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Secondary Biology: Enzymes and Metabolic Reactions (Paper 3)
Secondary Biology: Enzymes and Metabolic Reactions (Paper 3)
Ten original questions on active sites, converting rate to time, spotting the limiting factor, heavy metal inhibition, and telling reversible cold inactivation apart from permanent heat denaturation.
Direct answer Rate is product divided by time, and only heat or extreme pH denatures an enzyme for good.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: Secondary Biology: Enzymes and Metabolic Reactions |
| Level | 4 basic, 3 advanced, 2 challenge and 1 redo question |
02 Questions (10 items)
- FoundationWhat is the part of an enzyme where the substrate binds called?
- FoundationAn enzyme produces 4 cm³ of gas each minute. How long is needed to collect 32 cm³?
- FoundationAn enzyme is frozen at -18 °C. Can it work again after thawing, and why?
- FoundationWhy does an enzyme not work again after boiling and cooling back to 37 °C?
- IntermediateTube A gives 18 cm³ in 6 minutes; tube B gives 27 cm³ in 9 minutes. Are the rates equal, and how long would 45 cm³ take?
- IntermediateSubstrate concentration keeps rising but the rate levels off. Why?
- IntermediateAdding more enzyme raises the rate from 3.0 to 6.0 cm³ per minute. What does this show?
- ChallengeHeavy metal ions make an enzyme lose its activity. What is a likely mechanism?
- ChallengeGive two features of enzymes that differ from inorganic catalysts.
- Error redoA pupil says putting an enzyme in a fridge denatures it permanently. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The active site. | The active site is complementary in shape to the substrate, which makes enzymes specific. |
| 2 | 8 minutes (32 divided by 4). | Time equals the total amount divided by the rate. |
| 3 | Yes. Low temperature only slows the molecules and lowers activity; the protein structure is not destroyed. | Cold slows an enzyme down, whereas heat destroys its shape. |
| 4 | Heat denatures the protein, so the shape of the active site is permanently changed. | Denaturation is irreversible, and cooling cannot restore the shape. |
| 5 | Yes, both are 3.0 cm³ per minute, so 45 cm³ needs 15 minutes. | Work out each rate before comparing; do not compare totals alone. |
| 6 | All the active sites are already occupied, so the amount of enzyme becomes the limiting factor. | The limiting factor is whichever requirement runs out first. |
| 7 | The rate doubles, so the amount of enzyme was the limiting factor. | If extra enzyme helps, substrate was still available. |
| 8 | The ions bind to the enzyme and change the shape of the active site, so the substrate can no longer fit. | Once the active site changes shape, specific binding fails. |
| 9 | They are specific to particular substrates and work efficiently at mild temperatures and pH. | Being proteins, enzymes cannot tolerate extreme heat or strong acid and alkali. |
| 10 | Cold only lowers activity without destroying the structure, so warming restores it; permanent denaturation needs heat or extreme pH. | Refrigeration is not denaturation; keep the two ideas separate. |
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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