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A Level H1 Biology Plant Biology Quiz
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Questions
A-Level Biology H1 Quiz – Plant Biology
Name: ______________________
Class: ______________________
Date: ______________________
Score: ____ / 80
Duration: 1 hour 15 minutes
Total Marks: 80
Instructions:
- Answer all questions in the spaces provided.
- Write your answers clearly and concisely.
- Marks are allocated for scientific accuracy and clarity of expression.
- Use diagrams where appropriate.
Section A: Short Answer and Structured Questions (20 marks)
1. State the overall equation for photosynthesis. [2 marks]
2. Describe the arrangement of thylakoid membranes within a chloroplast. [3 marks]
3. Explain why the light-dependent reactions of photosynthesis cannot occur in the dark. [3 marks]
4. Identify two products of the light-dependent reactions that are used in the light-independent reactions. [2 marks]
5. With reference to the absorption spectrum of chlorophyll, explain why plants appear green. [4 marks]
6. Define photolysis and state its significance in photosynthesis. [3 marks]
7. Explain how temperature affects the rate of photosynthesis. [3 marks]
Section B: Diagram and Data Interpretation (30 marks)
8. Figure 1 shows a diagram of a chloroplast.
(a) Label the parts A, B, and C. [3 marks]
A: ________________
B: ________________
C: ________________
(b) State the location of the light-dependent reactions. [1 mark]
(c) Explain the role of part C in the light-independent reactions. [2 marks]
9. Figure 2 shows the absorption spectrum of chlorophyll a and chlorophyll b.
(a) With reference to Figure 2, state the wavelengths of light absorbed most strongly by chlorophyll a. [2 marks]
(b) Explain why chlorophyll appears green based on the absorption spectrum. [3 marks]
10. Table 1 shows the rate of photosynthesis of a plant under different light intensities.
| Light Intensity (lux) | Rate of Photosynthesis (cm³ CO₂ m⁻² s⁻¹) |
|---|---|
| 0 | 0 |
| 200 | 1.2 |
| 400 | 2.4 |
| 600 | 3.6 |
| 800 | 4.2 |
| 1000 | 4.5 |
| 1200 | 4.5 |
(a) Using the data, describe the relationship between light intensity and the rate of photosynthesis. [2 marks]
(b) Explain the shape of the curve with reference to limiting factors. [3 marks]
11. Figure 3 shows the electron transport chain in the thylakoid membrane.
(a) With reference to Figure 3, describe the flow of electrons from photosystem II to photosystem I. [4 marks]
(b) Explain how the electron flow leads to ATP synthesis. [4 marks]
12. Table 2 shows the effect of carbon dioxide concentration on the rate of photosynthesis of two plant species, X and Y.
| CO₂ Concentration (ppm) | Rate for Species X (cm³ O₂ m⁻² s⁻¹) | Rate for Species Y (cm³ O₂ m⁻² s⁻¹) |
|---|---|---|
| 100 | 0.5 | 0.3 |
| 200 | 1.0 | 0.6 |
| 300 | 1.5 | 1.2 |
| 400 | 2.0 | 1.8 |
| 500 | 2.0 | 2.4 |
(a) Compare the response of Species X and Species Y to increasing CO₂ concentration. [2 marks]
(b) Suggest a reason for the difference in the response of Species Y at high CO₂ concentration. [2 marks]
Section C: Extended Response (30 marks)
13. Describe how light energy is converted into chemical energy in the form of ATP during the light-dependent reactions of photosynthesis. [8 marks]
14. Explain the role of NADP in photosynthesis and describe how it is reduced. [4 marks]
15. Compare cyclic and non-cyclic photophosphorylation. [6 marks]
16. Discuss how plants adapted to arid conditions carry out photosynthesis efficiently. [6 marks]
17. With reference to the structure of a leaf, explain how it is adapted for photosynthesis. [6 marks]
18. An experiment was conducted to measure the rate of photosynthesis using an aquatic plant. The number of oxygen bubbles produced per minute was counted under different conditions. The results are shown in Table 3.
| Condition | Bubbles per Minute |
|---|---|
| Low light, 25°C | 5 |
| High light, 25°C | 25 |
| High light, 35°C | 30 |
| High light, 35°C, extra CO₂ | 45 |
(a) Calculate the percentage increase in the rate of photosynthesis from low light to high light at 25°C. [2 marks]
(b) Explain the effect of increasing temperature from 25°C to 35°C on the rate of photosynthesis. [3 marks]
(c) Suggest why adding extra CO₂ increased the rate of photosynthesis. [2 marks]
19. Discuss the significance of photosynthesis in maintaining the balance of atmospheric oxygen and carbon dioxide. [5 marks]
20. A student investigated the effect of light wavelength on photosynthesis using colored filters. The results are shown in Table 4.
| Filter Color | Rate of Photosynthesis (cm³ O₂ m⁻² s⁻¹) |
|---|---|
| Blue | 4.5 |
| Green | 1.0 |
| Red | 4.0 |
| Yellow | 2.5 |
(a) With reference to the absorption spectrum of chlorophyll, explain the results for blue and green light. [4 marks]
(b) Predict the rate of photosynthesis under white light and explain your reasoning. [2 marks]
End of Quiz
Answers
A-Level Biology H1 Quiz – Plant Biology – Answer Key
Section A: Short Answer and Structured Questions
1. State the overall equation for photosynthesis. [2 marks]
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(Accept: 1 mark for correct reactants; 1 mark for correct products. Light and chlorophyll not required for 2 marks but expected.)
