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Biology for Secondary Schools

Thermoregulation sufficient internal heat, they rely on
behaviours such as basking in the sun
Task 5.4
Search from the library and internet or seeking shade to control their body
sources animations about mechanism temperature.
of thermoregulation in mammals. Watch Temperature regulation in endotherms
FOR ONLINE READING ONLY
the animations and prepare a summary. In order to keep their stable body

temperature, endotherms have mechanisms
Thermoregulation is the process by
which organisms maintain their internal and structures to detect temperature
body temperature within a certain range, changes. They also have a mechanism to
despite changes in external environmental restore the internal body temperature to
temperatures. This process is crucial for its normal level. Temperature changes are
survival, as extreme temperatures can detected by sensory cells located in the skin.
disrupt metabolic processes and impair The changes in temperature stimulate the
cellular functions. Thermoregulation sensory cells which in turn initiate impulses
ensures that enzymatic reactions occur at in sensory nerve endings. These impulses
optimal rates, allowing the body to function are sent to the brain’s thermoregulatory
efficiently. centre. The thermoregulatory centre
interprets these changes and sets off

Thermoregulation mechanisms in a series of body reactions which may
organisms either lead to an increase or decrease in
temperature. When the temperature of the
Organisms regulate their body temperature surrounding environment is lower than the
through different mechanisms. Based on the body temperature, animals lose heat to the
strategies or mechanisms used, different surroundings. Heat is lost from the body
organisms are grouped into two types: surface through radiation, evaporation and

Endotherms: These are animals that conduction. See Figure 5.4.
generate body heat through internal
metabolic processes. Mammals and birds Response to cold conditions
are the main examples of endotherms. When the temperature of the surroundings is
They use physiological mechanisms such low, the temperature of the animal begins to
as sweating, shivering, and metabolic fall. In order to raise the body temperature
adjustments to maintain a stable body to its normal level, the body of the animal
temperature. responds by one or more of the following
actions:
Ectotherms (cold-blooded animals): These
animals depend on external environmental Increased metabolic rate: The body
sources to regulate their body temperature. increases its metabolic activities,
Reptiles, amphibians, and fish are examples particularly in the liver and muscles, to
of ectotherms. Since they do not produce generate heat. Hormones such as thyroxine

110 Student’s Book - Form Three

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