Why will identical twins not be exactly alike in later life?
Mutations in DNA as each foetus develops. Environmental factors can contribute to physical characteristics.
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What is intraspecific variation?
Members of the same species show variation.
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What is interspecific variation?
Differences between members of different species.
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What is continuous variation?
Where a full range of intermediate phenotypes exist between 2 extremes. Most individuals are close to the mean value.
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What is discontinuous variation?
There are 2 or more distinct groups of phenotypes with little overlap. Members of a species may be evenly distributed or there may be more of one type than another.
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Give one cause of variation.
The genes we inherit from our parents help define our characteristics. We inherit one set of alleles from each parent.
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How many genes are there in human cells?
About 25,000.
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Give another cause of variation.
Many characteristics are affected by the environment. But the effect of environment can't completely override the effect of genes. The genes have a limiting effect.
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What does continuous variation indicate?
It indicates characteristics that are influenced by several genes and the environment.
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What does discontinuous variation indicate?
It indicates characteristics that are influenced by one or two genes with little or no environmental influence.
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What is an adaptation?
It is any variation that helps an organism to survive.
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Give some important adaptations for survival.
Find enough water, gather enough nutrients, survive physical conditions, defend against predators and disease.
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What is a behavioural adaptation?
An aspect of the behaviour of an organism that helps it to survive the conditions it lives in.
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What is a physiological/biochemical adaptation?
One that ensures the correct functioning of cell processes.
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What is an anatomical adaptation?
Any structure that enhances the survival of an organism.
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Give 2 behavioural adaptations of xerophytes.
They can close their stomata when water is in short supply. They can roll up their leaves to reduce surface area for transpiration.
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Give a physiological adaptation of xerophytes.
The mechanism involved in the plant being able to close its stomata.
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Give 4 anatomical adaptations of xerophytes.
Long root system to reach water deep underground, fleshy stems to store water when it's available, waxy cuticle to reduce evaporation of water, hairs around stomata to keep a layer of moist air to reduce the water potential gradient.
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