Edexcel International GCSE Biology Section 3: Reproduction and Inheritance Exam Questions

About Edexcel International GCSE Biology Section 3: Reproduction and Inheritance

Section 3 of Edexcel International GCSE Biology is examined across Paper 1 and Paper 2. It covers reproduction in flowering plants and humans, including pollination, fertilisation, germination, the menstrual cycle and the role of the placenta, followed by inheritance: DNA and genes, protein synthesis, monohybrid crosses, family pedigrees, mitosis and meiosis, variation, mutation and evolution by natural selection. It links to hormones in Section 2 and to genetic modification in Section 5. Examiners frequently set genetic diagrams with ratios and probabilities, compare insect and wind pollinated flowers, and ask about the conditions needed for germination.

What you need to know

• Sexual and asexual reproduction Sexual reproduction involves fusion of haploid gametes to form a diploid zygote, giving variation. Asexual reproduction produces genetically identical offspring, for example plant runners and cuttings.
• Flowering plants Insect pollinated flowers have large, brightly coloured petals, scent and nectar; wind pollinated flowers have small petals, large feathery stigmas and anthers hanging outside. After pollination a pollen tube grows to the ovule, fertilisation occurs and a seed and fruit form. Germination needs water, oxygen and a suitable temperature.
• Human reproduction Know the male and female reproductive systems. Oestrogen and progesterone control the menstrual cycle; FSH stimulates follicle development and LH stimulates ovulation. The placenta exchanges oxygen, nutrients and waste between mother and fetus, and amniotic fluid protects the developing embryo. Testosterone and oestrogen control secondary sexual characteristics.
• DNA and protein synthesis DNA is a double helix of two strands with complementary bases A with T and C with G. A gene is a section of DNA that codes for a protein. In transcription mRNA is made in the nucleus; in translation, tRNA brings amino acids to the ribosome, and each base triplet codes for one amino acid.
• Inheritance Learn allele, dominant, recessive, homozygous, heterozygous, genotype, phenotype and codominance. Use genetic diagrams for monohybrid crosses and interpret family pedigrees. Sex is determined by XX (female) and XY (male) chromosomes.
• Cell division Mitosis produces two genetically identical diploid cells for growth, repair, cloning and asexual reproduction. Meiosis produces four genetically different haploid gametes. Human body cells have 46 chromosomes (diploid) and gametes 23 (haploid).
• Variation and evolution Variation is genetic, environmental or both. Mutation is a rare random change in genes or chromosomes; ionising radiation and some chemicals increase the rate. Natural selection acts on variation, and antibiotic resistance in bacteria shows evolution by natural selection.

Common mistakes in Section 3: Reproduction and Inheritance

• Saying pollination and fertilisation are the same. Pollination is the transfer of pollen; fertilisation is the fusion of the male and female nuclei in the ovule.
• Saying light is needed for germination. Seeds need water, oxygen and a suitable temperature; light is not required for germination itself.
• Saying the mother's blood mixes with the fetus's blood. Substances diffuse across the placenta; the bloods do not mix.
• Writing genetic diagrams without gametes. Show the parental genotypes, the gametes and the offspring genotypes and phenotypes.
• Saying mutations are always harmful. Most have no effect, and a few can be beneficial.

Try three Section 3: Reproduction and Inheritance exam-style questions