2. Describe the arrangement of thylakoid membranes within a chloroplast. [3 marks]
- Thylakoids are flattened membrane-bound sacs (1)
- Thylakoids stack to form grana (1)
- Grana are interconnected by stroma lamellae (1)
3. Explain why the light-dependent reactions of photosynthesis cannot occur in the dark. [3 marks]
- Light energy is essential for exciting electrons in chlorophyll (1)
- Without light, photolysis of water cannot occur (electrons not replaced) (1)
- Electron transport chain and ATP synthesis require light-driven electron flow (1)
4. Identify two products of the light-dependent reactions that are used in the light-independent reactions. [2 marks]
- ATP (1)
- Reduced NADP (NADPH) (1)
5. With reference to the absorption spectrum of chlorophyll, explain why plants appear green. [4 marks]
- Chlorophyll absorbs light mostly in the blue and red regions of the spectrum (1)
- Chlorophyll absorbs green light poorly (reflects/transmits green light) (1)
- The green light reaches the eye (1)
- Therefore, plants appear green (1)
6. Define photolysis and state its significance in photosynthesis. [3 marks]
- Photolysis is the splitting of water using light energy (1)
- Significance: replaces electrons lost by chlorophyll (1), produces oxygen as a by-product (1)
7. Explain how temperature affects the rate of photosynthesis. [3 marks]
- Photosynthesis is enzyme-controlled; temperature influences enzyme activity (1)
- As temperature increases, enzyme activity and kinetic energy increase → higher rate (1)
- Beyond optimum temperature, enzymes denature → rate decreases (1)
Section B: Diagram and Data Interpretation
8.
(a) Label the parts A, B, and C. [3 marks]
A: Thylakoid membrane (1)
B: Granum (accept: stack of thylakoids) (1)
C: Stroma (1)
(b) State the location of the light-dependent reactions. [1 mark]
Thylakoid membrane (1)
(c) Explain the role of part C in the light-independent reactions. [2 marks]
- The stroma contains the enzymes for the Calvin cycle (1)
- It is the site where CO₂ is fixed and sugars are synthesised (1)
9.
(a) With reference to Figure 2, state the wavelengths of light absorbed most strongly by chlorophyll a. [2 marks]
- Blue light (around 430 nm) (1)
- Red light (around 662 nm) (1)
(Accept stated wavelength ranges.)
(b) Explain why chlorophyll appears green based on the absorption spectrum. [3 marks]
- Chlorophyll strongly absorbs blue and red light (1)
- Green light (500–550 nm) is absorbed very weakly (reflected or transmitted) (1)
- The green light reflected reaches the observer’s eye, so chlorophyll appears green (1)
10.
(a) Using the data, describe the relationship between light intensity and the rate of photosynthesis. [2 marks]
- As light intensity increases from 0 to 800 lux, the rate increases (1)
- The rate plateaus at higher intensities (800–1200 lux) (1)
(b) Explain the shape of the curve with reference to limiting factors. [3 marks]
- Initially, light is the limiting factor (1)
- Increasing light increases rate until another factor becomes limiting (1)
- At the plateau, factors like CO₂ concentration or temperature become limiting (1)
11.
(a) With reference to Figure 3, describe the flow of electrons from photosystem II to photosystem I. [4 marks]
- Light energy excites electrons in photosystem II (1)
- Excited electrons are passed to an electron transport chain (1)
- Electrons travel through cytochrome complex and are transferred to plastocyanin (1)
- Plastocyanin carries electrons to photosystem I (1)
(b) Explain how the electron flow leads to ATP synthesis. [4 marks]
- Energy from electrons is used to pump protons (H⁺) into the thylakoid space (1)
- This establishes a proton gradient across the thylakoid membrane (1)
- Protons flow back through ATP synthase (1)
- The flow drives the synthesis of ATP (chemiosmosis) (1)
12.
(a) Compare the response of Species X and Species Y to increasing CO₂ concentration. [2 marks]
- Both species show an increased rate with higher CO₂ (1)
- Species X plateaus at 400 ppm, while Species Y continues to show a steady increase (1)
(b) Suggest a reason for the difference in the response of Species Y at high CO₂ concentration. [2 marks]
- Species Y may be a C3 plant with a lower affinity for CO₂ than Species X (1)
- Species X could be a C4 plant that is CO₂‑saturated at a lower concentration (1)
(Also accept: differences in RuBisCO kinetics; stomatal differences; CO₂‑compensation point.)
