Eduqas A-Level Biology Component 3 Requirements for Life: a deep dive on gas exchange, transport, nutrition, the kidney and the nervous system
A deep-dive Eduqas A-Level Biology guide to Component 3, Requirements for Life (Section A core). Covers adaptations for gas exchange, transport, and nutrition, homeostasis and the kidney, and the nervous system, with the exam patterns Eduqas repeats and a note on the Section B options.
Reviewed by: AI editorial process; not yet individually human-reviewed
Jump to a section
What Component 3 actually demands
Requirements for Life is the physiology paper of Eduqas A-Level Biology, with a compulsory Section A core and one optional Section B topic. The Section A core runs through how organisms exchange gases, transport substances, obtain nutrients, regulate their internal environment and coordinate responses. Examiners test two linked skills: precise recall of structures and sequences, and the application of those facts to data, graphs and unfamiliar contexts.
This guide walks through all five Section A 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. The Section B options are covered on the separate Options in Biology pages.
Adaptations for gas exchange
An efficient exchange surface has a large surface area, a thin barrier, a moist surface and a maintained concentration gradient. As organisms get larger, their surface-area-to-volume ratio falls, so they need specialised surfaces. Mammals use alveoli, fish use gills with counter-current flow (which keeps the oxygen gradient along the whole lamella), insects use a tracheal system, and plants use stomata. Ventilation maintains the gradient by moving the external medium.
Adaptations for transport
The mammalian heart is a double pump; the cardiac cycle (atrial systole, ventricular systole, diastole) relies on valves opening and closing by pressure differences for one-way flow. Arteries, capillaries and veins are each adapted to their role, and tissue fluid forms and is reabsorbed along a capillary. Haemoglobin loads oxygen in the lungs and unloads it at tissues, shown by the S-shaped oxygen dissociation curve; the Bohr effect shifts it right when carbon dioxide is high. In plants, xylem carries water up by cohesion-tension and phloem translocates sugars from source to sink.
Adaptations for nutrition
Autotrophs make their own food; heterotrophs consume others. In the human gut, carbohydrates, proteins and lipids are digested by hydrolysis using specific enzymes (amylase and disaccharidases; endo-, exo- and dipeptidases; lipase after bile emulsifies fats). The small intestine is adapted for absorption with villi and microvilli (surface area), a thin epithelium, a good blood supply and mitochondria for active transport (such as glucose co-transport with sodium).
Homeostasis and the kidney
Homeostasis maintains a constant internal environment by negative feedback. The kidney filters the blood in nephrons: ultrafiltration in the renal capsule (high pressure from a wide afferent and narrow efferent arteriole), selective reabsorption in the proximal tubule, and water conservation by the loop of Henle (a counter-current multiplier making the medulla salty). Osmoregulation by ADH adjusts the collecting duct's permeability, so low blood water potential gives concentrated urine.
The nervous system
A neurone carries an impulse: the resting potential (about minus 70 millivolts, maintained by the sodium-potassium pump) is reversed in an all-or-nothing action potential (sodium in, then potassium out). The impulse is propagated as local currents, faster in myelinated neurones by saltatory conduction. At a synapse, calcium entry releases neurotransmitter (such as acetylcholine), which depolarises the next neurone; the reflex arc gives a fast automatic response.
How Component 3 is examined
A typical Eduqas profile for Requirements for Life:
- Recall and sequence. The cardiac cycle, ultrafiltration and reabsorption, and the action potential and synapse.
- Graphs. The cardiac-cycle pressure graph and the oxygen dissociation curve (including the Bohr shift).
- Applied and data questions. Counter-current versus parallel flow, glucose in the urine, or the effect of a synapse-blocking drug.
- Levels-of-response QER. The cardiac cycle, ultrafiltration and osmoregulation, or the action potential and synaptic transmission make predictable extended-response questions.
Check your knowledge
A mix of recall and application questions covering the Section A core of Component 3. Attempt them under timed conditions, then check against the solutions.
- State three features of an efficient gas exchange surface. (3 marks)
- Explain why the atrioventricular valves close during ventricular systole. (2 marks)
- State what the Bohr effect does to the oxygen dissociation curve and why it is useful. (2 marks)
- Name the enzymes that digest a protein to amino acids in the gut. (3 marks)
- Explain why plasma proteins are not found in the glomerular filtrate. (2 marks)
- Explain the role of ADH when the blood water potential falls too low. (3 marks)
- State the value of the resting potential and what maintains it. (2 marks)
- State the role of calcium ions in synaptic transmission. (1 mark)