Pearson Edexcel IGCSE Biology: Reproduction and Inheritance — Practice Questions (4BI1)

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — Pearson holds copyright in its own papers. Use these alongside the official past papers available through your school or Pearson’s own resources.

Related: Topic 3 study guide and revision notes.

Section A

1. Define “genome.” [1]

2. State the human diploid and haploid chromosome numbers. [2]

3. Name the two structures whose roles are: nourishing the developing embryo, and protecting it. [2]

Section B

4. In pea plants, tall (T) is dominant over short (t). Two heterozygous tall plants (Tt) are crossed.

(a) Draw a full genetic diagram showing the parents’ genotypes, gametes, and offspring genotypes. [3] (b) State the phenotype ratio of the offspring. [1] (c) Explain why most phenotypic features are not inherited this simply. [2]

5. A cell undergoes mitosis, and a different cell of the same organism undergoes meiosis.

(a) State how many daughter cells result from each process. [2] (b) Explain why the cells resulting from meiosis are genetically different from each other, while those from mitosis are genetically identical. [3]

6. A student sets up four test tubes to investigate the conditions needed for seed germination: Tube A (water + air + warmth), Tube B (no water + air + warmth), Tube C (water + no air, sealed with oil + warmth), Tube D (water + air + refrigerated). Only Tube A shows germination after one week.

(a) Explain why Tube B did not germinate. [1] (b) Explain why Tube C did not germinate. [2] (c) Suggest why Tube D did not germinate. [1]

Section C

7. A population of bacteria is exposed to an antibiotic. Most bacteria die, but a small number survive and reproduce, and the resulting population shows increased antibiotic resistance.

(a) Explain, using Darwin’s theory of natural selection, how this resistant population arose. [4] (b) Explain why this process is described as “natural selection” rather than the antibiotic directly causing bacteria to become resistant. [3]

Worked answers

1. An organism’s entire DNA. [1]

2. Diploid = 46, haploid = 23. [2]

3. The placenta nourishes the developing embryo; amniotic fluid protects it. [2]

4. (a) Parents: Tt x Tt. Gametes: T, t (from each parent). Offspring: TT, Tt, Tt, tt. [3] (1 mark for correct parental genotypes and gametes, 2 for correctly combined offspring genotypes.) (b) 3 tall : 1 short. [1] (c) Most phenotypic features arise from polygenic inheritance (many genes acting together), not a single gene as in this simplified monohybrid example, so a real trait’s inheritance pattern is usually far more complex than a single dominant/recessive pair predicts. [2]

5. (a) Mitosis produces 2 daughter cells; meiosis produces 4 daughter cells. [2] (b) Meiosis involves genetic mixing (independent assortment and the halving of chromosome number from diploid to haploid), producing four genetically different haploid gametes; mitosis simply copies the parent cell’s genetic material exactly and divides it between two daughter cells, so no genetic mixing occurs and the resulting cells are genetically identical to the parent cell and each other. [3]

6. (a) Tube B had no water, and water is a required condition for germination. [1] (b) Tube C was sealed with oil, preventing oxygen from reaching the seed; oxygen is required for respiration, which provides the energy needed for germination, so without it germination cannot proceed. [2] (c) The refrigerated temperature was likely too low for the enzymes controlling germination to work at a sufficient rate, since enzyme activity (and therefore metabolic processes like germination) slows significantly at low temperatures. [1]

7. (a) Within the original bacterial population, natural genetic variation meant a small number of bacteria already happened to carry resistance to the antibiotic before exposure; when the antibiotic was applied, non-resistant bacteria were killed while the resistant few survived and reproduced, passing the resistance allele on to their offspring, so the surviving population’s proportion of resistant bacteria increased over subsequent generations. [4] (Marks for correctly stating pre-existing variation, differential survival, and inheritance of the trait by offspring.) (b) The antibiotic did not cause any bacteria to become resistant – it acted as a selection pressure that killed non-resistant bacteria, allowing already-resistant individuals (who existed before exposure due to natural variation) to survive and reproduce disproportionately; this distinction (selecting existing variation vs causing new variation) is the core of natural selection as Darwin described it, and confusing the two is a very common misconception. [3]

8. State the base-pairing rule in DNA, and name the base found in RNA in place of thymine. [2]

Worked answers (continued)

8. Adenine pairs with thymine, and cytosine pairs with guanine. RNA uses uracil in place of thymine – this base-pairing rule is what allows DNA to be copied accurately and is the same rule protein synthesis relies on when messenger RNA is built from a DNA template. [2]

Why question 7 targets a common misconception directly

Question 7(b) is deliberately written to test the distinction between an environmental pressure selecting existing genetic variation and an environmental pressure causing that variation to appear, because this is one of the most persistent misconceptions in natural selection questions at this level – a student who believes the antibiotic itself made bacteria resistant has fundamentally misunderstood the mechanism, even if they can correctly describe the population-level outcome.

Official syllabus

Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3 (September 2024) – official specification PDF – the same source cited by the study guide and revision notes.