OxfordAQA International GCSE Biology 3.6 Variation and Evolution Exam Questions

About OxfordAQA International GCSE Biology 3.6 Variation and Evolution

Variation and Evolution is the final and shortest section of OxfordAQA International GCSE Biology, but it pulls together ideas from 3.5 Inheritance. You need to explain why individuals differ, separating genetic variation (from mutation and sexual reproduction) from environmental variation, and to tell continuous from discontinuous variation. You then explain evolution by natural selection, why Lamarck's theory of inheriting acquired characteristics is rejected, the long time scales involved, and how new species form through isolation. Examiners usually set extended answers asking you to explain how a feature evolved or how a population became two species, so practise writing the steps in a logical order.

What you need to know

• Causes of variation Differences between individuals can be genetic, environmental or a combination. Genetic variation comes from mutation and from sexual reproduction (meiosis and random fertilisation). Environmental variation produces acquired characteristics, such as a scar or a plant grown in shade.
• Continuous variation Continuous variation has a range of values with no distinct groups, for example height or mass. It is usually controlled by several genes plus the environment, and is plotted as a histogram or line graph.
• Discontinuous variation Discontinuous variation falls into distinct categories with nothing in between, for example ABO blood group. It is usually controlled by one or a few genes and is plotted as a bar chart.
• Natural selection Individuals in a species show genetic variation; those best suited to the environment are more likely to survive and breed; their alleles are passed on, so over many generations the advantageous characteristic becomes more common. Antibiotic resistant bacteria are a fast example.
• Lamarck Lamarck proposed that characteristics acquired during an organism's lifetime could be inherited. This does not happen in the vast majority of cases, so natural selection is the accepted theory.
• Time scales Evolution usually happens over very long periods, many generations, although organisms that reproduce quickly, such as bacteria, can change quickly.
• Speciation Populations become isolated, for example geographically; each has genetic variation; natural selection favours different alleles in each environment; over time they become so different they can no longer interbreed to produce fertile offspring.

Common mistakes in 3.6 Variation and Evolution

• Writing that organisms adapt or change because they need to. Variation already exists from mutation; the environment selects individuals that happen to have useful alleles.
• Saying the fittest are the strongest. Best suited means best adapted to that environment, which is what increases survival and breeding.
• Forgetting to mention that alleles or genes are passed on to offspring. Natural selection only changes a population if the advantageous alleles are inherited.
• Describing speciation as just geographical separation. You must say the populations change by natural selection until they cannot interbreed to produce fertile offspring.
• Plotting continuous data as a bar chart. Use a histogram for continuous variation and a bar chart for discontinuous variation.

Try three 3.6 Variation and Evolution exam-style questions