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Size does matter!
• Size plays a vital role in the ammount of heat loss
or gain that an organism has with its
• Look at the diagram above. What is the
relationship between size and heat loss?
• As the body mass of an animal gets larger, the
rate of heat production for each unit of body
mass gets smaller.
• So again, which of the two animal loses more
heat to the environment?
• The answer is…
• The Long-tailed planigale.
• The larger animal, the Tammar wallaby maintains
its body temperature than the planigale as it has
a smaller surface are to volume ratio over which
it will lose heat to the environment.
Tolerance limits
• As we have discussed, different animals have
different rates of tolerance to environmental
• Tolerance to temperature depends largely on
the heat source for an organims.
• In other words, whether the animal is
ectothermic or endothermic.
• This describes animals that are unable to produce
their own body heat. These animals must obtain
their body heat from an external source.
• They are also incapable of maintaining a constant
internal environment (poikilothermic).
• Reptiles provide us with an example of animals
that are ectothermic.
• Answer the following questions.
• - What behavior do reptiles undertake to
uptake heat from their environment?
• - What would happen to a reptile if the
temperature stays very low for a long period
of time?
• Endothermic animals are those which have a built
in supply of body heat – internal energy releasing
chemical reactions that produce heat as energy.
• These animals also maintain a constant internal
environment (they are homeothermic).
• Examples of endothermic animals are mammals
and birds.
• Why do you think endotherms are able to tolerate greater variation
to their external environment in comparison to ectotherms?
• - Various terms are used to describe animals in relation to
their temperature. Distinguish between the following terms
and use named examples for each: ectotherm, endotherm,
homeotherm, poikilotherm.
- Do you think the terms ‘warm-blooded’ and ‘cold-blooded’
are appropriate descriptions for organisms? Justify your
- Apply the negative feedback model to explain
thermoregulation in mammals.
- What organs are involved in thermoregulation in mammals?
Key ideas
Animals surviving on land
• Organisms that live successfully in a habitat
would be expected to show particular
structural, behavioral and physiological
features or characteristics that assist them to
survive in the range of environmental
conditions that exist in that habitat.
• Read pages 317-320 and explain several
characteristics that allow animals to survive
a) the heat, and
b) the cold
Animals surviving in water
• The range of temperature variation in water is
far less than it is in terrestrial habitats.
• Whales and other mammals do not have fur,
they do however have very thick layers of
blubber, a special type of fat that acts like a
layer of insulation, keeping the heat in.
• Many fish produce anti-freeze, which keeps
the liquid in their cells from freezing in really
cold temperature waters.
Countercurrent systems
• Whales and mammals also maintain their body
temperature by using a countercurrent exchange
system. This is a fine network of vascular tissues
(capillaries) within fins and tails.
• An artery leading to the fin is paired with and
connected to a vein coming back from the fin.
Blood flowing back from the skin is cool, as it has
lost heat to the environment. In this system, the
cool blood returning gains heat from the warm
blood in the paired artery, so that this blood
returning to the vital organs does not cool them
too much.
Key ideas
Plant response to temperature change
Plants in a hot environment
- radiation
leaf shape
heat shock protein
leaf orientation
leaf fall
• Plants in a cold environment
• Unlike animals, plants cannot produce antifreeze.
• Because of the higher concentration of dissolved
ions in the cytosol of the plant cells, the freezing
point of the cytosol is lower.
Ice forms in the air space
surrounding the cells. The
ice pushes through the cell
walls, but does not break
the cell membrane.
Key ideas
Water balance in living organisms
• Water balance (osmoregulation) in mammals
• Kidneys control water balance in all vertebrates.
Water balance and blood pressure are closely
- increased water raises blood pressure
- decreased water lowers blood pressure
• The two significant compounds involved in water
regulation are:
- antidiuretic hormone (ADH) also known as
vasopressin and
• - renin
• Vasopressin is released by the hypothalamus as a
response to low blood pressure.
• It travels through the bloodstream to the kidney.
• Vasopressin acts specifically on the distal tubules of
the kidney, where it increases the amount of water
reabsorbed back into the blood stream at this site.
• Increase water in the blood = increased blood
• Increased drinking results in a feedback mechanism
to reduce the secretion of vassopressin.
• Renin is secreted by the kidneys when a person
becomes dehydrated, when their blood pressure
and blood volume falls.
• Renin works by increasing the active transport of
sodium ions from the urine being formed, back
into the blood.
• In accordance to the rules of osmosis, water will
follow the sodium, re-entering the bloodstream
and increasing the concentration of water in the
blood, which ultimately increases blood
• So, vassopressin and renin, although secreted
by different organs, work independantly
towards the same goal of increasing the
amount of water in the blood, thus increasing
blood pressure.
• They work together to restore water balance
as quickly as possible.
Water balance in other animals
Osmosis controls the movement
of water in and out of these single
celled organisms.
• Sea birds
• Birds conserve water by excreting uric acid – this
form of nitrogenous waste is the least toxic and
requires little water to be excreted with it.
• Sea birds also have salt glands above their eyes so
they can remove the salt from the salt water
which they drink and eliminate it from this gland.
• Reptiles
• Terrestrial goannas have a large number of kidney
tubules, to reabsorb water.
• Amphibians
• Frog have the problem of water coming in
through their skin. To combat this, they produce a
lot of urine.
Key ideas
Water balance in plants
• Water makes up about 90-95% of the living
tissues of plants. Most leaves are covered by a
waterproof waxy cuticle, through which relatively
little water is lost.
Although, when stomata are
open for gas exchange (CO2 in
and O2 out), water vapour is
lost to the atmosphere via the
process of transpiration.
• Ion concentration also play an important role in
stomatal aperture.
• What is the relationship between ion
concentration and stomatal aperture?
Factors that affect transpiration
Humidity is a major
factor that affects
movement of water out
of the leaves of plants.
If the air is dry, water
loss is far greater than
if the air is humid.
Why do you think this
• Wind also affects transpiration, whereby if it is
windier, the rate of water loss will be greater.
• Temperature is another factor that affects
transpiration, with higher the temperatures
resulting in greater water loss.
Structures to reduce water loss
- waxy cuticle
sunken stomata
rolled up leaves
cylindrical leaves
no leaves
• Chose two of these to explain in detail
Key ideas