WJEC A Level Biology
WJEC A Level Biology Unit 3: Energy, Homeostasis and the Environment Exam Questions
Free WJEC A Level Biology exam questions for Unit 3: Energy, Homeostasis and the Environment, with a mark scheme for every pack. Covers ATP and chemiosmosis, photosynthesis, respiration, microbiology, ecosystems, human impact, the kidney and osmoregulation, and the nervous system.
Unit 3: Energy, Homeostasis and the Environment 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.
StemUp mark scheme flashcards
A-Level Biology Flashcards for 2027 Onwards
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
From £10.99View flashcards
About WJEC A Level Biology Unit 3: Energy, Homeostasis and the Environment
Unit 3 of WJEC A Level Biology, Energy, Homeostasis and the Environment, is the first A2 unit. It brings together energy release and capture with control systems and ecology. It covers ATP and chemiosmosis, photosynthesis and respiration, culturing microorganisms, populations and ecosystems, human impact on the environment, the kidney and osmoregulation, and the nervous system. It builds on enzymes, membranes and organelles from Unit 1. Examiners often set data questions on limiting factors, RQ and respirometers, serial dilution calculations, nitrogen cycle reasoning, nephron function, and the generation and transmission of nerve impulses.
What you need to know
- 3.1 ATP structure and hydrolysis, and the chemiosmotic theory: proton gradients across membranes drive ATP synthase.
- 3.2 Absorption and action spectra, photosystems, cyclic and non-cyclic photophosphorylation, the Calvin cycle with rubisco, RuBP, GP and TP, and limiting factors.
- 3.3 Glycolysis, link reaction, Krebs cycle and electron transport chain, anaerobic respiration, alternative respiratory substrates and respiratory quotient.
- 3.4 Classifying bacteria, culturing with aseptic technique, and estimating numbers with serial dilution, plate counts and haemocytometers.
- 3.5 and 3.6 Population growth and limiting factors, energy flow and productivity, carbon and nitrogen cycles, succession, and human impacts such as deforestation, overfishing and agricultural change, with conservation strategies.
- 3.7 Nephron structure, ultrafiltration, selective reabsorption, the loop of Henle, ADH and osmoregulation, and adaptations of animals to different environments.
- 3.8 Nerve nets, reflex arcs, neurone structure, resting and action potentials, saltatory conduction, synapses and the effects of drugs.
Common mistakes in Unit 3: Energy, Homeostasis and the Environment
- Saying cyclic photophosphorylation produces reduced NADP. Cyclic photophosphorylation involves only photosystem I and produces ATP only.
- Placing glycolysis in the mitochondria. Glycolysis happens in the cytoplasm; pyruvate then enters the mitochondrial matrix.
- Writing that denitrifying bacteria add nitrates to soil. Denitrifying bacteria convert nitrates to nitrogen gas, usually in anaerobic conditions.
- Describing ADH as being released from the hypothalamus. ADH is produced in the hypothalamus but released from the posterior pituitary.
- Saying a synapse allows impulses to pass in both directions. Transmission is one-way because neurotransmitter is released only from the presynaptic membrane and receptors are only on the postsynaptic membrane.
Try three Unit 3: Energy, Homeostasis and the Environment exam-style questions
1. In a respirometer, organisms produced 4.2 cm3 of carbon dioxide and used 6.0 cm3 of oxygen. Calculate the RQ and suggest the substrate. (2 marks)
Show the mark scheme answer
RQ = 4.2 / 6.0 = 0.70; lipid.
2. Explain how the loop of Henle allows mammals to produce concentrated urine. (4 marks)
Show the mark scheme answer
Ascending limb actively transports sodium and chloride ions out into the medulla; ascending limb is impermeable to water; this lowers the water potential of the medulla; water leaves the descending limb and collecting duct by osmosis; a longer loop gives a steeper gradient.
3. Describe the role of microorganisms in the nitrogen cycle. (4 marks)
Show the mark scheme answer
Nitrogen-fixing bacteria such as Rhizobium convert nitrogen gas to ammonium; saprobionts convert proteins in dead matter to ammonium (ammonification); nitrifying bacteria oxidise ammonium to nitrite and then nitrate; denitrifying bacteria convert nitrate to nitrogen gas.
Unit 3: Energy, Homeostasis and the Environment FAQs
What does WJEC A Level Biology Unit 3: Energy, Homeostasis and the Environment cover?
ATP, photosynthesis, respiration, microbiology, population size and ecosystems, human impact on the environment, homeostasis and the kidney, and the nervous system.
Is Unit 3 an AS or A2 unit?
Unit 3 is an A2 unit assessed by a written exam, and it can draw synoptically on AS content.
Which calculations should I practise for Unit 3?
Respiratory quotient, efficiency of energy transfer, serial dilution counts, rates of photosynthesis from gas volumes and percentage changes in population data.