Section C: Extended Response
13. Describe how light energy is converted into chemical energy in the form of ATP during the light-dependent reactions of photosynthesis. [8 marks]
Marking points (any 8 of the following):
- Light energy is absorbed by chlorophyll molecules in the thylakoid membrane
- Electrons in chlorophyll become excited (raised to a higher energy level)
- Excited electrons are passed to an electron transport chain
- Energy from electrons is used to pump protons (H⁺) into the thylakoid interior
- This creates a proton gradient (difference in proton concentration across the membrane)
- Protons flow back into the stroma through ATP synthase
- This flow (chemiosmosis) drives the synthesis of ATP from ADP and inorganic phosphate
- Photolysis of water provides replacement electrons for chlorophyll
- The process occurs in photosystem II and photosystem I (non‑cyclic photophosphorylation)
(8 marks maximum.)
14. Explain the role of NADP in photosynthesis and describe how it is reduced. [4 marks]
Marking points (any 4):
- NADP is a coenzyme that acts as a hydrogen/electron carrier
- It accepts electrons and H⁺ ions to form reduced NADP (NADPH)
- Reduction occurs in the stroma, catalysed by NADP reductase
- The electrons come from photosystem I
- NADPH carries reducing power to the Calvin cycle for carbon fixation
15. Compare cyclic and non-cyclic photophosphorylation. [6 marks]
Similarities (2 marks):
- Both occur in the thylakoid membrane (1)
- Both produce ATP via chemiosmosis (1)
Differences (4 marks):
- Cyclic involves only photosystem I; non-cyclic involves both photosystems I and II (1)
- Cyclic produces ATP only; non-cyclic produces ATP, NADPH, and O₂ (1)
- In cyclic, electrons return to photosystem I; in non-cyclic, electrons are replaced by photolysis of water (1)
- Cyclic does not involve photolysis or NADP reduction; non-cyclic does (1)
(Total 6 marks.)
16. Discuss how plants adapted to arid conditions carry out photosynthesis efficiently. [6 marks]
Marking points (any 6):
- Stomata open at night (reducing daytime water loss) – CAM photosynthesis
- CO₂ is fixed into organic acids at night and released during the day for the Calvin cycle
- Thick waxy cuticle reduces water loss by transpiration
- Reduced leaf surface area (spines, needles) minimises water loss
- Deep root systems to obtain water from deep soil layers
- Succulent tissues store water for dry periods
- C4 pathway: spatial separation of initial carbon fixation (mesophyll cells) and Calvin cycle (bundle sheath cells), increasing CO₂ concentration at RuBisCO and reducing photorespiration
17. With reference to the structure of a leaf, explain how it is adapted for photosynthesis. [6 marks]
Marking points (any 6):
- Large, flat surface area for maximum light interception
- Thin structure for short diffusion distance for gases
- Palisade mesophyll cells are tightly packed and contain many chloroplasts for light absorption
- Spongy mesophyll contains air spaces for rapid gas exchange
- Stomata allow CO₂ entry and O₂ exit; guard cells regulate opening
- Vascular bundles (xylem and phloem) supply water and remove sugars
18.
(a) Calculate the percentage increase in the rate of photosynthesis from low light to high light at 25°C. [2 marks]
Rate at low light = 5 bubbles/min; rate at high light = 25 bubbles/min
Increase = 25 – 5 = 20 bubbles/min (1)
Percentage increase = (20 ÷ 5) × 100 = 400% (1)
(b) Explain the effect of increasing temperature from 25°C to 35°C on the rate of photosynthesis. [3 marks]
- Rate increased from 25 to 30 bubbles/min (1)
- Higher temperature increases the kinetic energy of enzyme and substrate molecules, increasing enzyme activity (1)
- At 35°C, temperature is closer to or at the optimum for the Calvin‑cycle enzymes (1)
(c) Suggest why adding extra CO₂ increased the rate of photosynthesis. [2 marks]
- CO₂ is a substrate for the Calvin cycle (1)
- At high light and temperature, CO₂ may have been the limiting factor; extra CO₂ allows faster carbon fixation (1)
19. Discuss the significance of photosynthesis in maintaining the balance of atmospheric oxygen and carbon dioxide. [5 marks]
Marking points (any 5):
- Photosynthesis removes CO₂ from the atmosphere and releases O₂
- It counterbalances respiration and combustion processes that consume O₂ and release CO₂
- Photosynthesis is the primary source of atmospheric O₂
- It plays a key role in the carbon cycle
- By absorbing CO₂ it mitigates the greenhouse effect
- It supports the survival of aerobic organisms
20.
(a) With reference to the absorption spectrum of chlorophyll, explain the results for blue and green light. [4 marks]
- Chlorophyll absorbs blue light very strongly (1) → high rate of photosynthesis under blue light (1)
- Chlorophyll absorbs green light poorly (it is reflected/transmitted) (1) → low rate of photosynthesis under green light (1)
(b) Predict the rate of photosynthesis under white light and explain your reasoning. [2 marks]
- Rate would be higher than under any single coloured light (1)
- White light contains all wavelengths, allowing chlorophyll to absorb both blue and red light simultaneously (1)
(Accept a reasonable estimate, e.g., 5.0 cm³ O₂ m⁻² s⁻¹.)
End of Answer Key