WJEC A Level Biology
WJEC A Level Biology Unit 4: Variation, Inheritance and Options Exam Questions
Free WJEC A Level Biology exam questions for Unit 4: Variation, Inheritance and Options, with a mark scheme for every pack. Covers Human and plant reproduction, genetic crosses and chi-squared, variation, evolution and speciation, gene technology, and the chosen option.
Unit 4: Variation, Inheritance and Options exam questions
8 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About WJEC A Level Biology Unit 4: Variation, Inheritance and Options
Unit 4 of WJEC A Level Biology, Variation, Inheritance and Options, is the second A2 unit. It covers sexual reproduction in humans and flowering plants, inheritance including dihybrid crosses and sex linkage, variation, natural selection and speciation, and applications such as PCR, genetic engineering and genome projects. It also includes one option taught by your centre: Immunology and Disease, Human Musculoskeletal Anatomy, or Neurobiology and Behaviour. It builds on nucleic acids and meiosis from Unit 1. Examiners regularly set genetic diagrams with chi-squared, Hardy-Weinberg calculations, hormone control of reproduction and evaluation of genetic technologies.
What you need to know
- 4.1 Structure of the testis and ovary, gametogenesis, hormonal control of the menstrual cycle, fertilisation, implantation and the role of the placenta.
- 4.2 Flower structure, pollination and its adaptations, double fertilisation, seed and fruit development, and germination with the role of gibberellin.
- 4.3 Monohybrid and dihybrid inheritance, codominance, sex linkage, autosomal linkage and the chi-squared test, and how mutations arise.
- 4.4 Continuous and discontinuous variation, natural selection, the Hardy-Weinberg principle, genetic drift, and allopatric and sympatric speciation.
- 4.5 PCR, genetic fingerprinting, genetic engineering, gene therapy, genome sequencing and the ethical, social and economic issues they raise.
- Options One option: Immunology and Disease (pathogens, immunity, vaccines, antibiotics), Human Musculoskeletal Anatomy (skeleton, joints, muscle contraction), or Neurobiology and Behaviour (brain structure, learning and behaviour).
Common mistakes in Unit 4: Variation, Inheritance and Options
- Writing gametes with two alleles of the same gene. Each gamete carries one allele of each gene, for example AB, Ab, aB and ab from an AaBb parent.
- Using the wrong number of degrees of freedom for a dihybrid chi-squared test. With four phenotype classes there are 3 degrees of freedom.
- Saying females can be carriers but males cannot inherit X-linked conditions. Males have one X chromosome, so a single recessive allele on it is expressed.
- Treating sympatric speciation as needing a physical barrier. Sympatric speciation occurs in the same area, for example through behavioural isolation or polyploidy.
- Saying gibberellin is the enzyme that breaks down starch in seeds. Gibberellin stimulates the aleurone layer to synthesise amylase, which hydrolyses starch.
Try three Unit 4: Variation, Inheritance and Options exam-style questions
1. A dihybrid cross produced 96, 28, 26 and 10 offspring in four phenotype classes, with an expected 9:3:3:1 ratio. Calculate chi-squared. (3 marks)
Show the mark scheme answer
Total = 160 so expected = 90, 30, 30, 10; (36/90) + (4/30) + (16/30) + (0/10); = 0.40 + 0.13 + 0.53 + 0 = 1.07.
2. Using your answer above, state the conclusion given a critical value of 7.82 at p = 0.05. (2 marks)
Show the mark scheme answer
1.07 is less than 7.82; no significant difference between observed and expected, so the difference is due to chance and the 9:3:3:1 ratio is supported.
3. Describe the functions of the placenta. (3 marks)
Show the mark scheme answer
Exchange of oxygen, carbon dioxide, nutrients and wastes between maternal and fetal blood without mixing; secretes hormones such as progesterone and oestrogen; passes antibodies to the fetus; acts as a barrier to some pathogens.
Unit 4: Variation, Inheritance and Options FAQs
What does WJEC A Level Biology Unit 4: Variation, Inheritance and Options cover?
Sexual reproduction in humans and plants, inheritance, variation and evolution, applications of reproduction and genetics, and one option.
Which option do I need to revise for Unit 4?
Only the option your centre has taught: Immunology and Disease, Human Musculoskeletal Anatomy, or Neurobiology and Behaviour.
How do I set out genetic crosses for full marks?
Write the parental phenotypes and genotypes, list the gametes, use a Punnett square, then give offspring genotypes, phenotypes and the ratio, with a key for the alleles.
