Revision Library

revisionlibrary.co.uk

GCSE · Biology

B4b Respiration, Exercise and Metabolism

AQA 8464 · Calculator allowed · about 105 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Respiration and the body's response to exercise

Revision Library

Every cell in the body needs a constant supply of energy, released from glucose by respiration. Most of the time cells respire aerobically, combining glucose with oxygen to release a large amount of energy and produce carbon dioxide and water. During vigorous exercise, the heart and lungs cannot always deliver oxygen to muscle cells fast enough to meet demand. When this happens, muscle cells respire anaerobically instead, breaking glucose down without oxygen. This releases energy more quickly than the body could otherwise supply it, but far less efficiently, and it produces lactic acid rather than carbon dioxide and water. The body responds to exercise by increasing heart rate, breathing rate and breath volume, delivering oxygen and glucose to muscles faster and removing waste products more quickly. After vigorous exercise a person keeps breathing heavily to repay an oxygen debt, the extra oxygen needed to break down the lactic acid that has built up in their muscles. Respiration is just one part of metabolism, the network of reactions that keeps an organism alive, including reactions that build carbohydrates, lipids and proteins, and break down excess amino acids into urea.

Aerobic respiration is the main way that cells release the energy they need.

(a)Define aerobic respiration.(1)

(b)Write the word equation for aerobic respiration.(2)

(c)Name the type of cell structure (organelle) in which most of the reactions of aerobic respiration take place.(1)

(Total for Question 1 is 4 marks)

During very vigorous exercise, muscle cells cannot always get enough oxygen to respire aerobically.

(a)State the word equation for anaerobic respiration in muscle cells.(2)

(b)State one situation in which muscle cells respire anaerobically rather than aerobically.(1)

(Total for Question 2 is 3 marks)

Yeast cells are single-celled fungi that can respire without oxygen. This process is called fermentation.

(a)State the word equation for anaerobic respiration (fermentation) in yeast cells.(2)

(b)Give one industrial use of fermentation by yeast.(1)

(Total for Question 3 is 3 marks)

Higher tier only. The word equation for fermentation in yeast can also be written as a balanced symbol equation.

(a)Write the balanced symbol equation for anaerobic respiration in yeast cells.(2)

(Total for Question 4 is 2 marks)

Higher tier only. The word equation for aerobic respiration can also be written as a balanced symbol equation.

(a)Balance the symbol equation for aerobic respiration by writing the correct number in front of each formula where needed: C6H12O6 + __O2 -> __CO2 + __H2O(3)

(Total for Question 5 is 3 marks)

Aerobic and anaerobic respiration both release energy from glucose, but not in the same way.

(a)State which type of respiration, aerobic or anaerobic, releases more energy from each glucose molecule.(1)

(b)Explain why aerobic respiration releases much more energy from each glucose molecule than anaerobic respiration does.(2)

(Total for Question 6 is 3 marks)

Complete the table below to compare aerobic and anaerobic respiration in human muscle cells. Each lettered blank is worth one mark.

Feature -- Aerobic respiration -- Anaerobic respiration (muscles)
Oxygen needed? -- (i) -- (ii)
Waste product(s) -- carbon dioxide and water -- (iii)
Relative energy released per glucose molecule -- (iv) -- less
Can it be sustained for a long period of exercise? -- (v) -- (vi)

(Total for Question 7 is 6 marks)

During exercise, several changes take place in the body to help meet the increased demand for energy in muscle cells.

(a)Describe how breathing rate and breath volume change during exercise.(2)

(b)Explain why breathing rate and breath volume increase during exercise.(2)

(c)Explain why heart rate increases during exercise.(2)

(Total for Question 8 is 6 marks)

A student, Priya, counted her breaths before and after exercise.
Resting: 54 breaths in 3 minutes.
Immediately after 5 minutes of moderate exercise: 108 breaths in 2 minutes.

(a)Calculate Priya's resting breathing rate, in breaths per minute.(2)

(b)Calculate Priya's breathing rate immediately after exercise, in breaths per minute.(2)

(c)Calculate the percentage increase in Priya's breathing rate caused by the exercise.(2)

(Total for Question 9 is 6 marks)

After Tomasz finishes a sprint, his body needs extra oxygen to recover.
Oxygen consumption at rest = 0.3 dm³ per minute.
During the 6 minutes immediately after the sprint, Tomasz consumed oxygen at an average rate of 1.1 dm³ per minute, before returning to his resting rate.

