ADAPTATIONS including extremophiles

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 groups

(1) Structural adaptations

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 on prey!

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 themselves!

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

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!

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 reduced

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 respiration.

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.

(2) Behavioural adaptations

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 sweating).

(3) Functional adaptations

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 excretion process.

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 salts.

The above examples plus others are further discussed below along with the sort of learning objectives you need to cope with.

  • (a) Know and understand that to survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.

  • (b) Know and understand that plants often compete with each other for light and space, and for water and nutrients from the soil.

  • (c) 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 competition.

    • 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).

  • (d) Know and understand that organisms, including microorganisms have features (adaptations) that enable them to survive in the conditions in which they normally live.

  • (e) 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

      • Some deep sea fish can  give out light from organs on their body's surface like the angler fish which has rod-shaped spine sticking out from its face which emits light to attract prey.

  • (f) Know and understand animals and plants may be adapted for survival in the conditions where they normally live, eg deserts, the Arctic.

    • Know and understand that animals may be adapted for survival in dry and arctic environments by means of:

      • Changes to surface area - heat/water transfer factor

        • Increasing (in hot environments) or reducing heat (in cold environments) transfer from organisms is an important adaptation to help survival.

        • Desert animals eg in Africa, tend to have a large surface area/volume ratio to allow excess body heat to be readily lost. This helps overheating, particularly as they do not sweat much and produce smaller volumes of concentrated urine, both helping to reduce water loss.

        • Animals living in very cold climates eg the arctic regions and northern Europe and Russia, tend to have a smaller surface area/volume ratio to minimise heat loss. Their bodies need to compact with a minimum volume - 'roundish' to minimise the surface area through which heat is lost.

        • The arctic fox and wolves have short ears and a short snout to minimise surface area, hence minimise heat loss.

      • Thickness of insulating coat

        • Desert animals have thinner coats than animals in colder climates, which aids heat loss.

        • Animals living very cold climates have thick hairy coats to minimise heat loss, but the fur must be in good condition to trap insulating air and keep cold water away from the skin. The fur of animals like the arctic fox is an extremely good insulator and can survive at temperatures as low as -50oC. It has a long winter coat with thick dense underfur. Bears, similarly, have thick fur coats.

      • Amount of body fat

        • Desert animals have thin layers of body fat compared to animals in colder climates, which aids heat loss.

        • Animals in arctic regions have thick layers of insulating fat or blubber AND these also act as an important energy store - fat/blubber has a very high calorific value, useful in lean times and scarcity of food. eg seals, penguins, polar bears, whales

      • Camouflage

        • Desert animals have sand coloured coats which give good camouflage to minimise being seen and attacked by predators, it also the enables animal to a predator itself, prey becomes the hunter!

        • Arctic animals like polar bears have white fair to blend in with the icy/snowy background to increase the chances of a kill. Smaller white coated animals are less likely to seen and caught. The white arctic fox is a mean hunter! Birds like the ptarmigan stand a better chance of survival from predators turning white in colour in winter, and brown in the summer, thereby blending into the landscape with the change in seasons

  • (g) Know and understand that plants may be adapted to survive in dry environments by means of eg examples of structural adaptations ...

    • 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, plants like cacti have a rounded shape with thin spines instead of broader leaves.

    • water-storage tissues

      • Plants like cacti have relatively thick fleshy stems which contain groups of specialised cells that store water. 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.

    • 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.

  • (h) Know and understand that animals and 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.

    • Some insects and other animals have very bright 'warning' colours to look 'fearful' to potential predators e.g. wasps

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