OCR A Level Biology A: Natural and artificial cloning (H420) – 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 section 6.2.1(a) to (d) of the OCR A Level Biology A (H420) specification, Version 4.1 (April 2026), for first assessment in 2025: natural and artificial clones in plants and animals, with the arguments for and against. Read the study guide first and keep the revision notes beside you. The OCR A Level Biology hub and the printable checklist list the rest of the course.

Questions

1. Describe how a potato plant reproduces by vegetative propagation and explain why the new plants are genetically identical to the parent. [3]

2. Describe how you would take and root a stem cutting from a Pelargonium. Give a reason for each of three steps. [6]

3. A grower treats cuttings with rooting powder containing auxin. Each group has 40 cuttings. After four weeks, 22 untreated cuttings have rooted, 31 cuttings treated with 0.1% auxin have rooted and 26 treated with 0.8% auxin have rooted.

(a) Calculate the percentage of cuttings that rooted in each group. [3] (b) Suggest one conclusion and one limitation of the investigation. [2]

4. Describe how micropropagation is used to produce many identical plantlets of a rare orchid from one parent plant. [6]

5. In a laboratory, every shoot is cut into 4 new shoots every 3 weeks, so the number is multiplied by 4 each cycle, starting from one shoot.

(a) Calculate the number of shoots after 15 weeks. [2] (b) The laboratory needs more than 20 000 shoots. Calculate the minimum number of weeks required. [2]

6. A nursery proposes to use micropropagation to supply a new ornamental shrub. Evaluate this proposal. [6]

7. Explain how identical (monozygotic) twins form in humans and why they may still differ in phenotype. [4]

8. Artificial embryo twinning is used to produce cattle.

(a) Describe how it is carried out. [4] (b) Explain why the calves are identical to each other but not to either parent. [2]

9. Dairy farmers use somatic cell nuclear transfer (SCNT) to clone a high-yielding cow.

(a) Describe the stages of SCNT. [5] (b) State whose nuclear DNA the clone carries and explain one way in which its genome is not identical to the donor of the somatic cell. [2]

10. In a trial of SCNT, 200 reconstructed eggs gave 80 embryos. 16 pregnancies followed, 6 births and 4 animals alive at one year.

(a) Calculate the percentage of reconstructed eggs that developed into embryos. [1] (b) Calculate the percentage of embryos that led to a pregnancy. [1] (c) Calculate the percentage of births that survived to one year. [1] (d) Suggest two concerns about SCNT that the data support. [2]

11. Evaluate the use of cloning of animals in agriculture and medicine, including issues of longevity. [8]

Answers

1. The potato tuber is a swollen underground stem that stores starch. [1] Buds (eyes) on the tuber grow into shoots, using the stored food, to form a new plant. [1] The cells are produced by mitosis without meiosis or fertilisation, so all have the same alleles as the parent. [1] [3] Examiner insight: Answers gain more credit when the structure is named correctly as a stem, and when mitosis is given as the reason for identity.

2. Cut a healthy shoot just below a node with a sharp, clean blade; the node region has tissue that can form roots. [1][1] Remove the lower leaves; this reduces water loss by transpiration. [1][1] Dip in rooting powder (auxin) and place in moist compost under a cover or in humid air; the auxin promotes root growth, and the humidity prevents wilting before roots can take up water. [1][1] [6] Examiner insight: Each step needs its own reason. A list of steps with no “because” leaves the explanation unfinished.

3. (a) Untreated: 22 ÷ 40 × 100 = 55%. [1] 0.1% auxin: 31 ÷ 40 × 100 = 77.5%. [1] 0.8% auxin: 26 ÷ 40 × 100 = 65%. [1] (b) Conclusion: auxin increased rooting, and 0.1% gave the highest percentage. [1] Limitation: one trial with one species and no repeats, so the difference could be chance. [1] [5] Examiner insight: Quote the percentages when you draw a conclusion, and name a specific limitation rather than writing “not accurate”.

4. Take a small explant, such as a shoot tip, from the parent. [1] Sterilise it (for example with dilute bleach) and use aseptic technique. [1] Place it on sterile agar containing sugar, minerals and vitamins. [1] Add plant growth regulators; cytokinin and auxin in the right ratio give shoots and roots, and a callus may form first. [1] Divide the shoots and sub-culture to multiply the numbers. [1] Root the plantlets, transfer to compost and acclimatise them gradually. [1] [6] Examiner insight: A strong answer keeps the steps in order and gives at least one condition for sterility and one for the medium.

