Cambridge O Level Biology 5090: Development of organisms and continuity of life (5090) – 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 Topic 16, Development of organisms and continuity of life, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4): every section from 16.1 Nuclear division to 16.4 Sexual reproduction in humans. The syllabus is not tiered, so every question applies to every candidate.

Revise first with the study guide and the revision notes. The course hub and the printable checklist list the other topics, and the free 10-minute diagnostics help you decide what to revise next. A calculator is useful for question 8. All data are given values for the question, not reference figures to learn.

Questions

1. (a) Describe a haploid nucleus and a diploid nucleus. [2] (b) State how many pairs of chromosomes are in a human diploid cell. [1]

2. A plant species has a diploid number of 26.

(a) State the number of chromosomes in a male gamete nucleus of this plant. [1] (b) State the number of chromosomes in the zygote formed at fertilisation. [1] (c) The zygote divides to form an embryo. Name the type of division and state the chromosome number in each embryo cell. [2]

3. (a) Outline two roles of mitosis in a human. [2] (b) Describe what is meant by a stem cell. [2] (c) Explain how a cancer forms. [1] (d) Describe meiosis. [1]

4. A farmer grows potatoes from tubers taken from one high-yielding plant.

(a) Describe asexual reproduction. [2] (b) Discuss one advantage and one disadvantage to the farmer of growing the crop in this way. [4]

5. (a) State the function of the sepals, the anther and the stigma. [3] (b) State two ways in which the pollen of an insect-pollinated flower differs from the pollen of a wind-pollinated flower. [2]

6. A plant species can self-pollinate or cross-pollinate.

(a) Distinguish between self-pollination and cross-pollination. [2] (b) In one area the numbers of insect pollinators fall sharply and summers become hotter. Discuss how relying on self-pollination would affect a population of this plant. [3]

7. Describe what happens between a pollen grain landing on a stigma and the formation of a seed and a fruit. [5]

8. A student placed 50 seeds on damp cotton wool in air at each of five temperatures and counted the seeds that had germinated after six days.

Temperature / °C	5	15	25	35	45
Seeds germinated	4	21	46	38	0

(a) Calculate the percentage germination at 15 °C and at 25 °C. [2] (b) Describe the effect of temperature on germination shown by these results. [2] (c) Suggest why no seeds germinated at 45 °C. [2] (d) Describe the role of water and enzymes in germination. [3]

9. (a) State the function of the testa, the plumule and the cotyledons. [3] (b) A fruit has two thin wings. Explain how this feature helps dispersal. [2] (c) Explain why seed dispersal benefits a plant species. [2]

10. (a) State the function of the prostate gland, the oviduct and the cervix. [3] (b) Explain how the flagellum, the mitochondria and the acrosome help a sperm cell to carry out its function. [3] (c) Explain how two features of an egg cell are related to its function. [2] (d) Compare male and female gametes in terms of numbers and motility. [2]

11. (a) State one secondary sexual characteristic controlled by testosterone and one controlled by oestrogen. [2] (b) Explain the roles of FSH and LH in the menstrual cycle. [3] (c) Explain the roles of oestrogen and progesterone in controlling the lining of the uterus. [4]

12. (a) Describe the early development of a zygote up to implantation. [2] (b) State the function of the amniotic fluid. [1] (c) Describe the functions of the placenta and the umbilical cord. [4] (d) A pregnant woman is infected with a virus. State why this may be a risk to the fetus. [1]

Answers

1. (a) Haploid: a single set of chromosomes [1]. Diploid: two sets of chromosomes (a pair of each type) [1]. (b) 23 pairs [1]. Examiner insight: “Half the chromosomes” is weaker than “a single set”; use the syllabus wording so the description cannot be misread.

2. (a) 26 ÷ 2 = 13 [1]. (b) 13 + 13 = 26 [1]. (c) Mitosis [1]; 26 [1]. Examiner insight: In (c) the type of division and the number are separate answers, so a correct number with “meiosis” still loses the first mark.

3. (a) Any two: growth; repair of damaged tissues; replacement of dying cells; asexual reproduction [2]. (b) An unspecialised cell [1] that divides by mitosis to give daughter cells that can become specialised [1]. (c) Uncontrolled cell division [1]. (d) A reduction division that halves the chromosome number (diploid to haploid), giving genetically different cells / gametes [1]. Examiner insight: For (b), “unspecialised” alone describes the cell but not what it does; add that its daughter cells specialise.

4. (a) Offspring produced from one parent [1] that are genetically identical [1]. (b) Advantage: all plants are genetically identical to the parent [1], so they all keep its high yield [1]. Disadvantage: there is no variation [1], so a new disease or change in conditions could damage the whole crop [1]. Examiner insight: “Discuss” needs a reason with each point; “no variation” without saying why that matters gives only half the credit available.

5. (a) Sepals protect the flower in bud [1]; anther makes (and releases) pollen [1]; stigma receives pollen [1]. (b) Any two, stated as comparisons: insect pollen is larger; sticky or spiky rather than smooth; made in smaller amounts [2]. Examiner insight: Make each difference a comparison (“larger than”, “spiky, not smooth”); a feature of one type only is often not credited.

