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IB Biology: Photosynthesis and Limiting Factors (Paper 1: basics)
IB Biology: Photosynthesis and Limiting Factors (Paper 1: basics)
IB biology photosynthesis paper one, basics: from equation ratios and the site of the light reactions to net photosynthesis and first limiting factor calculations.
Direct answers Answers in order: 6, the thylakoid membrane, oxygen, 0.075 cm3, 80 per cent, 0.06 g, 14 units, carbon dioxide concentration, 3.6 g, and the light reactions do not make glucose directly.
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)
- FoundationHow many carbon dioxide molecules are needed to make one glucose molecule in photosynthesis?
- FoundationWhere in the chloroplast do the light reactions take place?
- FoundationWhich gas is released when water is split in the light reactions?
- IntermediateFour leaves release 12 cm3 of oxygen in 40 minutes. What is the average release per leaf per minute?
- IntermediateRaising light intensity from 20 to 40 units lifts the rate from 5 to 9 arbitrary units. What is the percentage increase?
- IntermediateA leaf fixes 0.36 g of carbon dioxide over six hours of light. What is the mean rate per hour?
- ChallengeA leaf has a gross photosynthetic rate of 18 units and a respiration rate of 4 units. What is the net rate?
- ChallengeDoubling light lifts the rate only from 6 to 7.5, yet raising carbon dioxide lifts it sharply. Which factor was limiting?
- ChallengeA leaf fixes 0.5 g per hour in 12 hours of light and loses 0.2 g per hour in 12 hours of darkness. What is the daily net fixation?
- Error redoA student says the light reactions make glucose directly. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 6 | The equation 6CO2 + 6H2O gives C6H12O6 + 6O2, a ratio of six to one. |
| 2 | On the thylakoid membrane | The photosystems, electron transport chain and ATP synthase are all embedded in the thylakoid membrane. |
| 3 | Oxygen | Photolysis of 2H2O gives 4H+, 4e- and O2, so the oxygen comes from water. |
| 4 | 0.075 cm3 | 12 divided by the product of 4 and 40 gives 0.075. |
| 5 | 80 per cent | The rise of 4 divided by 5, times 100, gives 80. |
| 6 | 0.06 g | 0.36 divided by 6 gives 0.06. |
| 7 | 14 units | Net equals gross minus respiration, so 18 minus 4 gives 14. |
| 8 | Carbon dioxide concentration | Extra light gave little gain while extra carbon dioxide gave a large one, so carbon dioxide was limiting. |
| 9 | 3.6 g | Twelve times 0.5 is 6 and twelve times 0.2 is 2.4, so the difference is 3.6. |
| 10 | The light reactions only make ATP and NADPH, glucose is built in the Calvin cycle from fixed carbon dioxide | The light reactions supply energy and reducing power, while carbon fixation happens in the Calvin cycle in the stroma. |
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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