Homeostasis and feedbackEdexcel International A Level Biology: Flashcards

Exam questions on Homeostasis and feedback

1. The core body temperature of a healthy human is maintained close to 37 °C, even when the temperature of the surroundings changes from day to day. A physiologist records the core temperature of a volunteer every minute for several hours and finds that it fluctuates by a small amount above and below 37 °C.
   Explain why homeostasis is described as maintaining dynamic equilibrium.2 marks
2. During childbirth, the baby's head presses on the cervix at the base of the uterus and stretches it. Stretch receptors in the cervix send impulses to the brain, which causes the release of the hormone oxytocin into the blood. Oxytocin stimulates the muscle of the uterus to contract more strongly, which pushes the baby's head harder against the cervix.
   Explain why positive feedback is not used to maintain body temperature.2 marks
3. A marathon runner's core body temperature was monitored throughout a training run. Before the run it was 37.0 °C. It rose to 38.6 °C after 40 minutes and then stayed between 38.6 °C and 38.8 °C for the rest of the run. Her sweat rate rose from 0.05 dm³ per hour at rest to 1.2 dm³ per hour during the run, and the blood flow through her skin rose from 0.25 dm³ per minute at rest to 2.5 dm³ per minute.
   Explain how the hypothalamus brings about the changes in sweating and skin blood flow shown in the data.3 marks