This free quiz has 17 multiple choice questions on respiration, all taken from OCR A Level Biology A exam papers. It marks itself, so you get your score as soon as you finish.
What the quiz covers (OCR A spec 5.2.2)
Mitochondrial structure, mitochondrial DNA and the endosymbiotic origin of mitochondria
Glycolysis and the link reaction
The Krebs cycle and its products
Coenzymes NAD, FAD and coenzyme A
Oxidative phosphorylation and chemiosmosis, compared with photosynthesis
Anaerobic respiration and ATP yield, including in red blood cells
Energy values of carbohydrates, lipids and proteins
Respiratory quotients and using a respirometer
How to use it
Before you start, sketch a quick flow chart of glycolysis, the link reaction, the Krebs cycle and the electron transport chain, and note where in the cell each happens and where carbon dioxide, reduced NAD, reduced FAD and ATP appear. For RQ questions, write RQ = CO2 produced ÷ O2 used at the top of your page and work from the equation given.
Where students lose marks (from OCR examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Not all phosphorylation is substrate-level: Many students called the phosphorylation of fructose phosphate in early glycolysis 'substrate-level phosphorylation', and were often unsure how many ATP the Krebs cycle makes or where in the cycle this happens.
✔ Gains credit: Describing the early step simply as phosphorylation using ATP, and keeping substrate-level phosphorylation for ATP made directly in glycolysis (4 ATP made, 2 used, net 2 per glucose, when triose phosphate is converted to pyruvate) and in the Krebs cycle (one ATP per turn, so two per glucose).
Decarboxylation, not hydrolysis: Hydrolysis was a common wrong name for the reaction that releases carbon dioxide, and some students placed carbon dioxide release in glycolysis or oxidative phosphorylation.
✔ Gains credit: Naming the reaction as (oxidative) decarboxylation, and stating that carbon dioxide is released in the link reaction and the Krebs cycle.
Coenzymes accept hydrogen atoms: Many students wrote that NAD or FAD simply 'remove' hydrogen, or referred to hydrogen ions or hydrogen molecules, and some explained oxidation in glycolysis only as a loss of electrons.
✔ Gains credit: Stating that hydrogen atoms are removed from the substrate (dehydrogenation) and that NAD or FAD accepts, carries or is reduced by these hydrogen atoms.
Where FAD is reduced and oxidised: The most common error was placing the release of hydrogen from reduced FAD in the intermembrane space, and few students realised that NAD and FAD do not oxidise molecules in the electron transport chain.
✔ Gains credit: Placing the reduction of FAD in the mitochondrial matrix and its oxidation at the inner mitochondrial membrane, with reduced NAD and reduced FAD described as reducing (passing hydrogen to) the electron transport chain.
ATP does not pump protons: A common misconception was that ATP provides the energy to move protons into the intermembrane space, and some students described protons being pumped through ATP synthase or 'energy produced' to make ATP.
✔ Gains credit: Protons pumped into the intermembrane space using energy from electrons in the electron transport chain, then diffusing down their concentration gradient back into the matrix through ATP synthase, providing energy to join ADP and Pi.
End-product inhibition, named and explained: Some students called the inhibition of PFK by later products 'end point inhibition' or just 'negative feedback', or stated that ATP is a non-competitive inhibitor instead of explaining why it cannot be a competitive one. Others wrote about ATP being needed for energy instead of the rate of glycolysis.
✔ Gains credit: The term end-product inhibition, explaining that ATP is not similar in shape to the substrate so is not complementary to the active site, and linking a high ATP to AMP ratio to a lower rate of glycolysis.
Counting carbons into the Krebs cycle: Many students did not read what was being calculated, giving 100% for complete oxidation of a fatty acid or dividing an arbitrary number by the carbon total, and the efficiency of the link reaction was often wrong or wrongly rounded.
✔ Gains credit: Tracking carbon atoms, so that only the 2 carbons of each acetyl group passed on count, for example 2 out of 3 carbons from pyruvate in the link reaction (67%), rounded correctly.
Keep practising
Go on to the Photosynthesis quiz, the Enzymes quiz or the Ecosystems and Populations quiz, or browse all our OCR A Level Biology quizzes. Our OCR A masterclasses (Year 12 on Wednesdays at 5.15pm, Year 13 on Tuesdays at 6.30pm) work through real exam questions on one topic each week.