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DSE Biology | Enzymes and Factors Practice Paper 2 (Definitions and Temperature Curves)
DSE Biology | Enzymes and Factors Practice Paper 2 (Definitions and Temperature Curves)
From what an enzyme is and the lock-and-key model, through Q10 and percentage falls on one data set, to cofactors and immobilised enzymes.
Attempt first, mark afterwards Allow about thirty minutes; for each temperature item decide where the optimum lies before choosing Q10 or denaturation.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 items |
| Suggested time | About 30 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: DSE Biology | Enzymes and Affecting Factors |
| Level | S4 (Secondary 4) Biology |
02 Questions (10 items)
- FoundationWhat is an enzyme made of, and does it supply energy or a pathway?
- FoundationUnder the lock-and-key model, can amylase break down protein? Why?
- FoundationOne enzyme gives 12 mg/min at 20°C, 24 at 30°C, 30 at 40°C and 9 at 50°C. Find Q10 for 20-30°C, Q10 for 30-40°C and the fall from 40 to 50°C.
- Foundation45 cm3 of gas is collected in 15 minutes. What is the average rate, and how long would 60 cm3 take at that rate?
- IntermediateWith plenty of substrate, doubling the enzyme lifts the rate from 20 to 40. With limited substrate the same doubling only lifts it from 20 to 26. What limits each case?
- IntermediateA heavy metal acts as a non-competitive inhibitor, cutting Vmax from 100 to 50 while Km stays at 8. At substrate 24, what is the rate before and after, and can extra substrate restore it?
- IntermediateWithout zinc, carboxypeptidase keeps only 15% of its normal activity. How many percentage points are lost, and what role does zinc play?
- ChallengeAn enzyme runs at 6.0 units at 10°C and 26.4 units at 30°C. What is the average Q10 across those 20 degrees?
- ChallengeFree lactase keeps only 82% of its previous activity after each reuse. How much is left after five runs, and what does immobilised lactase (still 82% after ten runs) show?
- Error redoError drill: a student writes that enzymes supply energy so that otherwise impossible reactions happen. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Mostly globular protein (a few are RNA); it supplies a lower-activation-energy pathway, not energy | An enzyme does not hand out energy. It lowers the activation energy so more molecules can clear the barrier at body temperature. |
| 2 | No; its active site is complementary only to starch and its breakdown products | Specificity comes from the shape of the active site, so a mismatched substrate cannot form an enzyme-substrate complex. |
| 3 | Q10 = 2.0 and 1.25; a fall of 70.0% from 40 to 50°C | 24 over 12 = 2.0 and 30 over 24 = 1.25; past the optimum at 50°C denaturation sets in, so the rate drops from 30 to 9, which is 70.0%. |
| 4 | 3.0 cm3 per minute; 20 minutes | 45 over 15 = 3.0, so 60 divided by 3.0 gives 20 minutes. |
| 5 | The first is limited by enzyme amount (2.0 times); the second by substrate (only 30.0%) | When substrate is plentiful the rate is proportional to enzyme amount; when it is scarce the extra active sites simply sit idle. |
| 6 | From 75.0 to 37.5, a fall of 50.0%; extra substrate cannot restore it | 100×24 over 32 = 75.0 and 50×24 over 32 = 37.5; the active site itself is distorted, so more substrate cannot compensate. |
| 7 | It loses 85.0 percentage points; zinc is a cofactor | 100% minus 15% = 85.0 points; the inorganic ion binds the enzyme and shapes a working active site. |
| 8 | 2.1 (the square root of 4.4) | 26.4 over 6.0 = 4.3999999999999995 across two 10-degree steps, so Q10 is the square root of 4.3999999999999995, about 2.1. |
| 9 | About 37.1% left for the free enzyme; immobilisation allows easy recovery and gives higher stability | 0.82 to the fifth power is 0.3707, so about 37.1%; immobilising the enzyme on a support reduces denaturation and washout. |
| 10 | Enzymes only lower activation energy and speed up reaching equilibrium; they supply no energy and do not shift the equilibrium | Energy comes from the surroundings, for example body heat; the enzyme changes the energy barrier of the pathway, not the free-energy change or the final yield. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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