CIE iGCSE Co-Ordinated Science B15.2 Sexual reproduction Exam Style Questions Paper 4
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B15.1 — Asexual reproduction (Part a(i))
• Topic B15.2 — Sexual reproduction (Part a(ii))
• Topic B15.3 — Sexual reproduction in plants (Parts b(i) & b(ii))
• Topic B16.2 — Cell division (Parts c(i) & c(ii))
▶️ Answer/Explanation
(a)(i) Advantages of asexual reproduction in violet plants:
1. Faster reproduction — asexual reproduction allows rapid production of many offspring without the need for pollination or fertilisation.
2. Requires only one parent — no need for a mate, pollinators, or production of flowers and scent, saving energy.
3. Genetically identical offspring — if the parent plant has desirable characteristics, these are passed on unchanged (clones).
4. Less energy required — resources are not wasted on producing flowers, nectar, or attracting pollinators.
(a)(ii) Sexual reproduction in plants:
Sexual reproduction is the process involving the fusion of nuclei of two gametes to form the zygote.
(b)(i) Functions of structures in Fig. 3.2:
Structure A (Stigma) — It is the part of the female reproductive organ (carpel) that is adapted to capture pollen grains from the air. In wind-pollinated flowers, it is often feathery or branched to increase the surface area for catching airborne pollen.
Structure B (Anther) — It is part of the male reproductive organ (stamen) that produces pollen grains. Pollen grains contain the male gametes (sperm nuclei).
(b)(ii) Difference in an insect-pollinated flower:
In an insect-pollinated flower, structure B (the anther) would not be hanging down outside the flower. Instead, it would be enclosed within the flower, positioned so that insects brushing against it pick up pollen. Additionally, insect-pollinated flowers typically have large, colourful petals, nectar, and scent to attract insects, unlike wind-pollinated flowers which often lack these features.
(c)(i) Chromosome numbers in violet plants:
Root hair cells contain 30 chromosomes. Root hair cells are diploid (2n) as they are somatic (body) cells.
A leaf cell is also a somatic cell, so it is diploid (2n) and contains 30 chromosomes.
An ovule is a female gamete, which is haploid (n). Therefore, it contains half the diploid number: 15 chromosomes.
(c)(ii) Process leading to formation of gametes:
The process is meiosis — a type of nuclear division that reduces the chromosome number from diploid (2n) to haploid (n), producing genetically different gametes.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B2.1 — Cell structure (Part (a))
• Topic B16.2 — Cell division / Mitosis (Part (b)(i))
• Topic B15.2 — Sexual reproduction (Part (b)(ii))
• Topic B15.3 — Sexual reproduction in plants (Part (c)(i) & (c)(ii))
• Topic B16.2 — Cell division / Meiosis (Part (d))
▶️ Answer/Explanation
(a) Similar:
1. Both have a cell wall surrounding the cell membrane.
2. Both contain ribosomes for protein synthesis and DNA as genetic material.
Both plant and bacterial cells share basic structural features like a cell wall, cell membrane, cytoplasm, and ribosomes.
(a) Different:
1. Plant cell wall is made of cellulose; bacterial cell wall is made of peptidoglycan (sugars and amino acids).
2. Plant cells have chloroplasts and a vacuole; bacterial cells lack these organelles.
Plant cells have membrane-bound organelles like chloroplasts and a nucleus, whereas bacterial cells have circular DNA and plasmids without a nucleus.
(b)(i) chromosomes
DNA replication occurs before mitosis to ensure each daughter cell receives an identical set of chromosomes.
(b)(ii) Advantage: Produces genetic variation in offspring.
Disadvantage: Takes longer than asexual reproduction as offspring develop from fertilised eggs.
Sexual reproduction promotes diversity through gamete fusion, but requires more time and energy compared to asexual methods.
(c)(i) A – stigma ; B – style
The stigma is the receptive surface for pollen grains, and the style is the stalk connecting the stigma to the ovary.
(c)(ii) C: In wind-pollinated flowers, petals are dull/small/absent and have no scent.
D: Anthers are hanging outside the flower to release pollen easily into the wind.
Wind-pollinated flowers lack bright colours and nectar, and their anthers are exposed for efficient pollen dispersal by air currents.
(d) meiosis
Meiosis is the reduction division that produces haploid gametes from diploid cells, halving the chromosome number.