OxfordAQA International GCSE Biology: Variation, natural selection and species (9201) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover sections 3.6.1 and 3.6.2 a to c (variation and natural selection) of the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams in May/June 2018 onwards. The qualification is untiered. Related pages: the course hub, the printable checklist and the free diagnostics.

Questions

1. Two children have the same parents but different hair colour.

(a) Explain why sexual reproduction leads to genetic variation in offspring. [3] (b) A strawberry plant sends out runners, and each runner grows into a new plant. Explain why the plants grown from runners have the same genes as the parent. [2]

2. A gardener took six cuttings from one tomato plant and grew them in two groups. Group P had extra potassium in the compost. Group R had none. The heights after five weeks are shown.

Group	Height of each cutting / cm
P	31, 29, 33, 30, 32, 31
R	22, 24, 21, 25, 23, 23

(a) The mean height of group P is 31.0 cm. Calculate the mean height of group R. [2] (b) The cuttings all came from one plant. Explain what the difference in means shows about the cause of the difference in height. [2] (c) Explain why the heights within group R are not all the same, even though the cuttings are genetically identical. [1]

3. Researchers grew 1000 seedlings from untreated seeds and 1000 seedlings from seeds exposed to a high dose of X-rays. They counted the seedlings with an unusual leaf shape: 3 from untreated seeds and 11 from the exposed seeds.

(a) Describe what a mutation is. [1] (b) Calculate how many times greater the number of unusual seedlings was in the exposed group. Round your answer to two significant figures. [2] (c) Suggest what the results show about the effect of X-rays. [1]

4. For each characteristic, state whether the variation is mainly genetic, mainly environmental, or a combination of both. Give a reason in each case.

(a) A scar on a person’s knee. [1] (b) A person’s ABO blood group. [1] (c) The body mass of an adult. [1]

5. The ancestors of a species of cave beetle lived above ground and had large eyes. The modern cave beetles have very small eyes.

(a) Describe how Lamarck’s theory would explain the small eyes. [2] (b) In the cave, beetles with smaller eyes were more likely to survive and breed than beetles with larger eyes. Explain how natural selection led to small eyes. [3] (c) Give one reason why Lamarck’s explanation is not accepted for most inherited characteristics. [1]

6. A wild grass grows on land beside an old mine. The soil contains a metal that kills most grass seedlings. Over many years, a higher proportion of the seedlings in that soil survived. Explain how natural selection could have caused this change. [5]

7. A storm destroyed the shelter in a woodland. Insects with longer wings could fly to a new shelter more easily. The table shows 400 insects measured before the storm and the number alive afterwards.

Wing length / mm	Number before storm	Number alive afterwards
11	40	2
13	120	18
15	160	64
17	80	56

(a) Calculate the percentage of insects with wings of 11 mm and of 17 mm that were alive after the storm. [2] (b) Calculate the percentage of all 400 insects that were alive afterwards. [1] (c) Describe the pattern shown by the data. [2] (d) A scientist says the next generation will have longer wings on average. State the condition that must be true for this to happen, and explain why. [2]

8. A bacterium divides into two every 30 minutes. Assume none die and the first division is at 30 minutes. A species of large mammal has a generation time of 25 years.

(a) Calculate the number of bacteria after 6 hours, starting from one cell. [2] (b) Calculate how many hours the bacterium needs to pass through 40 generations. [2] (c) Explain, using your answers, why changes caused by natural selection can be seen in bacteria within a human lifetime but not in large mammals. [3]

9. A tree frog species lives on both sides of a valley. A new mountain range rises across the valley. One side becomes wet and the other becomes dry. The frogs can no longer cross the mountains. Describe, using the four stages in order, how this could lead to two species of frog. [5]

10. A species of beetle lives on a single large island. Rising sea level splits it into islands A and B. The table shows the percentage of beetles with long antennae on each island after the split.

Generation	0	20	40	60	80
Island A: % with long antennae	10	14	22	35	52
Island B: % with long antennae	10	9	7	5	3

(a) Describe the changes shown for each island. [2] (b) Calculate the percentage increase in beetles with long antennae on island A from generation 0 to generation 80. [2] (c) Suggest an explanation for the difference between the two islands. [3] (d) Beetles from the two islands were brought together after 1000 generations. They could mate, but no fertile offspring were produced. Explain what this shows and why the populations became different. [3]

Answers

1. (a) Each parent produces gametes that carry different combinations of alleles [1]. Any male gamete can fuse with any female gamete, so each child gets a different mixture [1]. Genetic information from two parents is mixed, so offspring differ from each other and from the parents [1] [3] (b) Runners are asexual reproduction, with one parent and no fusion of gametes [1]. There is no mixing of genetic information, so the new plants are clones with the same genes [1] [2] Examiner insight: Naming the process (fusion of gametes, mixing of alleles) usually earns more credit than “they get genes from both”.

