Practise 16 real Federal Board questions on Enzymes from 2023 to 2026. See the answer and explanation as soon as you answer.
Enzymes is one of the 15 main chapters in our Federal Board FSC Biology question bank (11th class), and about 3% of its real questions come from it. Tayyari Karo has 16 real questions on this chapter from 2023 to 2026; 4 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 15 medium, 1 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.
The minimum energy required to start a chemical reaction is called:
Answer: B. Activation energy
Activation energy is the energy barrier that must be overcome for reactant molecules to be converted into products; enzymes work by lowering this barrier.
The compound malonate is a competitive inhibitor of:
Answer: C. Succinic dehydrogenase
Malonate closely resembles succinate in shape and competitively binds the active site of succinate dehydrogenase, blocking the Krebs-cycle conversion of succinate to fumarate.
Which model explains enzyme action by showing a change in the active site to fit the substrate?
Answer: B. Induced Fit Model
The induced fit model proposes the active site is flexible and changes shape as the substrate binds, improving the fit; the lock-and-key model assumes a rigid, pre-fitting active site.
They catalyze the breakdown of specific covalent bonds and removal of groups without hydrolysis:
Answer: A. Lyases
Lyases break bonds (e.g. C–C, C–O) and remove groups non-hydrolytically, often forming a double bond or ring.
Classify enzymes on the basis of the substrates they act upon, giving any three examples.
(1) Carbohydrases — act on carbohydrate substrates, e.g. amylase (breaks down starch).
(2) Proteases — act on protein substrates, e.g. pepsin (breaks down proteins in the stomach).
(3) Lipases — act on lipid substrates, e.g. lipase (breaks down fats into fatty acids and glycerol).
Compare the characteristics of cofactors of enzymes with one example of each.
TypeCharacteristicExampleInorganic cofactorA metal ion required for enzyme activity/stabilising its structureZn²⁺ (in carbonic anhydrase)CoenzymeAn organic, loosely-bound cofactor, often derived from a vitamin, that carries chemical groups between reactionsNAD⁺ (in dehydrogenases)Prosthetic groupAn organic cofactor tightly/permanently bound to the enzymeHeme group (in catalase)
What are the three types of cofactors? Give one example of each.
(1) Inorganic ion (metal) cofactor — a metal ion needed for activity, e.g. Zn²⁺ in carbonic anhydrase.
(2) Coenzyme — a loosely-bound organic molecule (often vitamin-derived) that carries chemical groups between reactions, e.g. NAD⁺.
(3) Prosthetic group — an organic cofactor tightly/permanently bound to the enzyme, e.g. the heme group in catalase.
Briefly explain importance of competitive inhibitors.
Competitive inhibitors are molecules structurally similar to the normal substrate that compete with it for binding to the enzyme's active site, reducing reaction rate (an effect that can be overcome by increasing substrate concentration). Their importance: (1) they help regulate metabolic pathways (e.g. end-product/feedback inhibition controlling flux through a pathway); (2) they are exploited in drug design — many medicines (e.g. some antibiotics, statins) work as competitive inhibitors of specific target enzymes; (3) studying them helps researchers understand enzyme active-site structure and specificity.
| Session | Questions |
|---|---|
| 2026 Annual | 3 |
| 2025 1st Annual | 4 |
| 2025 2nd Annual | 4 |
| 2024 Annual | 3 |
| 2023 Annual | 2 |
16 real Federal Board (FBISE) Biology questions on Enzymes from 2023 to 2026, for 11th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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