(a)Calculate the total volume of oxygen Tomasz consumed during the 6-minute recovery period.(2)

(b)Calculate the volume of oxygen Tomasz would have consumed at rest during the same 6 minutes.(2)

(c)Calculate the size of the oxygen debt repaid during the 6-minute recovery period.(2)

(d)Explain, in terms of lactic acid, why Tomasz's body needed this oxygen debt after the sprint.(3)

(Total for Question 10 is 9 marks)

A group of students investigated the required practical: the effect of exercise on heart rate. Aisha stepped on and off a low box repeatedly for different lengths of time, then measured her heart rate. She carried out the investigation on 03/03/2026 and repeated each reading three times.

Exercise duration (minutes) -- Repeat 1 (bpm) -- Repeat 2 (bpm) -- Repeat 3 (bpm)
0 (resting) -- 72 -- 76 -- 74
1 -- 98 -- 102 -- 100
2 -- 118 -- 152 -- 120
3 -- 134 -- 138 -- 136

(a)Identify the independent variable in this investigation.(1)

(b)Identify the dependent variable in this investigation.(1)

(c)Give three variables that should be controlled to make this a fair test.(3)

(d)Aisha counted her pulse for 15 seconds immediately after stepping, then multiplied the count by 4 to get a rate in beats per minute, rather than counting for a full 60 seconds. Explain why this method gives a more valid result.(2)

(e)One of the repeats at 2 minutes is anomalous. Identify this anomalous result and calculate the mean heart rate at 2 minutes, excluding it.(3)

(f)Describe the trend shown by Aisha's results, excluding the anomaly.(2)

(g)Aisha concluded: 'Exercise increases heart rate because muscles need more energy.' Evaluate this conclusion using your knowledge of respiration.(3)

(Total for Question 11 is 15 marks)

During a 400 m sprint, Ffion's leg muscles cannot get enough oxygen from her blood to meet demand.

(a)Name the type of respiration taking place in Ffion's leg muscles when oxygen supply cannot meet demand.(1)

(b)State the substance that builds up in Ffion's muscles as a result.(1)

(c)Explain why a build-up of this substance causes Ffion's muscles to feel fatigued.(2)

(Total for Question 12 is 4 marks)

After exercise, lactic acid must be removed from Ffion's muscles and blood.

(a)Name the organ that converts lactic acid back into glucose.(1)

(b)State what the liver needs, in addition to enzymes, in order to break down lactic acid.(1)

(c)Explain how lactic acid produced in Ffion's leg muscles reaches her liver.(2)

(Total for Question 13 is 4 marks)

Metabolism is the sum of all the reactions taking place in a cell or in the body.

(a)Define metabolism.(1)

(b)Name the storage carbohydrate that excess glucose is converted into in the liver and muscles.(1)

(c)State what happens to glucose that is not needed for respiration or converted into glycogen.(1)

(d)Explain, in terms of metabolism, why taking regular exercise can help a person control their body mass.(2)

(Total for Question 14 is 5 marks)

Metabolism includes reactions that build larger molecules from smaller ones, and reactions that break large molecules down.

(a)Name the two types of molecule that combine to form lipids (fats and oils) in metabolism.(2)

(b)Describe how plants use glucose and nitrate ions to make amino acids, and how amino acids then form proteins.(2)

(c)Excess amino acids in the human body cannot be stored, so they are broken down in the liver. Name this process, name the waste product formed, and state how this waste product is removed from the body.(2)

(Total for Question 15 is 6 marks)

The table shows the resting metabolic rate (RMR) of four people with different amounts of muscle mass.

