Homeostasis and feedbackEdexcel A-Level Biology B: Mind map

Exam questions on Homeostasis and feedback

1. A student records the core body temperature of a healthy volunteer every hour for 24 hours. The temperature fluctuates between 36.4 °C and 37.2 °C, with an average of about 37 °C, even though the volunteer is active during the day and rests at night.
   Explain why a fall in core temperature well below 37 °C would slow the rate of enzyme-controlled reactions in cells.2 marks
2. On a hot day, thermoreceptors in the hypothalamus detect a rise in core body temperature. Nerve impulses lead to the sweat glands secreting more sweat and to the arterioles supplying the skin capillaries dilating. Core body temperature falls back towards 37 °C and the sweating then decreases.
   Explain how the dilation of the arterioles in the skin helps to reduce core body temperature.2 marks
3. During labour, the stretching of the cervix by the baby's head stimulates the release of the hormone oxytocin from the pituitary gland. Oxytocin causes stronger contractions of the uterus muscle. The stronger contractions push the baby's head harder against the cervix, causing more stretching and more oxytocin release. This continues until the baby is born.
   Explain why this is an example of positive feedback.3 marks