5. (a) 15 weeks is 5 cycles. [1] 4⁵ = 1024 shoots. [1] (b) 4⁷ = 16 384, which is less than 20 000, and 4⁸ = 65 536. [1] 8 cycles × 3 = 24 weeks. [1] [4] Examiner insight: State the number of cycles before giving weeks, so that the method is visible even if the arithmetic slips.

6. For: many identical plants quickly from one parent. [1] Plants can be produced all year in little space. [1] Meristem culture can give disease-free stock. [1] Against: costly, with skilled staff and sterile facilities. [1] Clones are genetically uniform, so one disease could destroy all plants; plantlets may be lost on transfer to soil. [1] Judgement: worthwhile for a valuable variety sold in large numbers, but less so for a cheap plant that grows well from cuttings. [1] [6] Examiner insight: An evaluation needs a conclusion linked to the context. Listing points on both sides without a decision is usually incomplete.

7. After fertilisation, the zygote divides by mitosis to form a small group of cells. [1] The early embryo splits into two groups, each of which develops into an individual with the same genome as it came from one zygote. [1] Phenotype can differ because of different environments such as diet or disease. [1] Mutations after the split may also differ. [1] [4] Examiner insight: Say that the twins come from one fertilised egg, and link the differences to the environment rather than to “different genes”.

8. (a) Eggs and sperm from chosen cattle are used for in vitro fertilisation. [1] The embryo is allowed to divide to an early stage when its cells are totipotent. [1] The embryo is split into separate groups of cells, which are cultured. [1] The embryos are implanted into surrogate cows. [1] (b) The calves came from one zygote by mitosis, so they have the same genotype. [1] The zygote was produced by a sexual cross with new combinations of alleles, so it is not identical to either parent. [1] [6] Examiner insight: Linking the lack of identity with the parents to meiosis and fertilisation is usually the clearest way of showing understanding.

9. (a) Take a somatic cell from the cow to be cloned. [1] Remove the nucleus from an unfertilised egg (enucleation). [1] Fuse the somatic cell with the egg, using a small electric pulse, or inject its nucleus. [1] Stimulate the egg to divide and culture it to an early embryo. [1] Implant the embryo into a surrogate cow. [1] (b) The nuclear DNA matches the somatic cell donor. [1] Mitochondrial DNA comes from the cytoplasm of the egg donor, so this part of the genome differs. [1] [7] Examiner insight: Keep the roles separate: somatic cell donor, egg donor and surrogate. Mixing them up is an easy way to lose credit.

10. (a) 80 ÷ 200 × 100 = 40%. [1] (b) 16 ÷ 80 × 100 = 20%. [1] (c) 4 ÷ 6 × 100 = 66.7%. [1] (d) Only 4 ÷ 200 = 2% of reconstructed eggs produced a surviving animal, so the method is inefficient and costly. [1] Most pregnancies and births did not give a surviving animal (16 pregnancies, 4 survivors), which raises animal welfare concerns. [1] [5] Examiner insight: Show the division you used. Use the numbers from the question in the concern, not just a general statement.

11. Agriculture, for: copy animals with high yield or good disease resistance, giving a uniform herd. [1] Medicine, for: animals can produce human proteins in milk, and can be used as disease models. [1] Against: reduced genetic diversity, so one disease could affect all the clones. [1] Against: low success and many failed pregnancies raise welfare and ethical concerns. [1] Against: cost is high. [1] Longevity: Dolly was euthanised at about six and a half with lung disease and arthritis, and short telomeres were reported. [1] Later cloned sheep aged 7 to 9 were reported as ageing normally, so the evidence is conflicting and limited. [1] Judgement based on the balance of benefit and harm, with a reason. [1] [8] Examiner insight: Include evidence for the longevity point, and say why it is not conclusive. A one-sided list leaves the evaluation unfinished.

Where marks are usually lost

• Saying a clone from SCNT is identical to the egg donor or the surrogate.
• Giving steps for cuttings or micropropagation without a reason for each.
• Leaving out sterility, or the role of auxin and cytokinin, in tissue culture.
• Using “identical” without saying that the environment can still change phenotype.
• Describing artificial embryo twinning as copying an adult animal.
• Giving percentages without showing the division or the units.
• Evaluating with a one-sided list and no judgement.
• Writing about longevity with no evidence, or treating the evidence as settled.

Next steps

• Revise with the revision notes and the study guide.
• Open the OCR A Level Biology hub and the printable checklist.
• Try all the free 10-minute diagnostics at /diagnostics/.
• Book a free trial class.

Official syllabus

OCR Advanced GCE in Biology A (H420), Version 4.1 (April 2026), first assessment 2025, published by OCR. Section 6.2.1(a) to (d) is covered here.