Person -- Muscle mass (kg) -- Resting metabolic rate (kJ per day)
Kwame -- 25 -- 6800
Olivia -- 30 -- 7400
Mei -- 22 -- 6300
Dafydd -- 34 -- 7900

(a)Describe the relationship shown by the data between muscle mass and resting metabolic rate.(2)

(b)Suggest, in terms of respiration, why a person with more muscle mass has a higher resting metabolic rate.(2)

(c)A personal trainer claims: 'Building muscle through exercise will increase how much energy a client uses even when resting.' Using the data, evaluate this claim.(2)

(Total for Question 16 is 6 marks)

A 400 m runner sprints as fast as possible for the whole race. A marathon runner runs at a much slower, steady pace for over two hours.

Compare the type of respiration used by the two runners' leg muscles, and explain what happens in the sprinter's body during and after the race to deal with the effects of anaerobic respiration.

(Total for Question 17 is 6 marks)

A student investigated the rate of anaerobic respiration in yeast by measuring the volume of carbon dioxide gas produced in 5 minutes at different temperatures, using flasks of yeast and glucose solution connected to a gas syringe.

Temperature (deg C) -- Volume of CO2 collected in 5 minutes (cm³)
10 -- 4
20 -- 12
30 -- 26
40 -- 30
50 -- 6

(a)Calculate the mean rate of carbon dioxide production at 30 deg C, in cm³ per minute.(2)

(b)Describe the trend shown by the results between 10 deg C and 40 deg C.(2)

(c)Explain, in terms of enzymes, why the volume of carbon dioxide produced falls at 50 deg C compared with 40 deg C.(3)

(Total for Question 18 is 7 marks)

Mark scheme · B4b Respiration, Exercise and Metabolism

Question 1

(a) B1 the process in cells that releases energy from glucose by combining it with oxygen, oe
(a) Answer: The process in cells that releases energy from glucose by reacting glucose with oxygen (oe).
(b) B1 glucose + oxygen on the reactant side
(b) B1 carbon dioxide + water on the product side, with the arrow pointing from reactants to products
(b) Answer: glucose + oxygen -> carbon dioxide + water
(c) B1 mitochondria / mitochondrion
(c) Answer: Mitochondria (singular: mitochondrion).

Question 2

(a) B1 glucose as the only reactant (no oxygen)
(a) B1 lactic acid as the only product
(a) Answer: glucose -> lactic acid
(b) B1 during vigorous/strenuous exercise, when the oxygen supplied to the muscles cannot meet demand, oe
(b) Answer: During vigorous exercise, when the body cannot supply oxygen to the muscles fast enough to meet demand (oe).

Question 3

(a) B1 glucose as the only reactant
(a) B1 ethanol and carbon dioxide as the two products
(a) Answer: glucose -> ethanol + carbon dioxide
(b) B1 any correct use, e.g. brewing beer/wine (ethanol production) or bread-making (carbon dioxide makes the dough rise)
(b) Answer: Brewing, to produce alcoholic drinks, or bread-making, where the carbon dioxide produced makes the dough rise.

Question 4

(a) B1 C6H12O6 as the only reactant
(a) B1 2C2H5OH + 2CO2 as the products, correctly balanced
(a) Answer: C6H12O6 -> 2C2H5OH + 2CO2

Question 5

(a) B1 6O2 on the reactant side
(a) B1 6CO2 on the product side
(a) B1 6H2O on the product side
(a) Answer: C6H12O6 + 6O2 -> 6CO2 + 6H2O

Question 6

(a) B1 aerobic respiration
(a) Answer: Aerobic respiration.
(b) B1 aerobic respiration completely breaks glucose down (using oxygen) into carbon dioxide and water, oe
(b) B1 anaerobic respiration only partially breaks glucose down (into lactic acid), so most of the chemical energy remains locked inside the lactic acid molecule, oe
(b) Answer: Aerobic respiration fully breaks glucose down using oxygen, releasing all of the available chemical energy. Anaerobic respiration only partially breaks glucose down into lactic acid, so most of the energy stays locked in that molecule and is not released (oe).

Question 7

B1 (i) yes
B1 (ii) no
B1 (iii) lactic acid
B1 (iv) more
B1 (v) yes, as long as oxygen supply is sufficient, oe
B1 (vi) no, only for short bursts, because lactic acid builds up and causes fatigue, oe
Answer: (i) yes (ii) no (iii) lactic acid (iv) more (v) yes (vi) no, only for short bursts, because lactic acid builds up and causes muscle fatigue.

