topic overview

Question 1

Why is cellular respiration necessary for cells? (2)

Answer 1

Respiration releases energy from glucose, which is used to power biological processes,

Without this energy, biological processes would stop, and the organism would die

Question 2

What biological processes rely on cellular respiration? (6)

Answer 2

Active transport (e.g. mineral ions into plant root hair cells), -

Secretion (e.g. large molecules by exocytosis),

Endocytosis (bulk movement of large molecules into cells), -

Anabolism (synthesis of large molecules from smaller ones), -

Replication of DNA, - Cell division,

Movement (e.g. muscle contraction, flagella, and cilia movement)

Question 3

What is the role of the double membrane in the mitochondrion? (3)

Answer 3

The double membrane controls the entry and exit of substances,

The outer membrane separates mitochondrial contents from the rest of the cell,

The inner membrane contains electron transport chains and ATP synthase

Question 4

What are cristae, and what is their function in the mitochondrion? (3)

Answer 4

Folds of the inner mitochondrial membrane,

They provide a large surface area for oxidative phosphorylation,

Which increases the surface available for enzymes and proteins involved in ATP production

Question 5

What is the mitochondrial matrix, and what does it contain? (3)

Answer 5

The fluid inside the mitochondrion,

It contains proteins, lipids, ribosomes, enzymes for aerobic respiration, and mitochondrial DNA,

Which allows the mitochondrion to control the production of some of its own proteins

Question 6

What are the 4 stages of aerobic respiration and where do they take place? (4)

Answer 6

1. Glycolysis - in the cytoplasm,
2. Link reaction - in the matrix of the mitochondria,
3. Krebs cycle - in the matrix of the mitochondria,
4. Oxidative phosphorylation - on the cristae of the mitochondria

Question 7

What is the purpose of glycolysis? (3)

Answer 7

To convert glucose (6C) into pyruvate (3C), which can be transported into the mitochondria,

Glycolysis occurs in the cytoplasm and is the first stage of both aerobic and anaerobic respiration,

It is an anaerobic process (does not require oxygen)

Question 8

What are the two stages of glycolysis? (2)

Answer 8

1. Phosphorylation,
2. Oxidation

Question 9

Describe what happens during the phosphorylation stage of glycolysis (3)

Answer 9

1. 2 ATP molecules are used to add 2 phosphate groups to glucose (6C),
2. Forming hexose bisphosphate,
3. Hexose bisphosphate splits into 2 molecules of triose phosphate (3C)

Question 10

Describe what happens during the oxidation stage of glycolysis (3)

Answer 10

1. Triose phosphate is oxidised, forming 2 molecules of pyruvate,
2. NAD is reduced to form 2 reduced NAD,
3. 4 ATP are produced via substrate-level phosphorylation

Question 11

How much ATP is produced during glycolysis? (2)

Answer 11

4 ATP are produced, but 2 ATP are used in the first step, resulting in a net gain of 2 ATP,

The ATP is produced via substrate-level phosphorylation (direct transfer of a phosphate group to ADP)

Question 12

What are the products of glycolysis? (3)

Answer 12

2 ATP,
2 reduced NAD,
2 pyruvate

Question 13

What is the link reaction known as and where does it take place? (2)

Answer 13

Oxidative decarboxylation,

It occurs in the mitochondrial matrix

Question 14

Describe the link reaction (3)

Answer 14

1. Pyruvate is oxidised (loses hydrogen) and decarboxylated (loses CO₂) to form acetate,
2. Acetate combines with coenzyme A to form acetyl CoA,
3. CO₂ and reduced NAD are produced, but no ATP is made

Question 15

Where does the Krebs cycle take place? (1)

Answer 15

Mitochondrial matrix

Question 16

Describe the basics of the Krebs cycle (4)

Answer 16

1. It starts when acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C),
2. Citrate undergoes a series of reactions,
3. Losing CO₂ and hydrogen (dehydrogenation and decarboxylation),
4. To regenerate oxaloacetate and produce ATP, reduced NAD, and reduced FAD

Question 17

What happens to citrate in the Krebs cycle? (4)

