OCR GCSE Biology A: Sexual and asexual reproduction, haploid and diploid cells and meiosis (J247) – 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 statements B5.1f, B5.1g and B5.1h of the OCR GCSE (9-1) Biology A Gateway Science specification (J247), Version 4.0, for first assessment in 2018. No statement in this unit is Higher Tier only. Revise first with the study guide and the revision notes. Course links: the OCR GCSE Biology hub, the printable checklist and the free diagnostics.

Questions

1. Human skin cells have 46 chromosomes. (a) How many chromosomes does one human egg cell have? [1] (b) State the number of chromosomes in a human zygote. [1] (c) Give the term for a cell that contains chromosomes in pairs. [1]

2. The table shows the number of chromosomes in body cells of four mammals.

Mammal	Chromosomes in a body cell	Chromosomes in a sperm cell
Cat	38
Mouse	40
Chimpanzee	48
Horse	64

(a) Complete the last column. [2] (b) Explain why the number in a body cell of a mammal is always an even number. [2]

3. Give two differences between the offspring produced by asexual reproduction and the offspring produced by sexual reproduction. [2]

4. A bacterium divides by binary fission every 15 minutes. Assume that no cells die. (a) Calculate the number of bacteria after 2 hours from a single cell. [2] (b) A mouse produces a litter of several young. Suggest why a mouse cannot increase its numbers as fast as the bacterium. [2]

5. A farmer grows strawberries by planting runners from existing plants. A new fungal disease reaches the farm. (a) Explain why all of the plants may be killed. [3] (b) Suggest two advantages to the farmer of using runners instead of seeds. [2]

6. Describe what happens to the number of chromosomes in meiosis, and explain why this is necessary. [3]

7. Complete the table to compare mitosis and meiosis. [5]

	Mitosis	Meiosis
Number of cells made from one cell
Chromosome number of cells made
Genetically identical or different
One use in a human
Where in a flowering plant	all growing tissues

8. The table gives information about three species. The data are supplied for this question. Assume each adult breeds at the stated rate for the whole 12 years.

Species	Young per birth	Births per year
P	7	4
Q	1	0.33
R	2	1

(a) Calculate how many young one adult of species P produces in 12 years. [2] (b) One adult of species Q has one birth every 3 years. Work out how many young it produces in 12 years, and the ratio of the young produced by P to the young produced by Q. [3] (c) Suggest one disadvantage to species Q of its low number of young. [1]

9. A fruit fly has 8 chromosomes in a body cell. (a) State the number in a gamete. [1] (b) Calculate how many different combinations of chromosomes are possible in the gametes of one fly, if each pair separates independently. [2] (c) Calculate the probability that a gamete contains the four chromosomes that came from the fly’s father. [2] (d) Explain what your answer to part (b) shows about the offspring of two flies. [1]

10. Explain how meiosis and fertilisation together keep the chromosome number of a species the same in every generation, and how meiosis produces genetic variation. [5]

11. A gardener can grow a variety of daffodil from bulbs that split to form new bulbs, or from seeds produced by flowers. Evaluate which method the gardener should use (i) to grow a large number of flowers that are all the same colour as the parent, and (ii) to start a wild flower meadow in a region where the climate is getting warmer. [6]

12. Maize has 20 chromosomes in a leaf cell. (a) State how many chromosomes are in (i) a pollen nucleus and (ii) the zygote formed after fertilisation. [2] (b) Calculate the number of different combinations of chromosomes possible in the pollen nuclei of one plant, assuming only independent separation of pairs. [2] (c) Calculate the probability that a pollen nucleus has all of its chromosomes from the plant’s maternal parent. Give your answer to 3 significant figures. [2] (d) Explain why a cell with 10 chromosomes can only be a gamete and not a leaf cell. [2]

Answers

1. (a) 23 [1] [1] (b) 46 [1] [1] (c) Diploid [1] [1] Examiner insight: A bare number is enough for a one-mark recall question, but writing “23 pairs” for a gamete shows a pair/set confusion, so say “23 chromosomes”.

2. (a) Halve each number: cat 19 [1], mouse 20, chimpanzee 24, horse 32 [1] [2] (b) Chromosomes are in pairs [1], one of each pair from the mother and one from the father, so the total is twice the number of pairs [1] [2] Examiner insight: For “explain” questions, give the reason (pairs, one from each parent) rather than only restating that the number is even.

3. Asexual offspring are genetically identical to the parent, and sexual offspring are genetically different from both parents [1]. Asexual offspring come from one parent, sexual offspring from two parents, or from the fusion of two gametes [1]. [2] Examiner insight: Two separate differences are needed, so do not give two versions of the same point such as “identical” and “the same”.

4. (a) 2 hours = 120 min, and 120 ÷ 15 = 8 divisions [1]. 2⁸ = 256 bacteria [1] [2] (b) A mouse must find a mate and reproduce sexually, and has only a limited number of young in each litter [1]. A mouse also needs a gestation period before each birth, whereas a bacterium doubles in number on every division [1] [2] Examiner insight: A calculation worked out in steps lets a slip in counting divisions be seen separately from the doubling.

