02 Variation

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- GCSE Bitesize - Variation

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Science

Variation

Organisms are adapted to survive in different conditions.

Over many generations, these adaptations have come about

through variation. Variation involves small changesbetween organisms which may allow that organism to

compete better for survival. Variation can have

environmental or genetic causes.

Adaptation

Darwin's theory of evolution explains how species of living things

have changed over geological time. The theory is supported by

evidence from fossils and by the rapid changes that can be seen

to occur in microorganisms such as antibiotic-resistant bacteria.

Many species have become extinct in the past, and the

extinction of species continues to happen.

Cold climates

Every organism has certain features or characteristics that allow

t to live successfully in its habitat. These features are called

adaptations, and we say that the organism is adapted to its

habitathabitat:A place where plants, animals and

microorganisms live..Organisms l iving in di fferent habitats

need different adaptations.

The polar bear

Polar bears are well adapted for survival in the Arctic. They

have:

a white appearance, as camouflage from prey on the

snow and ice

thick layers of fat and fur, for insulation against the cold

a small surface area to volume ratio, to minimise heat

loss

a greasy coat, which sheds water after swimming.


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Watch more polar bear videos on BBC Nature, and discover

how well polar bears and their cubs are adapted to the extreme

environment they live in.

The snowshoe hare

The snowshoe hare has white fur in the winter and reddish-

brown fur in the summer. This means that it is camouflaged from

ts predatorspredators:Animals that hunt, kill and eat other

animals for food. for most of the year.

Arctic plants

The Arctic is cold and windy with very little rainfall. Plants in the

Arctic often grow very close to the ground and have small

eaves. This helps to conserve water and to avoid damage by

the wind.

Extreme environments

Some organisms are adapted to extreme environments : for

example, deep sea hydrothermal vents.

The Pompeii worm is adapted to the

high temperatures and pressures of

the hydrothermal vents by:

The polar bear is adapted to life in a cold climate
http://www.bbc.co.uk/nature/life/polar_bearhttp://www.bbc.co.uk/nature/life/polar_bear


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using a thick layer of bacteria to

protect it from heat

hiding inside a papery tube toprotect it from predators.

In an exam you will need to be

able to describe the variation and

explain how i t helps the organism

to survive.

Variation

Some of the features of the different organisms in a species

show continuous variation, and some features show

discontinuous variation.

Continuous variation

Human height is an example of continuous variation. Height

ranges from that of the shortest person in the world to that of the

tallest person. Any height is possible between these values. Sot is continuous variation.

For any species a characteristic that changes gradually over a

range of values shows continuous variation. Examples of such

characteristics are:

height

weight

foot length.

f you record the heights of a group of people and draw a graph

of your results, it usually looks something like this:

A pompeii worm


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The more people you measure, and the smaller the categoriesyou use, the closer the results will be to the curved line. This

shape of graph is typical of a feature with continuous variation.

Weight and foot length would give graphs similar in shape to

this.

Discont inuous variation

Human blood group is an example of discontinuous variation.

There are only four types of blood group. There are no other

possibilities and there are no values in between. So this is

discontinuous variation.

A characteristic of any species with only a limited number of

possible values shows discontinuous variation. Here are some

examples of discontinuous variation:

gender (male or female)blood group (A, B, AB or O)

eye colour.

Height variation graph


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Investigating variation

Variation within a species can be investigated. For example, if

you were asked to find out if there was a link between the length

of a pea pod and the number of seeds inside the pod you could:

measure the length of a range of pea podscount the peas inside.

The experiment is made valid by controlling the variables .

The independent variable is length of the pea pod.

The dependant variable is the number of peas.

The control variables include:

variety of pea plant

time of year that the peas are selected.

The experiment is made reliable by further testing and

achieveing a repeat of your results.

Causes of variation

Some variation within a species is inherited, and some variation

Blood groups variation graph


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s due to the environment.

Inherited causes of variation

Variation in a characteristic that is a result of genetic inheritance

from the parents is called inherited variation.

Children usually look a little like their father, and a little like their

mother, but they will not be identical to either of their parents.

This is because they get half of their inherited features from each

parent.

Each egg cell and each sperm cell contains half of the genetic

nformation needed for an individual. When these join at

fertilisation a new cell is formed with all the genetic information

needed for an individual.

Here are some examples of inherited variation in humans:

eye colour

hair colour

skin colour

lobed or lobeless ears.

Gender is inherited variation too, because whether you are male

or female is a result of the genes you inherited from your

parents.


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Environmental causes of variation

Characteristics of animal and plant species can be affected by

factors such as climate, diet, accidents, culture and lifestyle. For

example, if you eat too much you will become heavier, and if

you eat too little you will become lighter. A plant in the shade of

a big tree will will grow taller as it tries to reach more light.

Whether you have lobed or lobeless ears is due to genetic causes


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Variation caused by the surroundings is called environmental

variation . Here are some other examples of features that show

environmental variation:

language and religion

flower colour in hydrangeas - these plants produce blue

flowers in acidic soil and pink flowers in alkaline soil.Both types together

Some features vary because of a mixture ofinherited causes

and environmental causes. For example, identical twins inherit

exactly the same features from their parents. But if you take a

pair of twins, and twin 'A' is given more to eat than twin 'B', twin

A' is likely to end up heavier.

Now try a Test Bite.

Back to Revision Bite
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/classification_inheritance/variation/quiz/q19540345/http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/classification_inheritance/variationrev1.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/classification_inheritance/variationrev1.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/classification_inheritance/variation/quiz/q19540345/

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