Answer 17

1. Citrate (6C) loses CO₂ and H₂,
2. To form a 5C molecule (decarboxylation and dehydrogenation),
3. The 5C molecule is further decarboxylated and dehydrogenated, producing 1 reduced FAD, 2 reduced NAD, and 1 ATP (via substrate-level phosphorylation),
4. Oxaloacetate is regenerated to start the cycle again

Question 18

What is the role of coenzymes in cellular respiration? (4)

Answer 18

Coenzymes like NAD and FAD assist in oxidation reactions by transferring hydrogen atoms, -

These coenzymes carry hydrogen to the inner mitochondrial membrane, -

Where they split into H⁺ ions and electrons for oxidative phosphorylation,

NAD and FAD are re-oxidised and can be reused in the earlier stages of respiration

Question 19

What are the key differences between NAD and FAD in respiration? (3)

Answer 19

NAD participates in all stages of respiration, while FAD only accepts hydrogens during the Krebs cycle,

NAD accepts 1 hydrogen, while FAD accepts 2 hydrogens, -

Reduced NAD generates 2.5 ATP molecules, and reduced FAD generates 1.5 ATP molecules

Question 20

What is the role of coenzyme A (CoA) in respiration? (2)

Answer 20

Coenzyme A carries acetate groups (made from pyruvate during the link reaction) into the Krebs cycle,

It can also carry acetate groups made from fatty acids or amino acids into the Krebs cycle

Question 21

What is oxidative phosphorylation, and where does it occur? (3)

Answer 21

Oxidative phosphorylation occurs along the inner mitochondrial membrane,

It involves the transfer of electrons down an electron transport chain to generate ATP,

Reduced NAD and reduced FAD are oxidised, releasing protons (H⁺) and electrons (e⁻)

Question 22

How do electrons contribute to ATP synthesis in oxidative phosphorylation? (4)

Answer 22

1. Electrons are passed along a chain of electron transfer carriers in a series of redox reactions,
2. As electrons move down the chain, they release energy,
3. Used to actively transport protons across the inner mitochondrial membrane into the intermembrane space,
4. Creating an electrochemical gradient

Question 23

What is chemiosmosis in oxidative phosphorylation? (3)

Answer 23

1. The process of ATP production driven by the movement of protons (H⁺) across the membrane,
2. Protons diffuse back into the mitochondrial matrix through ATP synthase,
3. Driving the synthesis of ATP from ADP + Pi

Question 24

What is the role of oxygen in oxidative phosphorylation? (3)

Answer 24

1. Oxygen is the final electron acceptor in the electron transport chain,
2. At the end of the chain, electrons, protons (H⁺), and oxygen combine,
3. To form water (H₂O)

Question 25

What happens during lactate fermentation in mammals? (2)

Answer 25

Reduced NAD transfers hydrogen to pyruvate to form lactate and NAD, NAD can be reused in glycolysis, allowing the process to continue even without oxygen

Question 26

What happens during alcoholic fermentation in yeast and plants? (3)

Answer 26

1. CO₂ is removed from pyruvate to form ethanal, 2. Reduced NAD transfers hydrogen to ethanal, forming ethanol and NAD, 3. NAD can be reused in glycolysis

Question 27

What are the similarities between anaerobic respiration in yeast/plants and animals? (2)

Answer 27

Both produce ATP, Both regenerate oxidised NAD

Question 28

What are the differences between anaerobic respiration in yeast/plants and animals? (2)

Answer 28

Yeast/plants form ethanol, while animals form lactate, CO₂ is released by yeast/plants, but not in animal cells

Question 29

Why is the ATP yield lower in anaerobic respiration compared to aerobic respiration? (4)

Answer 29

Anaerobic respiration only includes glycolysis, Which produces 2 ATP per glucose molecule, The energy-releasing reactions of the Krebs cycle and oxidative phosphorylation, Require oxygen and don't occur during anaerobic respiration

Question 30

How can you measure the rate of CO₂ production via aerobic respiration in yeast? (6)

Answer 30

1. Add known volume/concentration of substrate solution (e.g. glucose) to a test tube, 2. Add buffer solution to maintain constant pH, 3. Place in a water bath at 25°C for 10 minutes, 4. Add a known mass of yeast and stir, 5. Attach a gas syringe to the test tube, 6. Record the volume of CO₂ in the syringe at regular intervals to monitor the rate of respiration