Question 8

(a) B1 breathing rate increases
(a) B1 breath volume (depth of breathing) increases
(a) Answer: Both breathing rate and breath volume increase during exercise.
(b) B1 to take in more oxygen (and remove carbon dioxide) more quickly, oe
(b) B1 to supply the muscles' increased demand for aerobic respiration, oe
(b) Answer: Increased breathing rate and breath volume bring more oxygen into the blood and remove carbon dioxide more quickly, to supply the muscles' increased demand for aerobic respiration (oe).
(c) B1 blood is pumped around the body faster/more often, oe
(c) B1 to deliver oxygen and glucose to the muscles faster and to remove carbon dioxide and lactic acid faster, oe
(c) Answer: A faster heart rate pumps blood around the body more quickly, delivering oxygen and glucose to the muscles faster and removing waste products, such as carbon dioxide and lactic acid, more quickly (oe).

Question 9

(a) M1 54 / 3
(a) A1 18 breaths per minute cao
(a) Answer: 18 breaths per minute
(b) M1 108 / 2
(b) A1 54 breaths per minute cao
(b) Answer: 54 breaths per minute
(c) M1 (54 - 18) / 18 x 100, ft from their (a) and (b)
(c) A1 200% cao
(c) Answer: 200%

Question 10

(a) M1 1.1 x 6
(a) A1 6.6 dm³ cao
(a) Answer: 6.6 dm³
(b) M1 0.3 x 6
(b) A1 1.8 dm³ cao
(b) Answer: 1.8 dm³
(c) M1 their (a) minus their (b), i.e. 6.6 - 1.8, ft
(c) A1 4.8 dm³ cao, ft from (a) and (b)
(c) Answer: 4.8 dm³
(d) B1 during the sprint, muscles respired anaerobically because oxygen supply could not meet demand, oe
(d) B1 this produced lactic acid, which built up in the muscles and blood, oe
(d) B1 the extra oxygen consumed during recovery is needed to break down/oxidise the lactic acid, e.g. by converting it back to glucose in the liver, oe
(d) Answer: During the sprint Tomasz's muscles respired anaerobically because oxygen could not be supplied fast enough, producing lactic acid that built up in his muscles and blood. The oxygen debt is the extra oxygen his body needs to take in afterwards to break down/oxidise this lactic acid, for example by converting it back into glucose in the liver, which is why he keeps breathing heavily and his heart rate stays high after he stops sprinting.

Question 11

(a) B1 duration of exercise (time spent stepping)
(a) Answer: The duration of exercise (the length of time spent stepping on and off the box).
(b) B1 heart rate (in beats per minute)
(b) Answer: Heart rate, measured in beats per minute (bpm).
(c) B1 the same person (Aisha) tested each time
(c) B1 the same height of box and the same stepping rate (so exercise intensity is the same) each time
(c) B1 any other valid control, e.g. full recovery back to resting heart rate before each repeat, or the same room temperature
(c) Answer: Any three of: the same person tested throughout; the same height of step and the same stepping rate, so exercise intensity is the same; a full recovery back to resting heart rate before each repeat; the same room temperature.
(d) B1 heart rate starts to fall back towards its resting value as soon as exercise stops (recovery begins immediately), oe
(d) B1 so a full 60 second count would include this falling heart rate and underestimate the rate reached during/immediately after exercise; a quick 15 second count x 4 is closer to the true rate at that moment, oe
(d) Answer: Heart rate starts to fall as soon as exercise stops, so a full 60 second count taken after stopping would include this recovery and underestimate the heart rate reached during exercise. Counting for just 15 seconds, then multiplying by 4 to convert to bpm, captures a rate much closer to the true value immediately after exercise, making it more valid (oe).
(e) M1 identifies 152 bpm as the anomalous result (much higher than the other two repeats at 2 minutes)
(e) M1 correct method excluding the anomaly, e.g. (118 + 120) / 2
(e) A1 119 bpm cao
(e) Answer: The anomalous result is 152 bpm. Mean, excluding it, = (118 + 120) / 2 = 119 bpm.
(f) B1 as exercise duration increases, heart rate increases, oe
(f) B1 reference to specific data, e.g. from about 74 bpm at rest to about 136 bpm at 3 minutes
(f) Answer: As the duration of exercise increases, Aisha's heart rate increases, rising from around 74 bpm at rest to around 136 bpm after 3 minutes of stepping (oe).
(g) B1 the data supports the general conclusion, since heart rate clearly increases as exercise duration increases, oe
(g) B1 the conclusion could be improved by explaining that muscles need more energy for aerobic respiration, which requires oxygen and glucose to be delivered faster, so the heart beats faster to supply this, oe
(g) B1 a limitation, e.g. only one person was tested, so the result may not apply to everyone, or heart rate was measured manually by counting a pulse, which is less accurate than an electronic heart rate monitor, oe
(g) Answer: The data does support Aisha's conclusion, as heart rate rises consistently as exercise duration increases. However, the conclusion could be more precise: exercising muscles need more energy for aerobic respiration, which requires oxygen and glucose to be delivered faster, so heart rate increases to pump blood around the body more quickly. The conclusion is also limited because it is based on only one person, and heart rate was measured manually by counting a pulse, which is less accurate and reliable than using an electronic heart rate monitor.

