Homeostasis and temperature control — Edexcel GCSE Biology

Revision notes

4 short notes, in the order of the specification. Each one in short:

1. Maintaining a constant internal environment

   Homeostasis is maintaining a constant internal environment in response to internal and external change. The body keeps blood glucose concentration, body temperature and the water content of the blood within narrow limits. This matters because enzymes and cells work best in a narrow range of conditions. Many of these controls use negative feedback.

2. Thermoregulation and osmoregulation

   Triple only

   Thermoregulation is the control of body temperature at about 37°C, the optimum for most enzymes: too hot and enzymes are denatured, too cold and reactions are too slow. Osmoregulation is the control of the water content of the blood. If the blood is too dilute, water enters animal cells by osmosis and they swell; too concentrated, and they shrink.

3. The skin and the hypothalamus

   Triple only

   The hypothalamus in the brain is the control centre for body temperature. It monitors the temperature of the blood and receives impulses from temperature receptors in the dermis of the skin. It then sends nerve impulses to effectors such as the sweat glands, muscles and blood vessels. Sweat reaches the skin surface through pores in the epidermis.

4. Responses to heat and cold

   Triple only

   When the body is too hot, sweat glands release sweat, which evaporates and takes heat from the skin. In vasodilation, the blood vessels supplying the skin widen, so more heat is lost. When the body is too cold, shivering muscles contract rapidly and respiration transfers energy as heat, sweating is reduced, and vasoconstriction narrows the vessels to reduce heat loss.