Practise 36 real questions on Enzymes and biological molecules from 2021 to 2026. See the answer and explanation as soon as you answer.
Enzymes and biological molecules is one of the 13 main topics in our O Level Biology (Cambridge (CAIE) 5090) question bank, and about 6% of its real questions come from it. Tayyari Karo has 36 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4; 21 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 29 medium, 4 hard, 3 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Many nutrients can be identified by simple chemical tests. Which nutrient causes Benedict's solution to change colour to red?
Answer: C. glucose
Benedict's solution turns from blue to orange-red when heated with a reducing sugar such as glucose.
Which row does not correctly link an enzyme with its substrate and an end-product? (A starch, amylase, maltose; B lipid, lipase, fatty acids; C protein, protease, amino acids; D starch, amylase, glycerol)
Answer: D. substrate starch, enzyme amylase, end-product glycerol
Amylase breaks starch down to maltose, not glycerol; glycerol comes from lipid digestion.
Which statement about enzymes is not correct?
Answer: D. They have active sites the same shape as their substrate molecules.
Enzymes are biological catalysts. Which type of molecule can be an enzyme?
Answer: D. protein
Enzymes are proteins.
A liquid turned red with Benedict's solution (heated) and mauve (purple) with biuret reagent. Which conclusion is correct?
Answer: D. The liquid contained glucose and protein.
Which statements are correct? 1 Enzymes are proteins and function as catalysts. 2 Enzymes are changed by the reaction they catalyse. 3 The lock and key hypothesis explains the way enzymes function.
Answer: C. 1 and 3 only
(a) Explain the lock and key hypothesis of enzyme action using a named example. [5] (b) Explain, using examples, why proteins are essential for all living organisms. [5]
(a) Enzymes are proteins that act as biological catalysts; the lock and key hypothesis states each enzyme has a specific active site (the 'lock') shaped to fit only one substrate (the 'key'); e.g. amylase fits starch and breaks it into maltose; the enzyme is not used up; it lowers activation energy and speeds up the reaction. (b) Proteins are needed for: enzymes (catalysis); structural parts (e.g. muscle actin/myosin, collagen); haemoglobin transports oxygen; antibodies for immunity; hormones (e.g. insulin); membranes. They are essential for growth, repair and control.
Best-effort; mark scheme not parsed.
| Session | Paper 1 | Paper 2 | Paper 3 | Paper 4 |
|---|---|---|---|---|
| May/June 2026 | 2 | 1 | – | 1 |
| May/June 2025 | 3 | 1 | 1 | – |
| Oct/Nov 2025 | 2 | 1 | 1 | 1 |
| May/June 2024 | 1 | – | – | – |
| Oct/Nov 2024 | 2 | 1 | – | – |
| May/June 2023 | 1 | – | – | – |
| Oct/Nov 2023 | 3 | – | 1 | 1 |
| May/June 2022 | 2 | 1 | – | – |
| Oct/Nov 2022 | 2 | 1 | 1 | 1 |
| May/June 2021 | 2 | – | – | – |
| Oct/Nov 2021 | 1 | 1 | – | – |
36 real O Level Biology (5090) questions on Enzymes and biological molecules from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4. Each one shows the year, session and paper it came from.
Yes. Every question shows the correct answer and a short explanation the moment you answer.
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