Question 31

What should be included in the control experiment and why should the experiment be repeated? (3)

Answer 31

The control experiment should have the same setup but with no yeast, Ensuring no CO₂ production without yeast, The experiment should be repeated three times to calculate a mean rate of CO₂ production for more reliable results

Question 32

How can you measure the rate of CO₂ production via anaerobic respiration in yeast? (3)

Answer 32

1. Set up the apparatus as in the aerobic experiment, 2. But add liquid paraffin to cover the solution, stopping oxygen from reaching the yeast, 3. Insert the bung attached to the gas syringe and record the CO₂ production

Question 33

How do the energy values of carbohydrates, lipids, and proteins compare as respiratory substrates? (3)

Answer 33

Lipids contain the most hydrogen atoms per unit mass, so they produce the most ATP, Proteins have fewer hydrogen atoms and produce less ATP than lipids, Carbohydrates have the least hydrogen atoms and the lowest energy value

Question 34

How is the respiratory quotient (RQ) calculated, and what does it represent? (2)

Answer 34

RQ = volume of CO₂ released / volume of O₂ consumed, It represents the ratio of carbon dioxide produced to oxygen consumed during respiration

Question 35

What are the typical RQ values for carbohydrates, proteins, and lipids? (3)

Answer 35

Carbohydrates (e.g. glucose): RQ = 1, Proteins/amino acids: RQ ≈ 0.9, - Lipids (triglycerides): RQ ≈ 0.7

Question 36

How can a respirometer be used to measure the rate of respiration in an organism like woodlice? (3)

Answer 36

1. A respirometer measures oxygen consumption by tracking the movement of coloured liquid in the manometer, 2. CO₂ is absorbed by potassium hydroxide, and the decrease in air volume causes the liquid to move toward the test tube with the organism, 3. The volume of oxygen consumed per minute can be calculated based on the distance moved by the liquid and the diameter of the capillary tube

Question 37

What variables need to be controlled in a respirometer experiment to ensure accurate results? (4)

Answer 37

Temperature, Volume of potassium hydroxide solution in each tube, - Age/sex/mass of the organisms used, The experiment should be repeated, and a mean volume of oxygen consumption should be calculated

Question 38

What are the advantages of using electronic oxygen sensors and data loggers in respirometer experiments? (5)

Answer 38

Greater precision in measurements, Results are not subjective, - Smaller percentage error, Data can be stored for later analysis, More frequent time intervals can be recorded, improving the accuracy of results

Question 39

Summarise where the products of glycolysis are transported / used for (6)

Answer 39

2 NADH: oxidative phosphorylation 2 pyruvate: actively transported into the matrix for link reaction 2 ATP: used for energy

Question 40

Summarise where the products of link reaction are transported / used for (6)

Answer 40

2 acetyl CoA: krebs cycle 2 CO2: released as waste 2x NADH: oxidative phosphorylation

Question 41

Summarise where the products of the krebs cycle are transported / used for (6)

Answer 41

2 CoA enzyme: back to link reaction to be reused 2x 4C compound: ready to combine with acetyl CoA for use in next krebs cycle 4x CO2: released as waste 2 ATP: used as energy 6 NADH: oxidative phosphorylation 2 FADH: oxidative phosphorylation

Question 42

How many molecules of ATP are produced from reduced NAD during oxidative phosphorylation? (3)

Answer 42

Each reduced NAD can make 2.5 ATP molecules 10 reduced NAD from glycolysis, the link reaction, and the Krebs cycle Can produce 25 ATP in total

Question 43

How many molecules of ATP are produced from reduced FAD during oxidative phosphorylation? (2)

Answer 43

Each reduced FAD can make 1.5 ATP molecules 2 reduced FAD from the Krebs cycle can produce 3 ATP in total

Question 44

How many total ATP molecules are produced in aerobic respiration? (4)

Answer 44

32 ATP in total 4 ATP from substrate-level phosphorylation 28 ATP from oxidative phosphorylation 25 ATP from reduced NAD and 3 ATP from reduced FAD