Variation

Slide 1

• VARIATION

Slide 2

• Organisms are adapted to survive in different conditions. Over many generations, these adaptations have come about through variation. Variation involves small changes between organisms which may allow that organism to compete better for survival. Variation can have environmental or genetic causes.

Slide 3

• 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.

Slide 4

• Cold climates Every organism has certain features or characteristics that allow it to live successfully in its habitat. These features are called adaptations, and we say that the organism is adapted to its habitat.Organisms living in different 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.

Slide 5

• 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 its predators 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 leaves. 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.
• A pompeii worm
• The Pompeii worm is adapted to the high temperatures and pressures of the hydrothermal vents by:
• using a thick layer of bacteria to protect it from heat
• hiding inside a papery tube to protect it from predators.

Slide 6

• Variation Some of the features of the different organisms in a species show continuousvariation, 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. So it 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.

Slide 7

• Discontinuous 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.

Slide 8

• 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 pods
• count 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.

Slide 9

• Causes of variation Some variation within a species is inherited, and some variation is 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 information 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.

Slide 10

• 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.
• 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 of inherited 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.