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Secondary Biology: Enzymes and Metabolic Reactions (Paper 4)
Secondary Biology: Enzymes and Metabolic Reactions (Paper 4)
Ten original questions working between amount, time and rate, comparing two tubes run for different times, using a ten degree rise to show doubling, explaining why initial rate is used, reading a pH curve and the effect of grinding enzyme into powder.
Direct answer Rate is product divided by time, and comparisons only work once both runs are put on the same time basis.
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)
- FoundationWhich structure inside a cell makes enzymes?
- Foundation90 cm³ of gas is collected in 12 minutes. What is the average rate in cm³/min?
- FoundationAt 15/2 cm³/min, how many minutes are needed to collect 150 cm³?
- FoundationAt about what pH does pepsin work best?
- IntermediateTube A gives 40 cm³ in 8 minutes and tube B gives 15 cm³ in 5 minutes. Which is faster?
- IntermediateRaising the temperature from 20 °C to 30 °C lifts the rate from 4 to 8 cm³/min. How many times faster is it?
- IntermediateWhy is the rate usually measured over the first minute or two rather than averaged over the whole reaction?
- ChallengeAn enzyme is almost inactive at pH 3, fastest at pH 7 and nearly inactive again at pH 11. What does this show?
- ChallengeThe same amount of enzyme is ground from one lump into a fine powder. What happens to the rate, and why?
- Error redoA student collects 20 cm³ in 5 minutes and writes the rate as 20 cm³/min. What is the correct rate?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The ribosome. | Enzymes are proteins, so ribosomes build them to the gene instructions before they are shipped out. |
| 2 | 7.5 cm³/min. | Rate is amount of product divided by time, and the unit cm³/min must be stated. |
| 3 | 20 minutes. | To go from rate back to time, divide the amount of product by the rate and keep the units. |
| 4 | Around pH 2, which is strongly acidic. | Pepsin works in stomach acid, so its optimum pH is far below the neutral 7. |
| 5 | Tube A, at 5.0 cm³/min against 3.0 cm³/min. | Work out each rate per minute before comparing; total volume alone is misleading when times differ. |
| 6 | Twice as fast. | Below the optimum, a rise of about 10 °C roughly doubles the rate because particles collide more often. |
| 7 | Because the substrate falls later on, so a long average underestimates the initial rate. | The initial rate shows what the enzyme can do with plenty of substrate; later readings are limited by substrate. |
| 8 | Enzymes have an optimum pH; moving away lowers activity and extremes can denature them. | pH changes the charges and shape of the active site, which is why the curve is bell-shaped. |
| 9 | It rises, because the larger surface area gives the enzyme more contact with the substrate. | The amount of enzyme is unchanged, but contact area was limiting, so the rate rises while the final yield does not. |
| 10 | 4.0 cm³/min, that is 20 divided by 5. | Quoting the volume as the rate is the commonest unit error; a rate must be divided by time. |
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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