Doc Brown's Biology Revision Notes
Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent
You should appreciate that organisms are well adapted to survive in their normal,
but often very different environments. Adaptations are features of an organism
that make it better suited to live and prosper in its environment.
Using your knowledge
and understanding you should be able to suggest how organisms are adapted to the
conditions in which they live. Organisms that are better adapted to their
environment are more able to compete for food resources.
Know examples of adaptations, eg body shape,
colour and other structural features of a range
of organisms from different habitats and understand the ways in which
adaptations enable organisms to survive in different habitats and produce
fertile offspring enabling the species to continue to exist, further reproduce
to pass on their adaptations.
You should be able to explain how organisms are adapted to their environment and how some organisms
have characteristics that enable them to survive in extreme environments,
including deep-sea hydrothermal vents and polar regions.
In studying these examples you should know and understand that organisms, including
microorganisms have features (adaptations) that enable them to survive in
the conditions in which they normally live and some cases understand that some organisms
have adapted to live in
environments that are very extreme.
Adaptations can be classified into three
This applies to features of organism's
body structure, anatomical adaptations e.g. colour, shape, nature of outer
body layers etc.
Arctic animals like the arctic fox and
polar bears have white fur for camouflage against the background of snow and
offer some protection against predators, but also allows the fox to sneak up
Animals living in cold climates like
polar bears have thick layers of fur to trap a good insulating layer of warm
air next to the skin. As well as a thick hairy coat the fur is 'greased'
from glands in the skin and this greasy fur lets water run off easily so
there is less water to evaporate giving a cooling effect. Its the same for
seabirds and penguins who must keep their wing feathers oily.
Many desert animals have sand coloured
fur to give good camouflage protection from predators or to act as predators
Animals in very cold climates, like
whales (mammals), seals and penguins in polar oceans, have a thick layer of
blubber (fat) and a low surface area to volume ratio (from nearly the most
compact shape) to help reduce heat loss through the skin. The blubber acts
as an insulator to retain body heat. Its the same argument applies to the
bodies of seals, penguins and polar bears.
The greater the surface area the
greater the rate of heat transfer. The most compact shape to give the
lowest surface area/volume ratio is a sphere, but that's no good for
swimming efficiently through oceans, so a rounded streamlined fish shape
is a good compromise! The polar bear is large but reasonably compact
bearing it mind it needs arms and legs to walk, swim and hunt!
A bit of area/volume maths to
illustrate this adaptation with cubes of various sizes (6 faces/sides):
A 1 cm cube has a volume
of 1 cm3 (1 x 1 x 1), a surface are of 6 x 1 x 1 = 6 cm2
So the surface area / volume
ratio = 6 / 1 = 6 cm-1
A 2 cm cube has a volume
of 8 cm3 (2 x 2 x 2), a surface are of 6 x 2 x 2 = 24 cm2
So the surface area / volume
ratio = 24 / 8 = 3 cm-1
A 3 cm cube has a volume
of 27 cm3 (3 x 3 x 3), a surface are of 6 x 3 x 3 = 54 cm2
So the surface area / volume
ratio = 54 / 27 = 2 cm-1
You can see clearly that the smaller
(thinner etc.) of the animal the greater the surface to volume ratio and
the greater the rate of heat loss.
So, you can clearly see the advantage
of a compact shape minimising the surface area for larger animals i.e.
to minimise heat loss in large animals like polar bears, but the fat
layer and fur help too!
You completely reverse the argument
when dealing with the transport of substances in multi-cellular
organisms, when you want the most efficient transfer system possible for
one or more functions of the organisms.
Diffusion, osmosis and active transport and
Examples of exchange surfaces
The blubber in whales and seals is also a
great store of energy for the whale and other species like seals.
Animals that live in very hot climates eg
desert camels, only have a thin layer of fat and a large surface area to
volume ratio to lose excess body heat efficiently. Most a camel's fat
(energy store) is in the hump which means the rest of the body doesn't need
a layer of insulating fat that would reduce heat loss through the skin. A
camel's fur layer is also thinner so too much heat is not retained.
Birds have wings to fly and fish and
penguins have flippers/fins to propel themselves by swimming. Some fish tail
fins are large in surface area to increase traction, but other fins are
smaller and adapted to help stability when moving fast through water.
Large heavy animals like polar bears have
large flattish feet to spread their weight more evenly and reducing their
sinking into snow and falling through ice.
