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S1 Science: Plants and Photosynthesis (Paper 3 (challenge))
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Tutor Prep Guide · Photosynthesis inputs and outputs, leaf structure, stomata and transpiration, and the iodine starch test
S1 Science: Plants and Photosynthesis (Paper 3 (challenge))
This paper deals with net effect, the compensation point and limiting factors, with mass and percentage calculations.
Direct answers Photosynthesis and respiration run together, so the net effect is what can be observed.
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: S1 Science: Plants and Photosynthesis |
| Level | S1 |
02 Questions (10 items)
- FoundationIn daylight, do photosynthesis and respiration happen at the same time?
- FoundationWhat is the compensation point of photosynthesis?
- FoundationLight is already high and raising it further gives no more oxygen, but raising carbon dioxide does. What is the limiting factor?
- IntermediateWhy does the rate of photosynthesis fall above about 40 C?
- Intermediate264 g of carbon dioxide (molar mass 44 g) is used completely. What mass of glucose (molar mass 180 g) forms?
- IntermediateA plant fixes 3 g of carbon dioxide per hour for 10 hours, while respiration releases 6 g in the day. What is the net fixation?
- ChallengeGreenhouse carbon dioxide rises from 0.04 to 0.10 percent. What is the relative increase?
- ChallengeStomata open by day and close at night. When is transpiration stronger and why?
- ChallengeLeaves are arranged on the stem so that they overlap as little as possible. How does this help photosynthesis?
- Error redoA student says photosynthesis only happens by day, so plants do not respire in daytime. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Yes, both run together and the net effect depends on their rates | Photosynthesis needs light while respiration never stops, so the two overlap by day. |
| 2 | The light intensity at which the rate of photosynthesis equals the rate of respiration | At that point the plant neither releases nor takes in oxygen overall. |
| 3 | Carbon dioxide concentration | Whichever factor raises the rate when increased is the limiting factor at that moment. |
| 4 | The enzymes involved are denatured, so the reactions slow down | High temperature destroys the shape of the enzymes and the activity cannot be restored. |
| 5 | 180 g | Dividing 264 by 44 gives 6 mol, which make 1 mol of glucose, that is 180 g. |
| 6 | 24 g | Three grams times ten is 30 g, and taking away the 6 g from respiration leaves 24 g. |
| 7 | A relative increase of 150 percent | The difference divided by the original gives 1.50, so the relative rise is 150 percent while the absolute rise is 0.06 percentage points. |
| 8 | By day, because the stomata are open and the temperature is higher | Once the stomata close, water vapour can hardly escape and transpiration falls sharply. |
| 9 | Less shading between leaves means each leaf receives more light | More exposed leaf area means a larger total rate for the whole plant. |
| 10 | Respiration never stops; by day photosynthesis simply runs faster | In the day the photosynthetic rate exceeds the respiratory rate, giving a net release of oxygen. |
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.
For photosynthesis questions ask three things: whether all inputs are present (light, carbon dioxide, water), what the outputs are, and which condition the experiment changed.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.