A Level Biology (A2) chapter 6: Selection and evolution MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
48 exam-style questions on Selection and evolution, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Selection and evolution questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. An antibiotic was added to a culture of bacteria. The number of living bacteria fell sharply for several hours, then rose again, even though the antibiotic was still present. Which explanation is best?
A
the antibiotic had all been broken down
B
a few bacteria were already resistant; they survived and multiplied
C
the surviving bacteria were exposed to the antibiotic for long enough to develop resistance
D
the antibiotic made the survivors mutate
Show answer
Answer: B. With the antibiotic still present and working, only bacteria able to survive it can explain the rise. They were resistant before exposure because of a chance mutation; selection removed the rest, so the new population is mainly resistant.
2. A pair of identical twins raised in different homes as adults differ in body mass by 9 kg but have the same ABO blood group. Which conclusion is best supported?
A
body mass is determined only by genes, because identical twins have identical alleles
B
body mass is affected by environment and genes; blood group by genes only
C
blood group is affected by diet, but mass is not
D
identical twins inherit different alleles for body mass from each of their parents
Show answer
Answer: B. Identical twins have the same genotype, so a difference between them must be environmental, for example diet and exercise. ABO blood group is controlled by one gene and is not changed by the environment.
3. Before carrying out a t-test to compare mean leaf area in two populations of a plant, which null hypothesis should be stated?
A
the mean leaf area of one population is significantly greater than that of the other
B
there is a significant difference between the mean leaf areas of the two populations
C
leaf area is not correlated with population
D
there is no significant difference between the two mean leaf areas
Show answer
Answer: D. A null hypothesis always proposes no difference (or no relationship). The t-test then finds whether any difference between the means is too large to be put down to chance.
4. What is meant by allopatric speciation?
A
speciation within one area, caused by differences in courtship behaviour
B
speciation within one area, caused by populations using different food sources
C
speciation after populations are separated by a geographical barrier
D
speciation caused by selective breeding
Show answer
Answer: C. Allopatric speciation depends on geographical separation, such as a mountain range or sea, which stops gene flow between populations. Behavioural or ecological separation within the same area leads to sympatric speciation.
5. Why can antibiotic resistance spread quickly, even between different species of bacteria?
A
resistance genes are often on plasmids, which can pass between bacteria by conjugation
B
bacteria of different species interbreed
C
antibiotics act as mutagens that cause the same resistance mutation in all species
D
resistant bacteria release antibodies that protect other bacteria of any species nearby
Show answer
Answer: A. Plasmids carrying resistance genes can be transferred between bacteria by conjugation, including between different species (horizontal transfer), as well as being passed to daughter cells when bacteria divide.
6. How has resistance to a fungal disease been introduced into high-yielding varieties of wheat by selective breeding?
A
spraying the high-yielding variety with fungicide so that its offspring inherit resistance
B
crossing with a resistant variety, then selecting resistant, high-yielding offspring
C
exposing plants to the fungus so they make antibodies
D
growing it in one field until it adapts
Show answer
Answer: B. The resistance allele is brought in from a variety (often a wild or traditional one) that already has it; breeders cross the two and select, over several generations, offspring with both resistance and high yield. Plants do not make antibodies, and spraying does not change alleles.
7. Which statement describes discontinuous variation?
A
a histogram of the data forms a smooth bell-shaped curve
B
the characteristic is controlled by many genes with small additive effects
C
individuals fall into a few distinct categories with no intermediates
D
the characteristic is strongly affected by the environment
Show answer
Answer: C. In discontinuous variation each individual belongs to one clear class, such as blood group A, B, AB or O. A bell-shaped distribution, many additive genes and strong environmental influence are typical of continuous variation.
8. Why are maize plants inbred for several generations before two different inbred lines are crossed to produce hybrid seed?
A
inbreeding increases vigour, so the inbred lines themselves give the highest yields
B
inbreeding makes each line homozygous, so their F1 is uniform
C
inbreeding introduces new alleles
D
inbreeding makes the plants heterozygous at every locus before they are crossed
Show answer
Answer: B. Repeated self-pollination produces homozygous lines, so every gamete from one line is the same. Crossing two such lines gives F1 plants that are all identical and heterozygous. The inbred lines themselves are usually weak (inbreeding depression).
9. Two populations of a lizard are separated by a new river. Why may they eventually become two species?
A
the river causes adaptive mutations
B
each lizard changes its features during its lifetime to suit its side and passes these changes on
C
with no gene flow, their gene pools change independently until they cannot interbreed
D
smaller populations stop mutating
Show answer
Answer: C. Separated gene pools change independently: different mutations arise and are selected under different conditions, and drift acts by chance. If the populations later meet and cannot produce fertile offspring, they are separate species.
10. A t-test is used to compare the mean mass of seeds from two varieties, using a sample of 12 seeds of one variety and 15 seeds of the other. How many degrees of freedom should be used?
A
25
B
27
C
26
D
11
Show answer
Answer: A. For a t-test, degrees of freedom = n1 + n2 − 2 = 12 + 15 − 2 = 25. The formula c − 1 is used for chi-squared, not for the t-test.
48, each with the answer and a short explanation, across 3 topics: Variation, Natural and artificial selection, Evolution. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Biology (A2) chapter 6 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