A physics note in biology!:
pressure = force (weight) / surface area, increase area, pressure
Seals, penguins and many fish have
streamlined bodies adapted for swimming. The streamlining reduces water
resistance, friction, (just like an aircraft's shape reduces air resistance)
and enables the creature to escape from predators OR catch some prey!
Giraffes have long tall necks to eat
leaves that other animals can't reach.
Fish have gills, which have a large
surface area, to extract oxygen (at low concentration) from water for
Fish have an organ called a swim bladder
containing gas, and the volume can be adjusted to enable the fish to change
its depth in the water without having to use valuable energy.
Animals like penguins standing on cold
ice, have blood vessels through which the flow is in opposite directions and
these vessels pass close to each other and allow heat transfer between them.
Warm blood flows in the arteries to heat up the feet and cold blood returns
to the heart in the veins. The feet are still relatively cold but it stops
cold blood from cooling down the body.
Many animals in hot environments, by
being small, have a large surface area to volume ratio which helps them keep
cool by losing more heat through the skin. Also, large thin ears with a
large surface area and lots of blood vessels have the same effect increase
heat loss by conduction and radiation.
These describe how an organism behaves
to adapt to its environment e.g.
Many animals migrate from colder to
warmer climates (maybe to breed) and return at the end of the season e.g.
birds like ducks and swallows. By migration many species avoid the harshness
and dangers of a cold climate.
Penguins huddle together to keep each
other warm in the frozen wastes or the Arctic and Antarctic. On average
there is less body surface area exposed to the cold air and winds.
Many desert animals live for much of
their time in burrows underground where there is more moisture and cooler
out of direct sunlight. Other animals rest in the shade particularly in the
middle hottest parts of the day to minimise the absorption of heat.
Minimising excessive heat gain can be helped by being more active
(hunting-feeding) in the cooler nighttime.
Many animals have adapted hibernate over
winter to conserve energy and not have to go hunting for prey in harsh
conditions with little prey around. In these very cold climates, animals
like bears, lower their rate of metabolism to a point where very little food
(energy) is needed to keep alive and they go into a deep sleep and wake in
the spring when life supporting conditions are much better. A very sleepy
way to save energy!
In hot countries animals can increase
their heat loss and cool down by bathing in water. Not only does the water
absorb heat, but evaporation from the skin absorbs heat energy (just like in
These are features of an organisms
body that relate to the fundamental processes such as reproduction and
metabolism (some of the most important chemical reactions in the body).
In very dry arid conditions e.g. desert
animals may conserve water by having a specialised kidney that produces very
small amounts of concentrated urine.
So very little water is used in the
Such animals may not have sweat
glands so there is no water loss from sweating evaporation.
Organisms eg animals like penguins (with
feet on ice!), are helped to survive in extreme cold conditions (<0oC)
by producing antifreeze proteins in their tissue fluids. Rather like putting
salt on roads, they reduce the chance of ice crystals forming that would
otherwise damage cell structure.
More on examples of adaptations and extremophiles
Don't forget that microorganisms, like
bacteria, live in a huge variety of environments, some of them in quite extreme
conditions and not surprisingly they are called extremophiles! Some
microorganisms live on very hot rocks eg by hot volcanic vents and some exist
under very pressure and temperature in the deep ocean volcanic vents. Some
bacteria can live in water containing very high concentration of dissolved
The above examples plus others are further
discussed below along with the sort of learning objectives you need to cope
Know and understand that to survive and reproduce,
organisms require a supply of materials from their surroundings and from the
other living organisms there.
Know and understand that plants often compete with
each other for light and space, and for water and nutrients from the soil.
Know and understand that animals often compete with
each other for food, water, mates and territory.
In the wild territorial
disputes between species or members of a species are common - an example of
Those animals who are best adapted will nudge out of other
species from a particular habitat.
In most UK woodlands, the grey
squirrel from North America, has displaced the native red squirrel,
principally because it out-competes for food. The grey squirrel can feed
more at ground level and can digest acorns and red squirrels can't).
Know and understand that organisms, including
microorganisms have features (adaptations) that enable them to survive in
the conditions in which they normally live.
Know and understand that some organisms live in
environments that are very extreme.
Know that so-called extremophiles
may be tolerant to high levels of salt, high temperatures, high pressures or
adapted to extremes of pH.
Flamingos filter-feed on brine
shrimp and blue-green algae and their pink or reddish colour comes from
carotenoid proteins in their diet of animal and plant plankton which can
survive in the very salty lakes the flamingos fly to for feeding.
