A-Level A-Level Biology 2 — Questions and Answers
Question 1: What is the Hardy-Weinberg principle?
- A model describing the process of natural selection
- A model stating that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary influences (Correct answer)
- A law of inheritance for monohybrid crosses
- A description of genetic drift
Correct answer: A model stating that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary influences
The Hardy-Weinberg principle states that allele and genotype frequencies remain constant in large, randomly mating populations with no mutation, migration, selection, or genetic drift. Equations: p + q = 1 and p² + 2pq + q² = 1.
Question 2: What is the role of restriction enzymes in genetic engineering?
- To join DNA fragments together
- To cut DNA at specific recognition sequences, producing fragments for cloning (Correct answer)
- To replicate DNA in a PCR machine
- To transcribe DNA into mRNA
Correct answer: To cut DNA at specific recognition sequences, producing fragments for cloning
Restriction endonucleases cut double-stranded DNA at specific palindromic recognition sequences (4–8 base pairs), often producing 'sticky ends' that allow fragments to be joined to vectors using DNA ligase.
Question 3: What is ecological succession?
- The daily changes in an ecosystem
- The process by which communities of organisms change and develop over time in a habitat, from pioneer species to a climax community (Correct answer)
- A type of nutrient cycling
- Random migration of species
Correct answer: The process by which communities of organisms change and develop over time in a habitat, from pioneer species to a climax community
Ecological succession is the directional change in a community over time. Primary succession starts on bare substrate (e.g., rock after a glacier). Species modify the habitat, allowing new species to establish, eventually reaching a stable climax community.
Question 4: What is the difference between Type I and Type II diabetes?
- They are the same condition
- Type I is an autoimmune condition destroying beta cells; Type II is insulin resistance often linked to lifestyle (Correct answer)
- Type II is more severe and has no treatment
- Type I only affects adults over 40
Correct answer: Type I is an autoimmune condition destroying beta cells; Type II is insulin resistance often linked to lifestyle
Type I (insulin-dependent) diabetes is autoimmune — the immune system destroys pancreatic beta cells, stopping insulin production. Type II develops when cells become resistant to insulin, often linked to obesity and lifestyle, though genetics plays a role.
Question 5: What is the function of the glomerulus in the nephron?
- Reabsorbing glucose and amino acids
- Ultrafiltration of blood under pressure to produce glomerular filtrate (Correct answer)
- Secreting hormones
- Producing urine by active transport
Correct answer: Ultrafiltration of blood under pressure to produce glomerular filtrate
The glomerulus is a knot of capillaries inside the Bowman's capsule. High hydrostatic pressure forces small molecules (water, urea, glucose, ions) out of the blood into the Bowman's capsule as filtrate. Large proteins and cells cannot pass.
Question 6: What is an action potential?
- The resting potential of a neurone
- A temporary reversal of the electrical charge across a neurone's membrane, allowing a nerve impulse to travel (Correct answer)
- A chemical signal at a synapse
- The refractory period of a nerve fibre
Correct answer: A temporary reversal of the electrical charge across a neurone's membrane, allowing a nerve impulse to travel
An action potential is a rapid, all-or-nothing depolarisation of the neurone membrane. Na⁺ channels open (depolarisation → +40mV), then K⁺ channels open (repolarisation), followed by a refractory period. The threshold is approximately −55mV.
A-Level A-Level Biology 2
What is the Hardy-Weinberg principle?