IB DP Biology: Reproduction: sexual and asexual, human reproductive systems and flowering plants (DP Biology) – 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 – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

These questions cover statements D3.1.1 to D3.1.12 of the IB Biology guide, first assessment 2025, for DP Biology. All questions are SL and HL. Data is supplied for practice only.

Use the study guide and revision notes first if needed. See also the IB DP Biology hub, the printable checklist and the free 10-minute diagnostics.

Questions

1. Distinguish between sexual and asexual reproduction, giving one advantage of each. [4]

2. Explain the roles of meiosis and fusion of gametes in a sexual life cycle. [3]

3. A drawing of a human egg cell has a diameter of 84 mm. The actual diameter is 120 µm.

(a) Calculate the magnification of the drawing. [2] (b) Explain why a sperm cell is smaller than an egg cell and why far more sperm than eggs are produced. [3]

4. State the function of each of these male structures: (a) scrotum, (b) epididymis, (c) seminal vesicle. [3]

5. The table shows hormone concentrations in one menstrual cycle, in arbitrary units.

Day	4	8	12	13	14	18	22	26
Oestradiol	40	90	260	220	90	160	170	50
LH	6	7	10	48	20	6	5	5
Progesterone	1	1	2	4	6	14	16	3

(a) Suggest the day on which ovulation most likely happened. [1] (b) Calculate the percentage increase in LH between day 12 and day 13. [2] (c) Explain the rise in LH between day 12 and day 13. [2] (d) State the source of the progesterone on day 22 and one role it has. [2] (e) Explain the changes in the hormones between day 22 and day 26 and the effect on the endometrium. [2]

6. Describe the events of fertilization in humans that follow fusion of the sperm and egg cell membranes. [5]

7. In an IVF cycle, 14 eggs were collected and 10 were fertilized.

(a) Outline how hormones are used before the eggs are collected. [3] (b) Calculate the percentage of eggs that were fertilized, to 3 significant figures. [2] (c) Suggest one risk of using hormones in this way. [1]

8. Describe the sequence of events in a flowering plant from pollination to formation of an embryo, and explain why a hermaphrodite flower still shows sexual reproduction. [6]

9. Describe four features of an insect-pollinated flower, linking each feature to its function. [4]

10. Cross-pollination is promoted in many species.

(a) Outline three methods of promoting cross-pollination. [3] (b) Explain why inbreeding is a disadvantage to a plant population. [2] (c) A stigma belongs to a plant with self-incompatibility alleles S2 and S3. Pollen from donor A (alleles S1 and S2) and donor B (alleles S1 and S4) lands on the stigma. State the percentage of pollen from each donor that can grow, and explain. [3]

11. The table shows the dry mass of a single germinating seed.

Day	0	2	4	6	8	10	12
Dry mass (mg)	52	49	44	38	36	40	52

(a) Describe the change in dry mass from day 0 to day 12. [2] (b) Explain the change from day 0 to day 8. [3] (c) Calculate the percentage change in dry mass from day 0 to day 8. [2] (d) Explain the change after day 8. [2] (e) Distinguish between seed dispersal and pollination. [2]

12. A grower has a strawberry variety that is well suited to the farm and propagates it with runners.

(a) State why runners produce plants that are genetically identical to the parent. [1] (b) Suggest one advantage and one disadvantage of this method if a new fungal disease arrives. [2] (c) Explain why a plant breeder who wants disease-resistant plants grows strawberries from seed. [3]

Answers

1. Asexual reproduction involves one parent and no gametes, giving genetically identical offspring [1]. Sexual reproduction involves fusion of two gametes made by meiosis, giving varied offspring [1]. Asexual advantage: offspring keep a genotype that suits the present environment, and reproduction is fast [1]. Sexual advantage: new gene combinations, so some offspring may be adapted to a changed environment [1]. [4] Examiner insight: “Distinguish” needs a difference stated for both sides; naming only one process loses the comparison, and an advantage must be linked to environment or variation, not just “better”.

2. Meiosis halves the chromosome number to produce haploid gametes [1]. It breaks up parental combinations of alleles, so gametes differ [1]. Fusion of gametes restores the diploid number and creates a new combination of alleles in the zygote [1]. [3] Examiner insight: Say what each process does to the chromosome number and to allele combinations.

3. (a) Convert 84 mm to 84 000 µm [1]. Magnification = 84 000 ÷ 120 = ×700 [1]. [2] (b) The sperm swims to the egg, so a small, light cell with little food reserve is enough [1]. The egg does not travel and needs food reserves for the early embryo, so it is larger [1]. Many sperm are made because few reach the egg, while few eggs are made because each is large and costly to produce [1]. [3] Examiner insight: A magnification answer needs the units converted before dividing; a correct method with mixed units gives a number that is a thousand times out.

4. (a) The scrotum keeps the testes outside the abdomen at a temperature a little below body temperature [1]. (b) The epididymis stores sperm while they mature [1]. (c) The seminal vesicle adds fluid that nourishes the sperm and helps carry them [1]. [3] Examiner insight: Give a function, not just a position; “next to the testis” does not describe what the structure does.

