Chapter 29: Homeostasis

Leaving Certificate BiologyHigher Level

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

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.

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.

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

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

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.