6. (a) Self: pollen goes to a stigma of the same flower or the same plant [1]. Cross: pollen goes to a stigma on a different plant of the same species [1]. (b) Seeds can still form without insect pollinators [1]. But there is less variation [1], so the population is less able to respond to the hotter summers [1]. Examiner insight: Cover both sides of a “discuss”: the pollinator point is an advantage, the variation point a disadvantage.

7. A pollen tube grows from the pollen grain [1] down through the style to the ovary [1]. It enters the ovule (through the micropyle) [1]. The male nucleus fuses with the female nucleus (fertilisation) [1]. The ovule becomes the seed and the ovary becomes the fruit [1]. Examiner insight: Use the term “nucleus” for what fuses; “the pollen fuses with the ovule” describes the wrong structures.

8. (a) 21 ÷ 50 × 100 = 42% [1]; 46 ÷ 50 × 100 = 92% [1]. (b) Germination increases as temperature rises from 5 °C to 25 °C [1], then falls at 35 °C and is zero at 45 °C [1]. (c) Enzymes in the seed are denatured [1], so stored food cannot be broken down for respiration and growth [1]. (d) Water is absorbed and activates enzymes [1]. Enzymes such as amylase break down stored starch to maltose (or proteases break proteins to amino acids) [1]. Soluble products move to the embryo and are used in respiration and growth [1]. Examiner insight: In (b), quote the temperatures from the table; a trend described with no data is less likely to get both marks.

9. (a) Testa protects the embryo [1]; plumule becomes the shoot [1]; cotyledons store food [1]. (b) Wings increase surface area / slow the fall [1], so the wind carries the fruit further from the parent [1]. (c) Plants colonise new areas [1] and there is less competition with the parent (and each other) for light, water and mineral ions [1]. Examiner insight: For (c), name what the plants compete for; “less competition” with no resource named is vague.

10. (a) Prostate gland adds fluid to sperm to form semen [1]; oviduct carries the egg to the uterus / is where fertilisation happens [1]; cervix is a ring of muscle at the base of the uterus that widens at birth [1]. (b) Flagellum lashes so the sperm swims to the egg [1]; mitochondria release energy (by respiration) for swimming [1]; acrosome enzymes digest a way through the jelly coat [1]. (c) Energy stores supply the early embryo [1]; the jelly coat changes at fertilisation so no other sperm can enter [1]. (d) Sperm are made in far greater numbers than eggs [1]; sperm swim but eggs cannot [1]. Examiner insight: In (b), say mitochondria “release energy”; writing that they “make energy” is a common reason for losing the mark.

11. (a) Testosterone: any one of facial or body hair, deeper voice, muscle growth [1]. Oestrogen: any one of breast development, wider hips, start of the menstrual cycle [1]. (b) FSH (from the pituitary) causes an egg to develop in the ovary [1] and stimulates oestrogen production [1]. LH causes ovulation [1]. (c) Oestrogen makes the uterus lining thicken (rebuild) [1]. Progesterone keeps the lining thick [1]. If there is no pregnancy, progesterone level falls [1] and the lining breaks down (menstruation) [1]. Examiner insight: Keep each hormone with its own effect; swapping FSH and LH, or giving ovulation to oestrogen, loses the linked marks.

12. (a) The zygote divides by mitosis to form a ball of cells (embryo) [1], which implants in the lining of the uterus [1]. (b) Protects the fetus from knocks / supports it [1]. (c) Placenta: oxygen and dissolved nutrients pass from mother’s blood to fetus’s blood [1]; carbon dioxide and urea pass from fetus to mother [1]; the two bloods do not mix [1]. Umbilical cord carries the fetus’s blood to and from the placenta [1]. (d) Some viruses can cross the placenta and affect the fetus [1]. Examiner insight: Give direction for each substance in (c); “exchanges gases and food” without saying which way scores less.

Where marks are usually lost

• Writing that mitosis halves the chromosome number, or that meiosis gives identical cells.
• Giving “46 pairs” instead of 23 pairs for a human diploid cell.
• Saying pollen lands on “the flower” or “the ovary” instead of the stigma.
• Describing self-pollination as pollen from “the same species” (cross-pollination is also within one species).
• Describing a trend without quoting data from the table.
• Saying water “gives energy” to a germinating seed.
• Saying the acrosome digests “the egg” rather than the jelly coat.
• Mixing up which hormone causes ovulation (LH) and which keeps the lining thick (progesterone).
• Saying maternal and fetal blood mix at the placenta.

Next steps

• Go back over weak points with the revision notes and the study guide.
• Link germination back to Enzymes and the placenta to Disease and immunity.
• See every topic on the course hub and tick off outcomes on the printable checklist.
• Try the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4), Topic 16: Development of organisms and continuity of life (16.1 Nuclear division; 16.2 Asexual and sexual reproduction; 16.3 Sexual reproduction in plants; 16.4 Sexual reproduction in humans), published by Cambridge Assessment International Education.