Eduqas A-Level Biology Component 2 Continuity of Life: a deep dive on classification, reproduction, inheritance, evolution and gene technology

What Component 2 actually demands

Continuity of Life is the genetics and evolution paper of Eduqas A-Level Biology. The component runs from how organisms are classified and how related they are, through how humans and plants reproduce, how characteristics are inherited, how populations evolve, and finally how we read, copy and engineer genomes. Examiners test two linked skills: precise recall of processes and definitions, and confident handling of genetic and statistical calculations.

This guide walks through all six topics in a sensible build order, then sets out the exam patterns Eduqas repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Classification and biodiversity

Organisms are classified in a hierarchy (domain to species) and named by the binomial system. The three-domain system (Bacteria, Archaea, Eukarya) is based on molecular evidence, which split the prokaryotes into two domains. Phylogeny is the evolutionary history; modern classification aims to reflect it. A species is a group that can interbreed to produce fertile offspring. Biodiversity is measured by the index of diversity, which combines species richness with evenness; genetic diversity is the variety of alleles in a population.

Sexual reproduction in humans

Gametes form by meiosis: spermatogenesis makes many small motile sperm, oogenesis few large eggs. A sperm has an acrosome, a haploid nucleus, a mitochondria-packed midpiece and a flagellum. At fertilisation, the acrosome reaction digests the egg's layers, the nuclei fuse, and the cortical reaction blocks further sperm. The menstrual cycle is controlled by FSH (follicle and oestrogen), oestrogen (thickens the lining, triggers the LH surge), LH (ovulation) and progesterone (maintains the lining).

Sexual reproduction in plants

A flower's stamen (anther and filament) is male; the carpel (stigma, style and ovary) is female. Gametes form by meiosis in the anther and the ovule. After pollination, a pollen tube grows to the ovule and delivers two male nuclei: in double fertilisation one fuses with the egg (diploid zygote, then embryo) and the other with the two polar nuclei (triploid endosperm). The ovule becomes the seed, the ovary the fruit. Plants promote cross-pollination, for genetic variation, by separating anther and stigma in time or space or by self-incompatibility.

Inheritance

A monohybrid cross of two heterozygotes gives 3:1; a dihybrid cross of two double heterozygotes gives 9:3:3:1. Codominance (both alleles expressed, as in AB blood), multiple alleles (ABO), sex linkage (X-linked recessives commoner in males, with female carriers) and epistasis (one gene affecting another) all modify the patterns. Use defined alleles and a Punnett square. The chi-squared test compares observed with expected results: state a null hypothesis, find degrees of freedom, and compare with the critical value at p equals 0.05.

Variation and evolution

Variation comes from mutation, meiosis and random fertilisation. In natural selection, a selection pressure favours advantageous alleles, so their frequency rises; selection can be directional, stabilising or disruptive. The Hardy-Weinberg principle predicts allele and genotype frequencies in a non-evolving population (p plus q equals 1; p squared plus 2pq plus q squared equals 1), and a measured change is evidence of evolution. Genetic drift changes frequencies by chance, especially in small populations. Speciation follows reproductive isolation and divergence.

Applications of reproduction and genetics

Recombinant DNA technology transfers a gene (isolated by a restriction enzyme or reverse transcriptase) into a plasmid vector with DNA ligase, then into a host, selected with a marker. PCR amplifies DNA in cycles of denaturation, annealing and extension by a heat-stable polymerase, doubling the DNA each cycle. Gel electrophoresis separates fragments by size. DNA profiling and sequencing identify and read DNA; genetic screening tests for disease alleles and raises ethical issues.

How Component 2 is examined

A typical Eduqas profile for Continuity of Life:

• Recall and definitions. The taxonomic hierarchy, gamete structure, the menstrual-cycle hormones, and the steps of gene technology.
• Maths. A genetic cross, a chi-squared test, a Hardy-Weinberg calculation, or an index of diversity.
• Applied and data questions. Reading a DNA profile, interpreting a selection example, or evaluating an ethical issue in genetic screening.
• Levels-of-response QER. Natural selection changing allele frequency, hormonal control of the menstrual cycle, double fertilisation, or making a protein by recombinant DNA technology make predictable extended-response questions.

Check your knowledge

A mix of recall and application questions covering the whole of Component 2. Attempt them under timed conditions, then check against the solutions.

1. State the three domains and the basis on which the three-domain system was established. (2 marks)
2. State two structural adaptations of a sperm cell and their functions. (2 marks)
3. Name the hormone that triggers ovulation and the gland that secretes it. (2 marks)
4. State the products of double fertilisation in a plant and their ploidy. (2 marks)
5. A dihybrid cross AaBb by AaBb gives 320 offspring. Calculate how many are expected to show both recessive traits. (2 marks)
6. In a population, q squared equals 0.09. Calculate the frequency of the dominant allele. (2 marks)
7. State the three temperature steps of one PCR cycle and what happens at each. (3 marks)
8. Explain how natural selection changes the allele frequency of a population over time. (4 marks)