5. (a) Day 14 (just after the LH peak on day 13) [1]. [1] (b) Increase = 48 − 10 = 38 [1]. Percentage = 38 ÷ 10 × 100 = 380% [1]. [2] (c) Oestradiol from the growing follicle is high, at 260 units on day 12 [1]. High oestradiol over time acts by positive feedback on the pituitary, causing an LH surge [1]. [2] (d) The corpus luteum (the remains of the follicle) secretes it [1]. It maintains the thick endometrium (or inhibits FSH and LH) [1]. [2] (e) The corpus luteum breaks down, so progesterone falls from 16 to 3 and oestradiol falls from 170 to 50 [1]. With no hormone support the endometrium is shed in menstruation [1]. [2] Examiner insight: Quote both the hormone and the data values when you explain a graph or table. State the type of feedback by name, because “hormone rises” alone does not explain the surge.

6. The sperm nucleus enters the egg [1]. The sperm tail and mitochondria are destroyed, so they are not passed on [1]. The nuclear membranes of both nuclei dissolve [1]. All the condensed chromosomes, 23 from each parent, take part in a joint mitosis [1]. This gives two diploid nuclei, each with 46 chromosomes [1]. [5] Examiner insight: Put the events in order and note that mitosis, not meiosis, follows; “the nuclei fuse” alone misses the dissolution of the membranes.

7. (a) Natural hormone secretion is suspended with drugs [1]. Injections of FSH (with LH) are given in artificial doses [1]. This induces superovulation, so many follicles mature at once [1]. [3] (b) 10 ÷ 14 × 100 = 71.43 [1], so 71.4% [1]. [2] (c) Over-stimulation of the ovaries, or a multiple pregnancy if several embryos are transferred [1]. [1] Examiner insight: Mention both parts of the idea: normal secretion stopped, then artificial doses given. The final answer should be given to the number of significant figures the question asks for.

8. Pollen is transferred from an anther to a stigma [1]. The pollen grain germinates and a pollen tube grows down the style [1]. The tube carries the male gamete to the ovule [1]. A male gamete fuses with the egg cell to make a zygote [1]. The zygote divides by mitosis to form an embryo [1]. Even a hermaphrodite flower makes gametes by meiosis, and these fuse, so it is sexual reproduction [1]. [6] Examiner insight: Keep pollination, pollen tube growth and fertilization as separate stages; answers that merge them lose marks even when all the words are present.

9. Any four, each feature with its function: large coloured petals attract insects [1]; nectar in nectaries rewards insects [1]; anthers on filaments where an insect touches them [1]; sticky or spiny pollen clings to the insect [1]; sticky stigma that brushes the insect and catches pollen. [4] Examiner insight: Each mark needs a feature and its function together. Listing parts without functions is a common way to lose marks on an annotation task.

10. (a) Different maturation times for anthers and stigma [1]. Separate male and female flowers, or separate male and female plants [1]. Animals or wind carry pollen between plants [1]. [3] (b) Inbreeding lowers genetic diversity, so the population cannot adapt as well to change [1]. It also reduces vigour (fitness) of offspring [1]. [2] (c) Donor A: S2 pollen is blocked because it matches the stigma, S1 pollen can grow, so 50% [1]. Donor B: neither S1 nor S4 matches S2 or S3, so 100% can grow [1]. The match to an allele in the plant’s own tissue blocks the pollen, so only pollen from other plants succeeds [1]. [3] Examiner insight: In genetic crosses of this kind, show which allele is blocked and which is not; a bare percentage is hard to credit if the reasoning is missing.

11. (a) Dry mass falls from 52 mg to 36 mg by day 8 [1], then rises back to 52 mg by day 12 [1]. [2] (b) The seed takes in water, and the embryo releases gibberellin [1]. This triggers production of amylase, which digests stored starch to sugars [1]. The sugars are used in respiration and lost as carbon dioxide, so dry mass falls [1]. [3] (c) (36 − 52) ÷ 52 × 100 [1] = −30.8% [1]. [2] (d) The seedling has leaves that photosynthesise [1]. It now makes more organic matter than it uses in respiration, so dry mass increases [1]. [2] (e) Dispersal moves seeds away from the parent plant [1]. Pollination is the transfer of pollen from anther to stigma [1]. [2] Examiner insight: A percentage change must carry its sign. In an explanation question, name the process (respiration, photosynthesis) and the molecule involved rather than writing that the seed “uses energy”.

12. (a) Runners grow by mitosis from the parent, so they carry the same genes [1]. [1] (b) Advantage: the plants stay well suited to the farm and are quick to produce [1]. Disadvantage: all plants are identical, so a disease that can infect one can infect all [1]. [2] (c) Sexual reproduction by seed uses meiosis and fusion of gametes [1]. This gives new combinations of alleles, so some seedlings may carry resistance [1]. Those can be selected and then grown on [1]. [3] Examiner insight: For a “suggest” question, tie the idea to the situation named, here the disease.

Where marks are usually lost

• Mixing up pollination, fertilization and dispersal.
• Not naming the hormone, or not naming the type of feedback.
• Forgetting to convert units in magnification.
• Omitting the sign on a percentage decrease.
• Writing that gametes are made by mitosis.
• Saying a hermaphrodite plant reproduces asexually.
• Giving a flower part without its function.
• Describing IVF as only “mixing eggs and sperm” without the use of hormones.

Next steps

• Re-read the revision notes and the study guide.
• Tick off statements on the printable checklist and open the IB DP Biology hub.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

IB Biology guide, first assessment 2025, published by the International Baccalaureate Organization, statements D3.1.1 to D3.1.12.