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A Level H2 Biology Plant Biology Quiz
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Questions
A-Level Biology H2 Quiz - Plant Biology
Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 40
Duration: 45 minutes
Total Marks: 40
Instructions:
- Answer all questions.
- Write your answers in the spaces provided.
- The number of marks is indicated in brackets [ ] at the end of each question or part question.
- You may use a calculator.
Section A: Photosynthesis Mechanisms (Questions 1-5)
1. Fig. 1.1 shows a simplified diagram of the light-dependent reactions of photosynthesis occurring in the thylakoid membrane of a chloroplast.
(Note: Imagine Fig 1.1 shows Photosystem II (PSII), an electron transport chain, Photosystem I (PSI), and ATP synthase. Arrows indicate electron flow and proton movement.)
(a) With reference to Fig. 1.1, describe the role of water in the process occurring at PSII. [2]
(b) Explain how the movement of electrons from PSII to PSI contributes to the synthesis of ATP. [3]
2. RuBisCO is an enzyme found in the stroma of chloroplasts. It has both carboxylase and oxygenase activity.
(a) Explain why high temperatures often lead to a decrease in the rate of photosynthesis in C3 plants, making reference to the activity of RuBisCO. [3]
(b) C4 plants are better adapted to hot, dry environments than C3 plants. Explain how the anatomy of C4 leaves helps to maintain a high rate of photosynthesis under these conditions. [4]
3. A student investigated the effect of light intensity on the rate of photosynthesis of an aquatic plant. The student measured the volume of oxygen bubbles produced per minute at different distances from a light source.
(a) Suggest why measuring the volume of oxygen bubbles is an indirect measure of the rate of photosynthesis. [2]
(b) The student repeated the experiment at a higher temperature (from 20°C to 30°C). Predict and explain the effect this would have on the rate of photosynthesis at low light intensities. [3]
4. Fig. 4.1 shows a transverse section of a leaf from a xerophytic plant.
(Note: Imagine Fig 4.1 shows thick cuticle, sunken stomata, and rolled leaf structure.)
(a) Identify two features visible in Fig. 4.1 that reduce water loss. [2]
(b) Explain how one of these features reduces the rate of transpiration. [2]
5. Nitrate ions are essential for plant growth.
(a) Describe the role of nitrate ions in the synthesis of biological molecules in plants. [2]
(b) Explain why waterlogged soil often leads to nitrogen deficiency in plants, even if nitrates are present in the soil. [4]
Section B: Data Interpretation and Transport (Questions 6-10)
6. Fig. 6.1 shows the absorption spectrum of chlorophyll a and chlorophyll b, and the action spectrum of photosynthesis.
(Note: Imagine Fig 6.1 plots % Absorption/Rate of Photosynthesis against Wavelength (nm). Chlorophylls peak in blue-violet and red regions. Action spectrum follows similar pattern but with broader peaks.)
(a) Define the term action spectrum. [2]
(b) With reference to Fig. 6.1, explain the relationship between the absorption spectrum of chlorophyll and the action spectrum of photosynthesis. [3]
7. Researchers compared the growth of two types of plants, Type A (C3) and Type B (C4), under different atmospheric CO₂ concentrations. The results are shown in Table 7.1.
Table 7.1: Dry mass of plants (g) after 4 weeks
| CO₂ Concentration (ppm) | Type A (C3) Dry Mass (g) | Type B (C4) Dry Mass (g) |
|---|---|---|
| 200 | 1.2 | 1.1 |
| 400 | 2.5 | 2.4 |
| 800 | 4.8 | 2.6 |
| 1200 | 5.1 | 2.5 |
(a) Describe the effect of increasing CO₂ concentration on the dry mass of Type A plants. [2]
(b) Explain the difference in the response of Type A and Type B plants to CO₂ concentrations above 400 ppm. [4]
8. The transport of sucrose in phloem is explained by the Mass Flow Hypothesis.
(a) Describe how sucrose is loaded into the phloem at the source. [3]
(b) Explain how the loading of sucrose leads to the movement of water into the phloem. [2]
9. Fig. 9.1 shows the structure of a root hair cell.
(a) Explain how the structure of a root hair cell is adapted for the absorption of water. [2]
(b) Water moves from the soil into the root hair cell and then across the cortex to the xylem. Describe the two pathways water can take through the cortex cells. [4]
10. Stomatal opening is controlled by guard cells.
(a) Describe the changes that occur in guard cells that lead to the opening of the stomata. [3]
(b) Explain the role of potassium ions (K⁺) in this process. [2]
Section C: Advanced Concepts in Plant Physiology (Questions 11-15)
11. The Calvin Cycle occurs in the stroma of chloroplasts.
(a) Name the molecule that combines with CO₂ in the first step of the Calvin Cycle. [1]
(b) Explain the role of ATP and Reduced NADP in the Calvin Cycle. [3]
