A-Level Biology Flashcards

What is the Hardy-Weinberg principle?

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.

What is the role of restriction enzymes in genetic engineering?

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.

What is ecological succession?

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.

What is the difference between Type I and Type II diabetes?

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.

What is the function of the glomerulus in the nephron?

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.

What is an action potential?

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.