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Chapter 29: Homeostasis
Leaving Certificate Biology
Higher Level
• Homeostasis is the maintenance of a
constant internal environment
– Factors that need to be controlled:
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
• Osmoregulation is the maintenance of the
correct amount of water in the living
• 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
• 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