12. Transpiration is the loss of water vapor from plant surfaces.
(a) Define transpiration. [1]
(b) Explain how wind speed affects the rate of transpiration. [2]
13. Plants require magnesium ions for healthy growth.
(a) State the specific role of magnesium ions in plant physiology. [1]
(b) Describe the visible symptoms of magnesium deficiency in plants and explain why they occur. [2]
14. Fig. 14.1 shows the structure of a chloroplast.
(a) Identify the site of the light-independent reactions. [1]
(b) Explain the significance of the large surface area of the thylakoid membranes. [2]
15. Compare C3 and C4 photosynthesis.
(a) State one advantage of C4 photosynthesis over C3 photosynthesis in tropical climates. [1]
(b) Explain why C4 plants require more ATP per molecule of CO₂ fixed than C3 plants. [2]
Section D: Experimental Analysis and Application (Questions 16-20)
16. A scientist uses a potometer to measure the rate of water uptake in a shoot.
(a) State one assumption made when using a potometer to estimate transpiration rate. [1]
(b) Suggest two precautions that must be taken when setting up a potometer to ensure valid results. [2]
17. Limiting factors affect the rate of photosynthesis.
(a) Define the term limiting factor. [1]
(b) Explain why increasing light intensity beyond a certain point does not increase the rate of photosynthesis. [2]
18. Phloem unloading occurs at the sink.
(a) Describe how sucrose is removed from the phloem at the sink. [2]
(b) Explain what happens to the water in the phloem at the sink. [1]
19. Adaptations of hydrophytes (aquatic plants).
(a) Describe one structural adaptation of hydrophyte leaves that facilitates gas exchange. [1]
(b) Explain why hydrophytes often have reduced or absent cuticles. [2]
20. Global climate change impacts plant biology.
(a) Explain how rising global temperatures might affect the distribution of C3 and C4 plants. [2]
(b) Suggest one agricultural strategy to mitigate the effects of drought on crop plants. [1]
Answers
A-Level Biology H2 Quiz - Plant Biology (Answer Key)
Total Marks: 40
Section A: Photosynthesis Mechanisms
1.
(a) Water is split (photolysis) [1] by light energy/photons at PSII, providing electrons to replace those lost by chlorophyll and producing protons (H⁺) and oxygen [1].
(b) Electrons move down the electron transport chain (ETC) from PSII to PSI [1]. Energy released from electron movement is used to pump protons (H⁺) from the stroma into the thylakoid lumen [1]. This creates a proton gradient/proton motive force, which drives ATP synthase to produce ATP via chemiosmosis [1].
2.
(a) High temperatures increase the rate of photorespiration [1]. RuBisCO acts as an oxygenase, binding O₂ instead of CO₂ to RuBP [1]. This produces phosphoglycolate which cannot enter the Calvin cycle directly, reducing the efficiency of carbon fixation/photosynthesis [1].
(b) C4 plants have Kranz anatomy with bundle sheath cells surrounding vascular bundles [1]. Mesophyll cells fix CO₂ into a 4-carbon compound (oxaloacetate/malate) using PEP carboxylase, which has a high affinity for CO₂ and no oxygenase activity [1]. This 4-carbon compound is transported to bundle sheath cells where CO₂ is released [1]. This maintains a high concentration of CO₂ around RuBisCO in bundle sheath cells, suppressing photorespiration even when stomata are partially closed to save water [1].
3.
(a) Oxygen is a product of the light-dependent reactions (photolysis of water) [1]. The rate of oxygen production is proportional to the rate of the light-dependent reactions, which limits the overall rate of photosynthesis [1].
(b) At low light intensities, light is the limiting factor [1]. Increasing temperature increases the kinetic energy of enzymes involved in the light-independent reactions (Calvin cycle) [1]. However, since light is limiting, the rate of ATP/NADPH production does not increase significantly, so the overall rate of photosynthesis will not increase significantly or may only increase slightly due to enzyme kinetics until light becomes non-limiting [1].
4.
(a) Any two from: Thick cuticle [1], Sunken stomata [1], Rolled leaf / hairs on epidermis [1].
(b) If thick cuticle chosen: Reduces evaporation of water from the leaf surface / provides a waterproof barrier [1].
If sunken stomata chosen: Traps moist air in the pit / reduces the water potential gradient between the leaf interior and the atmosphere / reduces air movement over the stomata [1].
If rolled leaf/hairs chosen: Traps moist air / reduces air movement / reduces water potential gradient [1].
5.
(a) Nitrate ions are used to synthesize amino acids [1], which are then used to make proteins / nucleotides / DNA / RNA / chlorophyll [1].
(b) Waterlogged soil has low oxygen concentration / is anaerobic [1]. Root cells cannot perform aerobic respiration [1]. Lack of ATP means active transport of nitrate ions into root hairs cannot occur [1]. Additionally, denitrifying bacteria thrive in anaerobic conditions, converting nitrates into nitrogen gas, reducing nitrate availability [1].