Some microorganisms can survive in very
acid water (low pH <<7) or very alkaline water (high pH >>7)
There are certain microorganisms, eg
bacteria colonies, that live by hot volcanic vents of water on land (eg
geysers) or on the seabed (where the vents are called 'black smokers'). The
bacteria cannot rely on photosynthesis so they make there own food by using
chemical energy derived from the minerals on and around the vent. These
processes are called chemosynthesis, powered by chemical energy, as opposed
to photosynthesis in plants powered by sunlight. These bacteria then become
the producers for a food chain that can support several animal species - so
we still have food chains and food webs in these extreme conditions. These
bacteria must be adapted to cope with both high temperatures and high
pressures in extreme depths of the ocean in volcanically active regions.
Biochemical point: Extremophile bacteria
living in very hot water have enzymes whose optimum operating temperature is
much higher than 'normal' for most organisms e.g. ours is ~37oC.
The high temperatures encountered eg by deep oceanic volcanic vents
would normally denature the protein structure of enzymes, but the enzymes
have evolved and adapted to higher ambient temperatures.
There are creatures that happily
live on the deep ocean beds where the pressure from the water above is
enormous. Deep sea fish often have large mouths to collect scraps of food
from the seabed and/or have large eyes to cope with dim light conditions
to see prey and some deep sea creatures have long feelers to detect prey.
It should be pointed out that deep in
seas and oceans there is virtually no light, the depth being such that
sunlight doesn't penetrate to the sea or ocean bed. This means no plants
because of no light for photosynthesis. Therefore deep sea organisms have to
rely on scraps of food that sink down from richer regions of life. This hard
life has produced some interesting adaptations eg
Know and understand animals and plants may be adapted for survival in
the conditions where they normally live, eg deserts,
Adaptations in plants
Know and understand that plants may be adapted to survive in dry environments
by means of eg examples of structural adaptations ...
Plants are adapted to live in a variety of environments including extreme environments that are very hot
and/or very dry like deserts.
These adaptations affect, in
particular, the size and shape of a plant's leaves, cuticle and the
number and position of the stomata.
Changes to surface area, particularly of the leaves
- through which water is naturally lost by transpiration
To reduce the surface area, to
reduce water loss by evaporation, plants like cacti have a rounded shape with thin spines instead of broader
Other plants have smaller leaves.
Spines also deter animals from
feeding on the plants like cacti.
Plants like cacti, living in deserts,
tend to have adaptations which help them to conserve water - retain as
much water as they have access too.
Plants like cacti have
relatively thick fleshy stems which contain groups of specialised cells that
Some giant cacti like the saguaro cactus in the deserts of
Arizona (USA) can be 20m high and hold in storage several tonnes of water -
more than enough to see it through the driest of dry seasons and survive
long periods of drought.
Cacti also have a water repellent
thick waxy layer (the cuticle) which further reduces water loss by
Leaves can be curled or have hairs on
their surface. This reduces air flow over the leaf keeping more water
vapour near the surface and so reducing the diffusion of water vapour
from the leaf surface to the surrounding air. Spines also have a similar
effect in reducing air flow.
Plants with fewer stomata on their
leaves or have stomata that only open at night are adaptations that
reduce water loss.
Stomata can be sunk in pits, so being
below the leaf surface, they do not experience the same flow of air as
the surface and so less water vapour carried away - helping water
Extensive root systems
Cacti generally have one of
two kinds of root system. (i) Some have relatively few roots, but roots
that can burrow deep into the ground to seek out underground water. (ii)
Most other cacti have many shallow spread out roots that can rapidly absorb
water quickly over a large area eg if it rains, which may be very infrequent in desert regions.
Know and understand that plants may be adapted to cope with
specific features of their environment, these specialised features to deter
predators include thorns,
poisons and warning colours to deter predators eg
Roses have thorns, hedgehogs
have needle like spikes/spines over the upper side of their body and can
curl up to give all round protection, cacti have sharp spines to deter
animals (herbivores) eating them, turtles, armadillos and tortoises have
hard protective shells. These are examples of organisms having a sort of
'armour' for protection!
Plants like ivy contain poisons,
insects like bees and wasps have stings, some desert shrubs secrete toxic
compounds into the soil to prevent other plants growing nearby.
Plant diseases and defences against pathogens
and pests gcse biology revision notes
explained, limiting factors affecting rate, leaf adaptations
gcse biology revision notes
Plant cells, transport and gas exchange in plants,
transpiration, absorption of nutrients, leaf and root structure
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