1. Chapter 29: Homeostasis Leaving Certificate Biology Higher Level

2. Homeostasis Homeostasis is the maintenance of a constant internal environment – Factors that need to be controlled: Temperature pH Glucose levels Water and salt levels (osmoregulation) Calcium levels

3. Temperature regulation Plants can survive in a range of temperatures. If it is too hot then transpiration increases. Also, heat shock proteins are produced to protect enzymes from excess heat. Animals can also resists quite large changes in temperature. There are two ways in which animals regulate internal temperature: – Ectotherm – animals whose internal temperature varies with their environment. – Endotherm – animals whose internal temperature does not change with external temperature.

4. pH regulation Enzymes are affected by changes in pH. Therefore, all living organism have to control their pH very carefully. In plants the pH of the soil determines whether or not the plant will grow. In animals pH can be controlled by the kidneys and by the respiratory system.

5. Glucose regulation Glucose levels, particularly in animals, must be maintained at certain levels. Too low and the animal will die; too high and the animal will develop diabetes. Glucose levels in animals are generally controlled by the pancreas and the hormone insulin

6. Osmoregulation Osmoregulation is the maintenance of the correct amount of water in the living organism. In plants, osmoregulation is carried out by the roots and by the process of transpiration. In animals, the amount of water in the body is controlled by the kidneys and lungs and too a lesser extent, the skin

7. Calcium regulation Calcium is a very important mineral for all living organisms. In plants it is used to make the middle lamella that holds plant cell walls together. In animals it is used as a major component of bone, but is also very important for the conduction of impulses to muscles. Calcium levels in animals are controlled by the parathyroids, by secreting the hormone parathormone.