V.C.E. Biology Unit 2
Temperature Regulation and Water
Balance
Vascular Plants
 Plants are not able to maintain body
temperature or water balance to the
same degree as animals.
 However, they have many
adaptations which allow for the
control of water levels:
Transpiration
Stomata
Waxy Cuticles
 Thick bark allows plants to insulate
themselves from heat and the use of
stomata allow for some control of the
loss of heat to the environment and
gas exchange of course
Body Temperature in Animals
 Ectothermic – animals other than birds and mammals
that are unable to control their body temperature.
 They produce less heat from their metabolism and
lose it more rapidly to the environment.
Ectotherms bask in the sun to
increase their internal
temperature and are inactive at
night and in cold weather
hibernating during particularly
cold winters by entering a state
known as torpor
Body Temperature in Animals
 Endothermic animals are mostly birds and mammals.
They maintain a relatively constant internal
temperature that is generally greater than the
external environment.
 Endotherms have insulation such as feathers, fur or
hair and layers of fat to reduce heat loss to the
environment.
 They also use various physiological and behavioural
means (such as hibernation) to regulate heat gain
and loss.
Temperature Regulation Pathways
 The regulation of temperature requires a complex set
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of negative feedback pathways. These include:
Behavioural responses – putting on and taking off
clothes, moving into and out of shade
Physiological responses – shivering, sweating,
panting, constriction or dilation of blood vessels
Structural – counter current flow, thermal windows,
fur and skin colouration.
Thermoreceptors are found in the skin and also
internally to monitor the temperature of the internal
environment and the external environment.
Water Balance
 Terrestrial animals are
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able to respond to falls
and rises in water
content by a number of
means:
Drink more water
Use water in food
Use metabolic water
Remove water from the
urine – loop of Henle
Remove water from the
faeces – large intestine
Water Balance
 For marine and freshwater animals there are other
difficulties
 Freshwater fish and frogs rarely drink water as
freshwater moves on an osmotic gradient into their
bodies and thus produce a great deal of dilute urine –
this is an example of a hypotonic situation
 Saltwater fish have the opposite problem, they drink
regularly as water is constantly moving out of their
bodies on an osmotic gradient – this is an example of
a hypertonic situation.
Isotonic
Hypertonic
Hypotonic