CCEA GCSE Biology 2.5 Variation and Natural Selection Exam Questions

About CCEA GCSE Biology 2.5 Variation and Natural Selection

Variation and Natural Selection is a Unit 2 topic in CCEA GCSE Biology that builds on genetics and meiosis. You need to distinguish continuous from discontinuous variation and present each on the right kind of graph, and explain how variation is caused by genes, the environment or both. The topic then covers how natural selection leads to evolution, using examples such as antibiotic resistance in bacteria, and how humans use selective breeding to produce plants and animals with useful characteristics. It links to topic 2.6, where antibiotic resistance appears again. Examiners often ask for natural selection explanations in clear stages and comparisons of natural and selective breeding.

What you need to know

• Types of variation Continuous variation has a range of values with no distinct groups, for example height or mass, and is shown on a histogram. Discontinuous variation has distinct categories, for example blood group or tongue rolling, and is shown on a bar chart.
• Causes of variation Genetic variation comes from meiosis, random fertilisation and mutation. Environmental factors such as diet, climate and lifestyle also cause variation; many characteristics, such as height, are affected by both.
• Mutation A mutation is a random change in the DNA or in chromosome number or structure. Most have no effect or are harmful, but a few are beneficial. The rate is increased by ionising radiation and some chemicals.
• Natural selection There is variation in a population and more offspring are produced than can survive. Individuals compete, and those with advantageous characteristics are more likely to survive and reproduce, passing on their alleles. Over many generations these alleles become more common in the population, which is evolution.
• Antibiotic resistance as an example A random mutation may make a bacterium resistant to an antibiotic. When the antibiotic is used, non-resistant bacteria die while resistant bacteria survive, reproduce and pass on the resistance allele, so the resistant strain spreads.
• Selective breeding Humans choose parents with desired characteristics (for example high milk yield or disease resistance), breed them and select the best offspring over many generations. It reduces genetic variation and can increase the risk of inherited disease.

Common mistakes in 2.5 Variation and Natural Selection

• Writing that organisms change or mutate in order to adapt. Mutations are random; selection then favours the useful ones.
• Saying that bacteria become immune to antibiotics. The correct term is resistant, and it is the population that changes.
• Missing the inheritance step in natural selection. Say the survivors reproduce and pass on their alleles to offspring.
• Plotting continuous data on a bar chart. Continuous variation is shown on a histogram with no gaps between bars.
• Treating selective breeding as natural selection. In selective breeding humans choose which individuals breed.

Try three 2.5 Variation and Natural Selection exam-style questions