Question 12

(a) B1 anaerobic respiration
(a) Answer: Anaerobic respiration.
(b) B1 lactic acid
(b) Answer: Lactic acid.
(c) B1 lactic acid is acidic and lowers the pH inside muscle cells as it builds up, oe
(c) B1 this interferes with muscle contraction/enzyme function, causing pain, cramp and fatigue, oe
(c) Answer: Lactic acid is acidic and lowers the pH inside the muscle cells as it builds up. This interferes with muscle contraction and enzyme function, causing the muscles to feel painful, cramped and fatigued (oe).

Question 13

(a) B1 liver
(a) Answer: The liver.
(b) B1 oxygen
(b) Answer: Oxygen.
(c) B1 lactic acid diffuses out of the muscle cells into the blood plasma, down a concentration gradient, oe
(c) B1 the blood transports/carries the lactic acid to the liver, oe
(c) Answer: Lactic acid diffuses out of the muscle cells into the blood plasma, down a concentration gradient, and is then carried by the blood to the liver (oe).

Question 14

(a) B1 the sum of all the chemical reactions in a cell or the body, oe
(a) Answer: The sum of all the chemical reactions that take place in a cell, or in the body (oe).
(b) B1 glycogen
(b) Answer: Glycogen.
(c) B1 it is converted into fat/lipid for storage, oe
(c) Answer: It is converted into fat (lipid) and stored in the body.
(d) B1 exercise increases the rate of aerobic respiration in muscle cells, so more glucose is broken down for energy rather than stored, oe
(d) B1 exercise increases overall metabolic rate/energy use; if energy used is greater than energy taken in from food, stored glycogen and fat are broken down, reducing body mass, oe
(d) Answer: Exercise increases the rate of respiration in muscle cells, so more glucose is used for energy rather than being stored as glycogen or fat. It also raises the body's overall metabolic rate, so more energy is used; if this energy use is greater than the energy taken in from food, stored glycogen and fat reserves are broken down, helping to control body mass (oe).

Question 15

(a) B1 glycerol
(a) B1 fatty acids
(a) Answer: Glycerol and fatty acids.
(b) B1 glucose is combined with nitrate ions, absorbed from the soil, to form amino acids, oe
(b) B1 amino acids are joined together in long chains to form proteins, oe
(b) Answer: Plants combine glucose with nitrate ions, absorbed from the soil through their roots, to form amino acids. These amino acids are then joined together in long chains to form proteins (oe).
(c) B1 deamination, producing urea
(c) B1 urea is removed by the kidneys, in urine, oe
(c) Answer: The process is deamination, which produces urea. Urea is removed from the body by the kidneys, as a component of urine (oe).

