AQA GCSE Biology 8461: Bioenergetics – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 4.4 Bioenergetics (4.4.1.1 to 4.4.2.3) of the AQA GCSE Biology (8461) specification, for teaching from September 2016 and exams from 2018 onwards. The topic is assessed on Paper 1, set at Foundation and Higher Tier. Questions 5, 6 and 7, and parts 3(d), 10(b) and 10(c), test content the specification marks (HT only) and are labelled Higher tier only. Question 3 is based on required practical 6.

Learn the content first in the Bioenergetics study guide and the revision notes. The course hub is AQA GCSE Biology, and the printable checklist lists every point.

Questions

1.

(a) Write the word equation for photosynthesis. [2] (b) Give the chemical formula of glucose. [1] (c) Explain why photosynthesis is described as an endothermic reaction. [1]

2. Describe three ways a plant uses the glucose it makes, and explain why the plant also needs nitrate ions from the soil. [4]

3. A student investigates the effect of light intensity on the rate of photosynthesis in pondweed. She counts oxygen bubbles for one minute, three times at each distance.

Distance of lamp (cm)	10	20	30	40
Bubbles per minute, reading 1	52	29	16	9
Bubbles per minute, reading 2	50	31	15	8
Bubbles per minute, reading 3	51	22	17	10

(a) Identify the anomalous result, and calculate the mean rate at 20 cm without it. [2] (b) In a later run at 40 cm, she counts 27 bubbles in 3 minutes. Calculate the rate. Give the unit. [2] (c) She places a beaker of water between the lamp and the pondweed. Explain why. [2] (d) (Higher tier only) Calculate 1/d² for a distance of 20 cm. [1] (e) Explain why the rate falls as the lamp is moved further away. [2]

4. Describe and explain how temperature affects the rate of photosynthesis. [3]

5. (Higher tier only) A light meter reads 800 lux at 15 cm from a lamp.

(a) Use the inverse square law to calculate the reading at 30 cm. [2] (b) When the lamp was moved from 15 cm to 30 cm, the rate of photosynthesis fell by much less than three quarters. Suggest why. [2]

6. (Higher tier only) A scientist measures the rate of photosynthesis at two carbon dioxide concentrations. Temperature is kept constant.

Light intensity (arbitrary units)	1	2	3	4	5
Rate at 0.04% CO₂ (arbitrary units)	10	20	26	27	27
Rate at 0.10% CO₂ (arbitrary units)	10	20	30	40	40

(a) Identify the limiting factor at light intensity 1. Explain your answer. [2] (b) Identify the limiting factor at light intensity 5 at 0.04% CO₂. Explain your answer. [2] (c) Suggest what limits the rate at light intensity 5 at 0.10% CO₂. [1]

7. (Higher tier only) A lettuce grower sells lettuce at £2.50 per kg. A paraffin heater costs £84 a week to run and increases yield by 40 kg a week. Extra lamps would cost £60 a week and increase yield by a further 12 kg a week.

(a) Calculate the weekly gain or loss from using the heater. [2] (b) Calculate the weekly gain or loss from adding the lamps. [2] (c) Explain why the lamps increase yield so little. [2]

8. Yeast is used to make bread.

(a) Write the word equation for anaerobic respiration in yeast. [2] (b) In an investigation, yeast released 18 cm³ of carbon dioxide in 6 minutes at 25 °C and 42 cm³ in 6 minutes at 35 °C. Calculate the rate at each temperature. [2] (c) Explain why anaerobic respiration in yeast makes bread dough rise. [2]

9. A student measures her breathing at rest and during exercise.

	At rest	During exercise
Breathing rate (breaths per minute)	15	36
Breath volume (dm³)	0.5	2.0

(a) Calculate the percentage increase in breathing rate. [2] (b) Calculate the volume of air breathed per minute at rest and during exercise. [2] (c) Explain why breathing rate, breath volume and heart rate increase during exercise. [3]

10. A runner completes a long race.

(a) Compare aerobic respiration with anaerobic respiration in muscles. [4] (b) (Higher tier only) At rest the runner uses 0.3 dm³ of oxygen per minute. For 10 minutes after the race, she uses a mean of 1.1 dm³ per minute. Calculate her oxygen debt. [2] (c) (Higher tier only) Explain what happens to the lactic acid after the race, and why extra oxygen is needed. [3]

11.

(a) Define metabolism. [1] (b) Describe how a plant makes lipids and proteins. [3] (c) Name the substance formed when excess proteins are broken down. [1] (d) Explain why metabolism depends on respiration. [1]

Answers

1. (a) carbon dioxide + water [1]; → glucose + oxygen, with light above the arrow [1] (b) C₆H₁₂O₆ [1] (c) Energy is transferred from the environment to the chloroplasts by light [1] Examiner insight: Writing light as a reactant (“+ light”) in (a) usually loses the reactant mark; it belongs above the arrow.

2. Any three from: respiration; converted to insoluble starch for storage; made into fat or oil for storage; made into cellulose to strengthen cell walls; made into amino acids for protein synthesis [1] [1] [1]; nitrate ions are needed with glucose to make amino acids, and so proteins [1] Examiner insight: “Stored as glucose” earns nothing; the storage form must be starch, or fat or oil.

