Variation at Higher Level: The same statement as SL. At HL it leads into species that are hard to separate and into classification by clades, so be clear that variation within a species is smaller than between species.
Practise this as you read
- Outline what is meant by variation.
- Calculate a percentage from a chart of forms in a sample.
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The big idea: No two living things are exactly alike in all their traits. These differences are called variation.
The points to remember
- Variation means differences in traits between individuals.
- A trait is a feature, such as size, colour, shape, blood group or behaviour.
- No two individuals are identical in all their traits, even within one species.
- Even identical twins differ: their fingerprints are not the same.
- Variation is a defining feature of life: every living thing is a little different.
Remember it as: Same species, never the same beetle.
Real example: the harlequin ladybird: The harlequin ladybird, Harmonia axyridis, comes from Asia and has spread to Europe and North America. Some are orange with up to 19 black spots; others are black with two or four red spots. All are one species.
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The big idea: Biologists group organisms that share traits. The patterns of variation show where one group ends and the next begins.
The points to remember
- Members of one species share most traits: variation within a species is small.
- Different species differ in many more traits: variation between species is larger.
- These patterns of variation are the basis for naming and classifying organisms.
- The patterns are complex: some traits change gradually (height), others come in a few types (shell colour).
- So deciding where one group ends is not always clear.
Within one species
- Harlequin ladybirds: orange or black forms
- Same size and body plan
- Can all breed together
Between two species
- Harlequin v seven-spot ladybird (Coccinella septempunctata)
- Different size and spot pattern
- Many more traits differ
A different colour is not a different species: Individuals can look very different and still be one species. Count the shared traits, not the differences.
How it is tested: Paper 1B gives a chart of the forms in a sample: read the bar, then work out a percentage. Paper 2 can ask you to outline what variation is.
IB-style questionState / Calculate[2 marks]
A student counted harlequin ladybirds in one park by colour form. The bar chart shows a made-up sample of 200 beetles.
(a) State the most common colour form. [1]
(b) Calculate the percentage of the beetles that were black forms. [1]
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
Read the axis first: Check what one bar measures and the total in the sample before you calculate.