

End of questions