Level 2 — RecallCellular Respiration

Cellular Respiration

40 marksprintable — key stays hidden on paper

Level 2 Test Paper (Recall & Short Answer)

Time allowed: 30 minutes Total marks: 40

Answer all questions. Show working where calculations are required. Use $...$ notation for equations.

Question 1. Write the balanced overall equation for aerobic respiration of glucose, including the energy term. (4 marks)

Question 2. Glycolysis takes place in the cytoplasm. (a) State the inputs (reactants) required for glycolysis. (2 marks) (b) State the net outputs (products) of glycolysis per glucose molecule. (3 marks)

Question 3. Explain what happens during pyruvate oxidation (the link reaction). In your answer, state where it occurs and name the products. (4 marks)

Question 4. For one turn of the Krebs cycle: (a) State the molecules that enter the cycle. (2 marks) (b) List all the products released per turn. (4 marks)

Question 5. The electron transport chain (ETC) is located in the inner mitochondrial membrane. (a) State the two molecules that donate electrons to the ETC. (2 marks) (b) State the final electron acceptor and the molecule formed when it accepts electrons and protons. (2 marks)

Question 6. Describe chemiosmosis and the role of ATP synthase in ATP production. (4 marks)

Question 7. Calculate the theoretical maximum ATP yield from the complete aerobic respiration of one glucose molecule. Show the contribution from each stage. (5 marks)

Question 8. Complete the table distinguishing aerobic and anaerobic respiration. (4 marks)

Feature	Aerobic	Anaerobic
Requires oxygen?
ATP yield per glucose
Final products (in animals)
Location

Question 9. (a) Write the word equation for lactic acid fermentation in muscle cells. (2 marks) (b) Write the word equation for alcoholic fermentation in yeast. (2 marks)

Question 10. Explain the role of $NAD^+$ and $FAD$ as electron carriers in respiration. (3 marks)

End of paper

Answer keyMark scheme & solutions

Question 1. (4 marks) $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

Correct reactants glucose + oxygen (1)
Correct products CO₂ + water (1)
Correct coefficients (6O₂, 6CO₂, 6H₂O) (1)
Energy/ATP term included (1)

Question 2. (5 marks) (a) Inputs: glucose (1); 2 ATP (to prime/phosphorylate), 2 $NAD^+$ , 2 ADP + Pi, inorganic phosphate — award for glucose + ATP + NAD⁺ (2) (b) Net outputs per glucose: 2 pyruvate (1); 2 ATP net (4 made − 2 used) (1); 2 NADH (+ 2H⁺) (1)

Question 3. (4 marks)

Occurs in the mitochondrial matrix (1)
Pyruvate (3C) is decarboxylated — one CO₂ released (1)
It is oxidised, reducing $NAD^+$ to NADH (1)
Remaining 2C acetyl group joins coenzyme A to form acetyl-CoA (1)

Question 4. (6 marks) (a) Inputs: acetyl-CoA (2C) (1); oxaloacetate (4C) to combine forming citrate (1) (b) Products per turn: 2 CO₂ (1); 3 NADH (1); 1 FADH₂ (1); 1 ATP (or GTP) (1)

Question 5. (4 marks) (a) NADH and FADH₂ (1 each = 2) (b) Final acceptor: oxygen / $O_2$ (1); forms water / $H_2O$ (1)

Question 6. (4 marks)

Electrons pass along carriers, releasing energy used to pump $H^+$ (protons) from matrix into intermembrane space (1)
This creates a proton (electrochemical/H⁺) gradient across the inner membrane (1)
Protons flow back down the gradient through ATP synthase (chemiosmosis) (1)
The energy of this flow drives ATP synthase to phosphorylate ADP → ATP (1)

Question 7. (5 marks) Standard theoretical yield = 38 ATP (or 36 accepted).

Glycolysis: 2 ATP (net) + 2 NADH → 6 ATP = 8 ATP... breakdown:
Glycolysis substrate-level: 2 ATP (1)
Link reaction + Krebs substrate-level: 2 ATP (1)
Electron carriers: 10 NADH × 3 = 30 ATP; 2 FADH₂ × 2 = 4 ATP (1 for NADH count, 1 for FADH₂ count)
Total = 2 + 2 + 30 + 4 = 38 ATP (1)

(Accept 36 if 2 ATP used to shuttle cytoplasmic NADH.)

Question 8. (4 marks — ½ each cell, rounded to whole marks)

Feature	Aerobic	Anaerobic
Requires oxygen?	Yes	No
ATP yield per glucose	~38 (36)	2
Final products (animals)	CO₂ + H₂O	Lactic acid
Location	Cytoplasm + mitochondria	Cytoplasm

Award (4) for all correct; deduct for errors.

Question 9. (4 marks) (a) glucose → lactic acid (+ 2 ATP) (2) (b) glucose → ethanol + carbon dioxide (+ 2 ATP) (2)

Question 10. (3 marks)

$NAD^+$ and $FAD$ are coenzymes/electron (and proton) carriers (1)
They are reduced by accepting electrons + H⁺, forming NADH and FADH₂ during glycolysis, link reaction and Krebs cycle (1)
They deliver these electrons to the electron transport chain, where they are re-oxidised back to $NAD^+$ / $FAD$ to be reused (1)

[
  {"claim":"Aerobic respiration balances: C6H12O6 + 6O2 -> 6CO2 + 6H2O (atoms conserved)","code":"C_in=6; H_in=12; O_in=6*1+6*2; C_out=6; H_out=6*2; O_out=6*2+6*1; result = (C_in==C_out) and (H_in==H_out) and (O_in==O_out)"},
  {"claim":"Total theoretical ATP yield = 38","code":"gly=2; krebs_slp=2; nadh=10*3; fadh2=2*2; total=gly+krebs_slp+nadh+fadh2; result = total==38"},
  {"claim":"Glycolysis net ATP = 4 produced - 2 used = 2","code":"result = (4-2)==2"},
  {"claim":"Krebs per turn yields 3 NADH, so 2 turns give 6 NADH","code":"result = (2*3)==6"}
]