Question 16

(a) B1 as muscle mass increases, resting metabolic rate increases (positive correlation), oe
(a) B1 reference to data, e.g. Mei has the lowest muscle mass (22 kg) and lowest RMR (6300 kJ/day), while Dafydd has the highest muscle mass (34 kg) and highest RMR (7900 kJ/day)
(a) Answer: There is a positive correlation: as muscle mass increases, resting metabolic rate increases. Mei has the lowest muscle mass (22 kg) and the lowest RMR (6300 kJ/day), while Dafydd has the highest muscle mass (34 kg) and the highest RMR (7900 kJ/day).
(b) B1 muscle tissue is more metabolically active than fat tissue / contains more mitochondria, oe
(b) B1 so more cells are respiring aerobically, releasing more energy even at rest, increasing metabolic rate, oe
(b) Answer: Muscle tissue is more metabolically active than fat tissue and contains more mitochondria, so even at rest more cells are respiring aerobically and releasing energy, giving a person with more muscle mass a higher resting metabolic rate (oe).
(c) B1 the data supports the claim, as there is a clear positive trend between muscle mass and RMR across all four people, oe
(c) B1 limitation, e.g. only four people were compared, or other factors such as age, sex or genetics that could also affect RMR were not controlled, so the data alone cannot prove the trend is caused only by muscle mass, oe
(c) Answer: The data does support the trainer's claim, since resting metabolic rate rises consistently as muscle mass increases across all four people. However, only four people were compared, and other factors that can affect RMR, such as age, sex or genetics, were not controlled, so this small dataset alone cannot prove that muscle mass is the only cause of the differences seen (oe).

Question 17

Level 1 (1-2): Basic, isolated statement(s) about one type of respiration or one runner, with little or no explanation. The answer may be a simple list.
Level 2 (3-4): Some accurate comparison between the two runners' respiration and/or some explanation of the sprinter's recovery, but the answer is incomplete or the links between ideas are not always clear.
Level 3 (5-6): A clear, logically structured comparison of aerobic and anaerobic respiration in the two runners, with a detailed and correctly linked explanation of oxygen debt and how the sprinter's body recovers.
Indicative content:
- The marathon runner's steady pace means oxygen supply can meet demand, so their leg muscles respire aerobically for the whole race
- Aerobic respiration completely breaks glucose down using oxygen, releasing a large amount of energy, and can be sustained for a long time
- The sprinter's all-out effort means oxygen demand in the leg muscles is greater than the oxygen that can be supplied
- So the sprinter's leg muscles respire anaerobically, breaking glucose down without oxygen
- Anaerobic respiration releases much less energy per glucose molecule and produces lactic acid instead of carbon dioxide and water
- Anaerobic respiration can only be sustained for a short time before lactic acid builds up and causes muscle fatigue/cramp
- After the race, the sprinter's breathing rate and heart rate remain high to repay an oxygen debt
- The oxygen debt is the extra oxygen needed to break down/oxidise the lactic acid that built up in the muscles, e.g. by converting it back to glucose in the liver
- The marathon runner will have little or no oxygen debt to repay because their muscles mostly respired aerobically throughout the race

Question 18

(a) M1 26 / 5
(a) A1 5.2 cm³ per minute cao
(a) Answer: 5.2 cm³ per minute
(b) B1 as temperature increases from 10 to 40 deg C, the volume of CO2 produced (rate of respiration) increases, oe
(b) B1 reference to data, e.g. from 4 cm³ at 10 deg C to 30 cm³ at 40 deg C
(b) Answer: As temperature increases from 10 deg C to 40 deg C, the volume of carbon dioxide produced, and so the rate of anaerobic respiration, increases, from 4 cm³ at 10 deg C up to 30 cm³ at 40 deg C.
(c) B1 the enzymes involved in respiration have gained more kinetic energy and are vibrating more, oe
(c) B1 this breaks the bonds holding the enzyme's (tertiary structure/active site) shape, so the enzyme denatures, oe
(c) B1 the substrate (glucose) can no longer fit/bind to the active site, so the rate of reaction decreases, oe
(c) Answer: At 50 deg C the respiratory enzymes in the yeast cells have gained enough kinetic energy to vibrate more, breaking the bonds that hold their active site in shape. The enzymes denature and their active sites change shape, so glucose can no longer bind to them, and the rate of respiration (and CO2 production) falls (oe).

Respiration, Exercise and Metabolism - Worksheets, Questions and Revision