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IB Biology: Photosynthesis and Limiting Factors (Paper 4: mistake clinic)
IB Biology: Photosynthesis and Limiting Factors (Paper 4: mistake clinic)
IB biology photosynthesis paper four, mistake clinic: ten questions fixing site confusion, wrong products, unit conversion and the optimum temperature.
Direct answers Answers in order: membrane and stroma, ATP and NADPH, 6, 16 units, 0.6, 30 cm3 per hour, light near saturation, 5.9 g, 180 g/mol, and enzymes denature above the optimum.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: IB Biology: Photosynthesis and Limiting Factors |
| Level | IB |
02 Questions (10 items)
- FoundationWhere do the light reactions and the Calvin cycle take place in the chloroplast?
- FoundationWhat are the two main products of the light reactions?
- FoundationHow many carbon dioxide molecules must be fixed to build one glucose molecule?
- IntermediateGross photosynthesis is 22 units and respiration 6 units. What is the net rate?
- IntermediateA pigment moves 5.4 cm while the solvent front moves 9 cm. What is the Rf value?
- IntermediateA rate of 0.5 cm3 per minute is how many cm3 per hour?
- ChallengeThe rate is 10 at 40 units of light, 12 at 60 and 12.5 at 80. What does the flattening show?
- ChallengeA leaf fixes 0.6 g per hour over 14 hours of light and loses 0.25 g per hour over 10 hours of darkness. What is the daily net?
- ChallengeWhat is the molar mass of one glucose molecule in g/mol, taking C 12, H 1 and O 16?
- Error redoA student claims the higher the temperature the faster photosynthesis always is. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The light reactions on the thylakoid membrane and the Calvin cycle in the stroma | Knowing membrane versus stroma is where marks are usually lost. |
| 2 | ATP and NADPH | Both feed the Calvin cycle, and glucose is not a product of the light reactions. |
| 3 | 6 | The equation ratio is six to one, and six carbons make one glucose. |
| 4 | 16 units | Net is 22 minus 6, which is 16. |
| 5 | 0.6 | 5.4 divided by 9 gives 0.6. |
| 6 | 30 cm3 per hour | Half a cubic centimetre times 60 gives 30, so multiply by the minutes in an hour. |
| 7 | Light is near saturation and carbon dioxide or temperature now limits the rate | Extra light brings diminishing returns because another factor has taken over. |
| 8 | 5.9 g | Fourteen times 0.6 is 8.4 and ten times 0.25 is 2.5, so the difference is 5.9. |
| 9 | 180 g/mol | Six times 12 plus twelve times 1 plus six times 16 gives 180. |
| 10 | Above the optimum the enzymes denature and the rate falls | Photosynthesis is enzyme controlled, so it has an optimum and overheating denatures the enzymes. |
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.
The light reactions make ATP and NADPH in the thylakoid membrane while the Calvin cycle fixes carbon dioxide in the stroma, and the slowest of light, carbon dioxide and temperature sets the overall rate.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.