3. (a) 22 is anomalous [1]; mean = (29 + 31) ÷ 2 = 30 bubbles per minute [1] (b) 27 ÷ 3 = 9 [1]; 9 bubbles per minute [1] (c) It absorbs heat from the lamp, keeping the temperature constant [1]; so only light intensity affects the rate, making it a fair test [1] (d) 1/20² = 1/400 = 0.0025 [1] (e) Light intensity decreases [1]; so less energy is transferred for photosynthesis and light is the limiting factor [1] Examiner insight: In (b) the unit is part of the answer; a bare “9” gets the method mark only.

4. As temperature rises, the rate increases, because enzyme-controlled reactions go faster [1]; the rate is highest at the optimum temperature [1]; above the optimum, enzymes are denatured, so the rate falls sharply [1] Examiner insight: “Enzymes are killed” is not accepted; the word needed is denatured.

5. (a) 800 × (15 ÷ 30)² [1] = 200 lux [1] (b) At 15 cm light was not the limiting factor [1]; another factor, such as CO₂ concentration or temperature, was limiting, so the rate did not fall in proportion to light intensity [1] Examiner insight: Halving the reading to 400 lux scores zero in (a); the inverse square law needs the squared ratio.

6. (a) Light intensity [1]; the rate is the same at both CO₂ concentrations, and rises as light increases [1] (b) Carbon dioxide concentration [1]; the rate no longer rises with light, but it is higher at 0.10% CO₂ at the same light intensity [1] (c) Temperature, or amount of chlorophyll [1] Examiner insight: A named factor needs data-based evidence for the second mark; quote where the lines are equal or where one levels off.

7. (a) Income = 40 × 2.50 = £100 [1]; gain = 100 − 84 = £16 a week [1] (b) Income = 12 × 2.50 = £30 [1]; 30 − 60 = a loss of £30 a week [1] (c) Light is no longer the main limiting factor [1]; another factor, such as CO₂ concentration, limits the rate, so extra light gives little extra photosynthesis [1] Examiner insight: In (b), a correct method with the sign wrong (a “gain of £30”) usually keeps the method mark and loses the answer mark.

8. (a) glucose → [1]; ethanol + carbon dioxide [1] (b) 18 ÷ 6 = 3 cm³ per minute at 25 °C [1]; 42 ÷ 6 = 7 cm³ per minute at 35 °C [1] (c) Carbon dioxide is produced [1]; the gas is trapped as bubbles in the dough, so it rises [1] Examiner insight: Giving lactic acid as a product of yeast is a contradiction that loses the equation mark.

9. (a) (36 − 15) ÷ 15 × 100 [1] = 140% [1] (b) Rest: 15 × 0.5 = 7.5 dm³ per minute [1]; exercise: 36 × 2.0 = 72 dm³ per minute [1] (c) Muscles need more energy for contraction [1]; so more aerobic respiration is needed [1]; the changes supply the muscles with more oxygenated blood [1] Examiner insight: Dividing by 36 in (a) is the usual slip; the original value always goes on the bottom.

10. (a) Aerobic needs oxygen; anaerobic does not [1]; aerobic produces carbon dioxide and water; anaerobic in muscles produces lactic acid [1]; aerobic oxidises glucose completely; anaerobic incompletely [1]; aerobic transfers much more energy [1] (b) Extra oxygen per minute = 1.1 − 0.3 = 0.8 dm³ [1]; 0.8 × 10 = 8 dm³ [1] (c) Blood carries lactic acid to the liver [1]; where it is converted back into glucose [1]; extra oxygen is needed to react with the accumulated lactic acid and remove it from the cells [1] Examiner insight: A “compare” answer needs both sides of each point; listing aerobic facts alone scores at most half in (a).

11. (a) The sum of all the reactions in a cell or the body [1] (b) One glycerol molecule joins with three fatty acid molecules to form a lipid [1]; glucose and nitrate ions form amino acids [1]; amino acids are joined to make proteins [1] (c) Urea [1] (d) Respiration transfers the energy used to synthesise new molecules [1] Examiner insight: “Fats are made from fatty acids” alone misses the glycerol and the one-to-three ratio, so it does not earn the lipid mark.

Where marks are usually lost

• Putting light into the photosynthesis equation as a reactant.
• Calling photosynthesis exothermic or respiration endothermic.
• Writing that anaerobic respiration in muscles produces carbon dioxide.
• Saying anaerobic respiration releases no energy, instead of much less.
• Missing units on rates, or dividing time by amount.
• Naming a limiting factor without quoting evidence from the table or graph.
• (Higher tier only) Halving instead of quartering light intensity when the distance doubles.
• (Higher tier only) Reporting a greenhouse loss as a gain, or comparing yield instead of money.
• Forgetting the heat shield, or not linking it to keeping temperature constant, in required practical 6.

Next steps

• Bioenergetics revision notes
• Bioenergetics study guide
• AQA GCSE Biology course hub
• Printable AQA GCSE Biology checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA GCSE Biology (8461) specification, Version 1.0, for teaching from September 2016 and exams from 2018 onwards (AQA), section 4.4 Bioenergetics.