Section B: Data Interpretation and Transport
6.
(a) A graph showing the rate of photosynthesis [1] at different wavelengths of light [1].
(b) The action spectrum closely matches the absorption spectrum of chlorophylls a and b [1]. Peaks in the action spectrum (blue-violet and red regions) correspond to the wavelengths where chlorophyll absorbs light most strongly [1]. This indicates that chlorophylls are the primary pigments driving photosynthesis [1].
7.
(a) As CO₂ concentration increases from 200 to 800 ppm, the dry mass of Type A plants increases significantly [1]. Above 800 ppm, the increase levels off / becomes less significant [1].
(b) Type A (C3) plants are limited by photorespiration at normal CO₂ levels [1]. Increasing CO₂ increases the ratio of CO₂ to O₂ at the active site of RuBisCO, reducing photorespiration and increasing carbon fixation [1]. Type B (C4) plants already concentrate CO₂ around RuBisCO, so they are saturated at lower CO₂ concentrations [1]. Therefore, increasing CO₂ further has little effect on their rate of photosynthesis/growth [1].
8.
(a) Sucrose is actively transported into companion cells/sieve tube elements using H⁺/sucrose co-transporters [1]. This requires ATP to pump H⁺ out of the companion cell, creating a gradient [1]. Sucrose moves down its concentration gradient into the phloem [1].
(b) Loading sucrose lowers the water potential in the phloem [1]. Water moves from the xylem into the phloem by osmosis [1].
9.
(a) Long projection/hair increases surface area [1] for faster absorption of water by osmosis [1].
(b) Apoplast pathway: Water moves through cell walls and intercellular spaces [1]. It does not enter the cytoplasm [1].
Symplast pathway: Water moves through the cytoplasm of cells, connected by plasmodesmata [1]. It moves from cell to cell via osmosis/diffusion [1].
10.
(a) Potassium ions (K⁺) enter guard cells [1]. This lowers the water potential in guard cells [1]. Water enters by osmosis, making guard cells turgid [1]. The uneven thickening of guard cell walls causes them to bend outward, opening the stomatal pore [1].
(b) K⁺ ions are actively pumped into guard cells [1]. This accumulation of solutes lowers the water potential, driving water influx [1].
Section C: Advanced Concepts in Plant Physiology
11.
(a) Ribulose bisphosphate / RuBP [1].
(b) ATP provides energy [1] for the reduction of GP to TP and the regeneration of RuBP [1]. Reduced NADP provides hydrogen/electrons [1] for the reduction of GP to TP.
12.
(a) The loss of water vapor from the aerial parts of the plant, mainly through stomata [1].
(b) Wind removes water vapor from around the leaf surface [1]. This maintains a steep water potential gradient between the leaf interior and the atmosphere, increasing the rate of diffusion/transpiration [1].
13.
(a) Magnesium is a central component of the chlorophyll molecule [1].
(b) Chlorosis / yellowing of leaves [1]. This occurs because magnesium is needed for chlorophyll synthesis, and without it, chlorophyll breaks down or cannot be made, revealing other pigments [1].
14.
(a) Stroma [1].
(b) It provides a large surface area for the attachment of photosystems, electron carriers, and ATP synthase [1], maximizing the rate of light-dependent reactions [1].
15.
(a) C4 plants minimize photorespiration / can keep stomata partially closed to reduce water loss while maintaining photosynthesis [1].
(b) C4 plants use ATP to convert pyruvate back to PEP in mesophyll cells [1]. This additional step requires energy, whereas C3 plants do not have this regeneration cost for the initial CO₂ acceptor [1].
Section D: Experimental Analysis and Application
16.
(a) The rate of water uptake is equal to the rate of transpiration / water loss [1].
(b) Cut the shoot under water to prevent air bubbles entering the xylem [1]; Ensure the apparatus is airtight / use vaseline at joints [1].
17.
(a) A factor that is in shortest supply and thus limits the rate of a physiological process [1].
(b) Another factor (e.g., CO₂ concentration or temperature) becomes limiting [1]. The enzymes or substrates for the light-independent reactions are working at maximum capacity [1].
18.
(a) Sucrose is actively transported out of sieve tubes into sink cells [1]. This may involve co-transport with H⁺ or diffusion if concentration is high [1].
(b) Water potential in the phloem increases, so water leaves the phloem by osmosis and returns to the xylem [1].
19.
(a) Large air spaces / aerenchyma [1] allowing diffusion of gases to submerged parts.
(b) Water loss is not a problem in aquatic environments [1]. A cuticle would impede the direct absorption of water and dissolved minerals/gases through the epidermis [1].
20.
(a) C4 plants may expand their range into hotter/drier areas as they are more efficient under these conditions [1]. C3 plants may struggle in hotter regions due to increased photorespiration unless CO₂ levels rise significantly [1].
(b) Development of drought-resistant crop varieties / irrigation systems / mulching to reduce soil evaporation [1].