2. (a) Total = 22 + 24 + 21 + 25 + 23 + 23 = 138 [1]. Mean = 138 / 6 = 23.0 cm [1] [2] (b) The difference is 31.0 - 23.0 = 8.0 cm [1]. The cuttings have identical genes, so the difference is caused by the environment, the potassium [1] [2] (c) Small differences in light or water affect each cutting [1] [1] Examiner insight: Quote the 8.0 cm difference and say that the genes are identical. A conclusion that does not mention the clones is a weaker answer.

3. (a) A change in a gene (the genetic material) that produces a new allele [1] [1] (b) 11 / 3 = 3.67 [1], which is 3.7 times to 2 significant figures [1] [2] (c) X-rays increase the rate of mutation (the frequency of mutants) [1] [1] Examiner insight: Write the unrounded value first and round in the last line.

4. (a) Environmental: a scar is acquired during life and is not inherited [1] [1] (b) Genetic: blood group is controlled by inherited alleles [1] [1] (c) A combination: it depends on inherited alleles and also on diet and activity [1] [1] Examiner insight: A classification with no reason is easy to lose.

5. (a) Lamarck’s idea is that changes during an organism’s life are inherited [1]. The beetles’ eyes became smaller through lack of use in the dark, and this change was passed to the young [1] [2] (b) Beetles varied in eye size because of different alleles [1]. Beetles with smaller eyes were more likely to survive and breed [1]. They passed on the alleles for small eyes, so these alleles became more common over generations [1] [3] (c) Changes acquired during life do not alter the alleles in the gametes, so in the vast majority of cases they cannot be inherited [1] [1] Examiner insight: In part (b), start with variation that already existed. “Lost their eyes because they were not needed” repeats Lamarck’s idea.

6. Seedlings varied because of different alleles, and a few had alleles that let them tolerate the metal [1]. Tolerant seedlings were more likely to survive in the contaminated soil, while non-tolerant seedlings were killed [1]. Survivors grew to flower and produce seed (they bred successfully) [1]. They passed on the alleles for tolerance in their seeds [1]. Over many generations, the proportion of tolerant plants rose, so a higher proportion of seedlings survived [1] [5] Examiner insight: Each link in the chain (variation, survival, breeding, passing on alleles, change in proportion) is a separate point.

7. (a) 11 mm: 2 / 40 x 100 = 5.0% [1]. 17 mm: 56 / 80 x 100 = 70.0% [1] [2] (b) Total alive = 2 + 18 + 64 + 56 = 140. 140 / 400 x 100 = 35.0% [1] [1] (c) The percentage alive rises as wing length increases [1]. Quote values (5.0% at 11 mm, 70.0% at 17 mm) [1] [2] (d) The wing length must be genetic (controlled by alleles) [1]. Only then are the alleles for long wings passed to the offspring of the survivors, so they become more common [1] [2] Examiner insight: Convert counts to percentages before comparing classes, because the starting numbers differ.

8. (a) 6 hours = 12 divisions [1]. Number = 2^12 = 4096 [1] [2] (b) 40 x 30 min = 1200 min [1] = 20 hours [1] [2] (c) The mammal needs 40 x 25 = 1000 years for 40 generations [1]. Bacteria have a very short generation time, so many generations pass in a short time [1]. Useful alleles can become common within a human lifetime, but large mammals pass through only a few generations [1] [3] Examiner insight: Time-scale answers gain credit when they compare numbers of generations, not simply “bacteria are small”.

9. Isolation: the mountain range separates the two frog populations, so they stop interbreeding [1]. Genetic variation: each population has a wide range of alleles, and mutations add new ones [1]. Natural selection: the wet and dry environments differ, so different alleles that help survival are selected in each population [1]. Speciation: after many generations the two populations differ so much that matings between them no longer give fertile young [1]. The frogs are then two species [1] [5] Examiner insight: Give the stages in order and link natural selection to the different environments.

10. (a) Island A: the percentage with long antennae rises from 10% to 52% [1]. Island B: it falls from 10% to 3% [1] [2] (b) Increase = 52 - 10 = 42 [1]. Percentage increase = 42 / 10 x 100 = 420% [1] [2] (c) The islands have separate populations, and the environments are different, so different selection pressures act on each [1]. On island A, beetles with alleles for long antennae were more likely to survive and breed, so these alleles became more common [1]. On island B, beetles with long antennae were less likely to survive and breed, so the alleles became less common [1] [3] (d) The populations have become different species [1]. The sea isolated the populations, and natural selection in different environments acted on the alleles in each [1]. The populations became so different that successful interbreeding leading to fertile offspring is no longer possible [1] [3] Examiner insight: A percentage increase is found against the starting value. In part (c), say what was favoured on each island.

Where marks are usually lost

• Forgetting that survivors must breed for alleles to be passed on.
• Working out a percentage increase against the end value, when it should be against the start.
• Using Lamarck-type reasoning (use and disuse) to explain natural selection.
• Missing isolation from a speciation answer, or leaving out the fertile offspring test.

Next steps

• Revise with the revision notes.
• Re-read the study guide.
• Back to the OxfordAQA IGCSE Biology hub and the checklist.
• Try all the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams in May/June 2018 onwards, published by OxfordAQA. Section 3.6 Variation and evolution: 3.6.1 and 3.6.2 a to c.