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IB Biology: Photosynthesis and Limiting Factors (Paper 2: intermediate)
IB Biology: Photosynthesis and Limiting Factors (Paper 2: intermediate)
IB biology photosynthesis paper two, intermediate: absorption spectra, chromatography Rf, the DCPIP experiment, the compensation point and Q10.
Direct answers Answers in order: red and blue violet, 0.35, DCPIP is reduced, 4 times, 50 per cent, 3.8 g, the light compensation point, light intensity or temperature, Q10 of 2, and respiration runs day and night.
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)
- FoundationWhich two regions of the spectrum does chlorophyll a absorb most strongly?
- FoundationA pigment travels 4.2 cm while the solvent front travels 12 cm. What is its Rf value?
- FoundationDCPIP turns from blue to colourless in a light reaction experiment. What does this show?
- IntermediateTubes at light intensities 10, 20 and 40 units decolourise in 120, 60 and 30 seconds. How many times faster is the fastest than the slowest?
- IntermediateWarming from 25 C to 35 C raises the rate from 12 to 18. What is the percentage increase?
- IntermediateOver 24 hours a plant fixes 0.8 g per hour during 10 hours of light and loses 0.3 g per hour during 14 hours of darkness. What is the daily net?
- ChallengeWhat does the point where the photosynthesis curve meets the respiration line represent?
- ChallengeRaising greenhouse carbon dioxide from 0.04 to 0.1 per cent lifts the rate from 8 to 14, but further enrichment changes nothing. What limits the rate now?
- ChallengeA rise from 25 C to 35 C takes the rate from 6 to 12. What is the Q10?
- Error redoA student claims plants do not respire in the dark. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Red and blue violet light | Green light is mostly reflected or transmitted, which is why leaves look green. |
| 2 | 0.35 | Rf is 4.2 divided by 12, which is 0.35. |
| 3 | DCPIP is being reduced | Electrons from the light reactions reduce DCPIP, so the rate of fading reflects the rate of the light reactions. |
| 4 | 4 times | The times are in the ratio 4 to 1, so the rates are in the ratio 1 to 4. |
| 5 | 50 per cent | Six divided by 12, times 100, gives 50. |
| 6 | 3.8 g | Ten times 0.8 is 8 and fourteen times 0.3 is 4.2, so the difference is 3.8. |
| 7 | The light compensation point | At that light intensity gross photosynthesis equals respiration, so net gas exchange is zero. |
| 8 | Light intensity or temperature | Carbon dioxide is near saturation, so another factor has taken over as the limit. |
| 9 | 2 | Q10 is 12 divided by 6, so the rate doubles for each 10 C rise. |
| 10 | Respiration runs day and night, in darkness there is respiration but no photosynthesis | Respiration is continuous cell activity while photosynthesis only happens in the light. |
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 →
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