Selection and evolution — AS & A Level Biology (9700) questions by topic
Natural selection, speciation and Hardy-Weinberg calculations anchor this topic: describing how a random mutation gives rise to a selection-favoured trait, distinguishing sympatric from allopatric speciation, and working out the number of heterozygous plants from an allele frequency. Suggest, explain and outline lead the command words, and outline wants each stage of a selection or speciation process listed in the correct order, not just the outcome named.
This set has 20 real questions from 2023 to 2025 papers, and marks run from 6 to 16, so most answers require several linked points of reasoning rather than a single fact. Practising selection and speciation explanations with instant marking is useful here, since describing mutation as directed by need, rather than random, is flagged immediately rather than repeated.
What examiners look for
- A recurring error misunderstands 'random' in natural selection, suggesting a trait arises because organisms need to escape predators.
- The term 'allele frequency' is sometimes misused, for example stating that better-adapted organisms directly increase their own allele frequencies.
- Allopatric speciation is occasionally named where the two populations' ranges actually overlap in the present day, which points to a different mechanism.
- Hardy-Weinberg calculations sometimes use q as the given frequency directly instead of taking its square root, or use pq instead of 2pq for heterozygotes.
- Strong answers state that the selection pressure favours individuals with the beneficial trait, name the correct type of speciation with supporting detail, and correctly apply the Hardy-Weinberg principle including the square-root step.
May–June 2025, Paper 41
Geospiza fortis is one of the many species of finch that live on the Galápagos islands. Scientists measured the bill size (length, width and depth) of individuals in a population…
Answer this question and get it marked →May–June 2025, Paper 42
When organisms reproduce, they pass on their alleles to the next generation. There are many factors that can affect how allele frequencies change over time in a population.…
Answer this question and get it marked →May–June 2025, Paper 43
The Grand Canyon is located in Arizona, USA, formed as the Colorado River created a deep channel in the surrounding rocks. Before the canyon formed, an ancestral species of…
Answer this question and get it marked →May–June 2024, Paper 41
White-clawed crayfish, Austropotamobius pallipes, live in rivers and lakes in Europe. In the 1850s, the North American signal crayfish, Pacifastacus leniusculus, was introduced to…
Answer this question and get it marked →It has been hypothesised that the mutation rate of an animal species may affect how fast animals of that species age and how long they live (lifespan). Table 7.1 compares the…
Answer this question and get it marked →The harlequin ladybird, Harmonia axyridis, is an insect that shows discontinuous variation in colour pattern and continuous variation in body size. Within a species, the variation…
Answer this question and get it marked →May–June 2024, Paper 42
Variation exists in populations of a species and this may provide the opportunity for evolution to occur. Phenotypic variation exists in many forms and has a number of possible…
Answer this question and get it marked →May–June 2024, Paper 43
Phenotypic variation exists in many forms. Some examples of phenotypic variation in plants and animals are described in Table 2.1. Complete Table 2.1 by stating whether the cause…
Answer this question and get it marked →October–November 2024, Paper 42
Several different processes can affect allele frequencies in populations. Outline the processes that may affect allele frequencies in wildlife populations.
Answer this question and get it marked →Phenotypic variation exists in natural populations. There are many causes of variation. Natural selection determines which phenotypes are advantageous. Variation in a particular…
Answer this question and get it marked →October–November 2024, Paper 43
Spea multiplicata is one of several species of American spadefoot toad. Young spadefoot toads are called tadpoles and live in water in ponds. S. multiplicata tadpoles show three…
Answer this question and get it marked →May–June 2023, Paper 41
Pyruvate carboxylase (PC) deficiency is a rare disease. The rate of respiration in the cells of a person with PC deficiency is much lower than normal. The passage describes the…
Answer this question and get it marked →May–June 2023, Paper 42
A large sample of sea blush fruits was collected and their fruit-wing characteristic was recorded. Name the type of variation that is shown for the fruit-wing characteristic of…
Answer this question and get it marked →Use Hardy-Weinberg equation 1 and equation 2 to calculate the percentage of the population of rats on the island that is heterozygous for warfarin resistance. equation 1: p + q =…
Answer this question and get it marked →May–June 2023, Paper 43
Humans use antibiotics to treat bacterial infections. The increased use of antibiotics has led to an increase in the number of strains of bacteria that are resistant to…
Answer this question and get it marked →October–November 2023, Paper 41
There are more than 600 plant species in the genus Ipomoea. The gene that determines flower colour in Ipomoea purpurea (common morning glory) has two alleles: a dominant allele…
Answer this question and get it marked →Green lacewings are a family of insects with more than 1300 species. Green lacewings have sense organs, known as tympanal organs, that detect sound. The tympanal organ of green…
Answer this question and get it marked →October–November 2023, Paper 42
Research suggests that selective breeding began about 10 000 years ago and has been important in satisfying the global demand for food. The introduction of disease resistance to…
Answer this question and get it marked →October–November 2023, Paper 43
There are more than 600 plant species in the genus Ipomoea. Many species are grown for their attractive flowers, and some species are used as crop plants. Fig. 3.1 shows Ipomoea…
Answer this question and get it marked →Green lacewings are a family of insects with more than 1300 species. The common green lacewing, Chrysoperla carnea, is shown in Fig. 9.1. Green lacewings have sense organs, known…
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