5. (a) Plants grown from runners are genetically identical to the parent [1]. They all share the same weaknesses, so a pathogen that can infect one can infect all of them [1]. There is no variation, so there are no resistant plants that survive and reproduce [1] [3] (b) One mark each for two of: one parent is enough; the new plants have the same useful features, such as fruit size, as the parent; the plants grow without waiting for seeds [1] [1] [2] Examiner insight: A link from “identical” to “same weakness” to “the disease affects all” is what scores. Saying “no variation” on its own does not explain the risk.

6. The number is halved [1], from the diploid number to the haploid number in the gametes [1]. This is necessary so that when two gametes fuse in fertilisation the diploid number is restored, and does not double each generation [1] [3] Examiner insight: “Halved” plus a reason scores. A statement of only “makes gametes” does not answer a question about chromosome number.

7. Mitosis two cells, meiosis four cells [1]. Mitosis same as the parent cell (diploid), meiosis half (haploid) [1]. Mitosis identical, meiosis different [1]. Mitosis: growth or repair, meiosis: making gametes (sperm and egg) [1]. Meiosis in the anthers and ovules [1] [5] Examiner insight: In a table, a short precise word such as “diploid” or “haploid” is better than a vague one such as “same”.

8. (a) Births in 12 years = 4 × 12 = 48 [1]. Young = 48 × 7 = 336 [1] [2] (b) Births = 12 ÷ 3 = 4, and 4 × 1 = 4 young [1]. Ratio P : Q = 336 : 4 [1] = 84 : 1 [1] [3] (c) Any one: the population increases only slowly, so it takes a long time to recover if it is reduced by disease or hunting, or if numbers fall [1] [1] Examiner insight: Show the number of births before multiplying by young per birth, and give a ratio in its simplest form.

9. (a) 4 [1] [1] (b) There are 4 pairs and 2 choices per pair, so 2 × 2 × 2 × 2 [1] = 2⁴ = 16 [1] [2] (c) The chance for each pair is 1/2, so the probability is (1/2)⁴ [1] = 1/16 = 0.0625 [1] [2] (d) Each parent can produce many different gametes, so offspring from the same parents differ genetically [1] [1] Examiner insight: A power of 2 with the number of pairs, not the number of chromosomes, is the common route to a correct result.

10. Meiosis halves the chromosome number, producing haploid gametes [1]. Fertilisation fuses two haploid gametes [1] so the zygote is diploid, restoring the original number [1]. In meiosis the pairs of chromosomes separate independently, so every gamete gets its own combination of chromosomes from the two parents [1]. Any sperm can fuse with any egg, adding to the variation [1] [5] Examiner insight: Questions with two demands, such as number and variation, need both parts answered. Give each part its own sentence.

11. (i) Bulbs [1]. They are clones, so all the flowers will be the same colour as the parent [1]. Bulbs also avoid the need for pollination [1]. (ii) Seeds [1]. Seeds are produced by sexual reproduction, so they vary [1]. Some seedlings are more likely to survive in a warmer climate and can then reproduce, so the meadow persists [1] [6] Examiner insight: An evaluation should reach a clear choice for each situation, supported by a reason that is linked to the situation.

12. (a) (i) 10 [1] (ii) 20 [1] [2] (b) There are 10 pairs, so 2¹⁰ [1] = 1024 [1] [2] (c) (1/2)¹⁰ [1] = 0.000977 (9.77 × 10⁻⁴) [1] [2] (d) A leaf cell is diploid and has 20 chromosomes [1]. A cell with 10 is haploid, which is the number in a gamete [1] [2] Examiner insight: A very small probability is best given in standard form or as a fraction, and 3 significant figures means three digits starting from the first non-zero digit.

Where marks are usually lost

• Writing “46 pairs” or “23 pairs” for gametes instead of 23 chromosomes.
• Calling asexual offspring “the same” without saying genetic information, and calling sexual offspring “different” without a reason.
• Saying meiosis makes two cells or that it keeps the number the same.
• Explaining the risk to a crop of clones without linking to a shared weakness.
• Using the number of chromosomes, rather than the number of pairs, as the power of 2.
• Treating sexual reproduction as simply “better”, or asexual reproduction as “worse”.
• Not stating that fertilisation restores the diploid number.
• Giving a probability as a decimal that is rounded too early.
• Leaving out the situation in an evaluate question.

Next steps

• Review with the revision notes and the study guide.
• Open the OCR GCSE Biology hub and tick off statements on the printable checklist.
• Try the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OCR GCSE (9-1) Biology A (Gateway Science) specification J247, Version 4.0 (August 2026), for first assessment in 2018, published by OCR: statements B5.1f, B5.1g and B5.1h.