OCR A 2.1.4 · 20 written questions · 38 marks · about 45 minutes · marked as you go
This free quiz has 20 written exam questions on enzymes, all taken from OCR A Level Biology A papers (AS and A level, 2018 to 2025). Short answers and calculations mark themselves. For longer answers you write your answer, then tick off the OCR mark-scheme points you made, so you see exactly where the marks are. This quiz covers the whole of OCR A 2.1.4: what enzymes do in metabolism, intracellular and extracellular enzymes, how enzymes work, the factors that affect their activity (with Q₁₀ calculations and practical work), cofactors and coenzymes, and inhibitors.
What the quiz covers (OCR A spec 2.1.4)
Enzymes in metabolism (2.1.4(a)(b)): intracellular and extracellular enzymes, including catalase
Mechanism of enzyme action (2.1.4(c)): the induced-fit hypothesis and how enzymes lower activation energy
Factors affecting enzyme activity (2.1.4(d)(i)): substrate concentration, temperature, pH and the temperature coefficient (Q₁₀)
Practical investigations (2.1.4(d)(ii)): finding an initial rate from a graph, calculating Q₁₀ and controlling pH
Cofactors and coenzymes (2.1.4(e)): vitamins as coenzymes and Ca²⁺ as a cofactor
Inhibitors (2.1.4(f)): competitive and non-competitive, reversible and non-reversible inhibition, and end-product inhibition
How to use it
Write every answer in full, as you would in the exam: the mark for each question is shown, so you know how much to write. When you self-mark, only tick a point if your answer clearly makes it, then read the examiner's tip under each question. Your progress is saved on your device, so you can do it in two sittings, and at the end you can retry just the questions where you dropped marks.
Prefer multiple choice? Try the 20-question Enzymes multiple choice quiz first.
Open the Enzymes quiz in a new tab (easier on a phone)
Where students lose marks (from OCR examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Rate plateaus, it doesn't fall: At high substrate concentration, some students said the rate of reaction decreases or slows down. OCR did not allow this.
✔ Gains credit: All the active sites become occupied, so the rate levels off (Vmax is reached) and enzyme concentration becomes the limiting factor.
Read the graph before saying 'optimum': Asked to explain temperature curves, most students wrote that 37 °C is the optimum where enzymes 'work best', ignoring a graph that showed a faster initial rate at 60 °C.
✔ Gains credit: At 60 °C there is more kinetic energy, so more enzyme-substrate complexes form and the initial rate is faster, but the enzyme is denatured so the reaction stops earlier.
Induced fit means a shape change: Many students named 'lock and key' when the stem described the active site changing shape around the substrate.
✔ Gains credit: Induced fit: the active site changes shape as the substrate binds.
Say how activation energy is lowered: Students stated that enzymes lower the activation energy but couldn't explain how, or just restated the question.
✔ Gains credit: The change to the active site puts the bonds in the substrate under strain, so they break more easily and the activation energy is lower.
Initial rate needs a tangent at the start: Many students couldn't draw a tangent in the right part of the curve to find the initial rate, and didn't give the answer to the requested significant figures.
✔ Gains credit: Draw a tangent at the very start of the curve, then gradient = change in y ÷ change in x, given to the number of significant figures asked for.
Ca²⁺ is a cofactor: The inorganic Ca²⁺ ion was often called a coenzyme or a prosthetic group, which was not credited.
✔ Gains credit: Ca²⁺ is a cofactor: an inorganic ion needed for the enzyme to work (coenzymes are organic, often from vitamins).
Coenzymes bind only temporarily: Few students said that coenzymes assist enzymes without being permanently bound, and some said they bind permanently.
✔ Gains credit: Coenzymes assist enzymes by binding temporarily, e.g. helping the substrate bind to the active site.
End-product, not end point: Students wrote 'end point inhibition', 'negative feedback' or 'homeostasis' for inhibition by a product at the end of a pathway.
✔ Gains credit: End-product inhibition: the final product of the pathway inhibits an enzyme earlier in it.
Keep practising
Try the Enzymes multiple choice quiz, the Biological Molecules quiz, the Nucleotides, DNA and Protein Synthesis written quiz or the Biological Membranes written 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.
Questions, mark schemes and examiners' report extracts © OCR.