Edexcel A Level Biology A (Salters-Nuffield)
Edexcel A Level Biology A Topic 2: Genes and Health Exam Questions
Free Edexcel A Level Biology A exam questions for Topic 2: Genes and Health, with a mark scheme for every pack. Covers cystic fibrosis, gas exchange surfaces, membrane structure and transport, protein structure, enzymes, DNA, protein synthesis, inheritance and genetic screening.
Topic 2: Genes and Health exam questions
1 question pack 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 Edexcel A Level Biology A Topic 2: Genes and Health
Topic 2 of Edexcel A Level Biology A (Salters-Nuffield) uses cystic fibrosis as the context for learning about gas exchange, membranes, proteins and inheritance. You study the properties of gas exchange surfaces and Fick's law, the fluid mosaic model and transport across membranes, the structure of proteins and how enzymes work. The topic then covers the structure of DNA and RNA, semi-conservative replication, the genetic code, transcription and translation, gene mutations and monohybrid inheritance. You finish by evaluating genetic screening and the ethical issues it raises. Core practicals on membrane permeability using beetroot and the initial rate of enzyme activity are frequently tested.
What you need to know
- Gas exchange and Fick's law Rate of diffusion is proportional to surface area x concentration difference / thickness of the exchange surface. In cystic fibrosis, thick mucus reduces gas exchange and blocks pancreatic ducts.
- Membranes and transport The fluid mosaic model includes phospholipids, proteins, cholesterol and glycoproteins. Transport: diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis. The CFTR protein is a chloride ion channel.
- Proteins and enzymes Amino acids join by peptide bonds. Primary, secondary, tertiary and quaternary structure determine shape; globular proteins are soluble while fibrous proteins have structural roles. Enzymes lower activation energy by forming enzyme-substrate complexes.
- DNA and protein synthesis DNA is a double helix of nucleotides with complementary base pairing. Replication is semi-conservative, shown by Meselson and Stahl. Transcription makes mRNA, and translation uses tRNA and ribosomes to build polypeptides.
- Inheritance Use genetic diagrams for monohybrid crosses, including recessive conditions such as cystic fibrosis. Know the terms allele, genotype, phenotype, homozygous, heterozygous, dominant and recessive.
- Genetic screening Screening includes preimplantation genetic diagnosis, amniocentesis and chorionic villus sampling. Each has risks, and decisions raise ethical issues about consent, termination and the use of the information.
Common mistakes in Topic 2: Genes and Health
- Using Fick's law without mentioning thickness; a thinner surface increases the rate of diffusion.
- Describing the CFTR protein as a pump; it is a chloride ion channel.
- Stating that a carrier will always pass the condition to their children; two carriers have a 1 in 4 chance per pregnancy of an affected child.
- Confusing the effect of beetroot membrane permeability results; more pigment leakage means more membrane damage, shown by higher absorbance.
- Saying amniocentesis can be done earlier than chorionic villus sampling; CVS can be done earlier in pregnancy.
Try three Topic 2: Genes and Health exam-style questions
1. Two parents are both carriers of cystic fibrosis. Calculate the probability that their first two children both have cystic fibrosis. (2 marks)
Show the mark scheme answer
Probability for each child = 1/4; 1/4 x 1/4 = 1/16 (0.0625).
2. Explain how the thick mucus in cystic fibrosis reduces the efficiency of gas exchange. (3 marks)
Show the mark scheme answer
Mucus blocks bronchioles so fewer alveoli are ventilated; reduced surface area for gas exchange; concentration gradient is lower and diffusion distance may increase.
3. Describe the Meselson and Stahl experiment and explain how it supports semi-conservative replication. (4 marks)
Show the mark scheme answer
Bacteria grown in 15N then transferred to 14N; DNA extracted and centrifuged; after one generation all DNA is intermediate density; after two generations half intermediate and half light; shows each new molecule contains one original strand.
Topic 2: Genes and Health FAQs
What does Edexcel A Level Biology A Topic 2: Genes and Health cover?
It covers gas exchange, cell membranes and transport, proteins and enzymes, DNA replication, protein synthesis, mutation, monohybrid inheritance and genetic screening, using cystic fibrosis as the context.
Which paper is Topic 2 examined in?
At A Level, Year 1 topics (Topics 1 to 4) can be assessed in both Paper 1 and Paper 2, and every topic can also appear in Paper 3, which includes questions on a pre-released scientific article and practical skills.
Which core practicals are in Topic 2?
You need the investigation into the effect of temperature (or another factor) on beetroot membrane permeability using a colorimeter, and the investigation of a factor affecting the initial rate of an enzyme reaction.
