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O Level Biology Plant Biology Quiz
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Questions
O-Level Biology Quiz - Plant Biology
Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 40
Duration: 45 minutes Total Marks: 40
Instructions:
- Answer ALL questions in the spaces provided.
- The number of marks is given in brackets [ ] at the end of each question or part question.
- Show your working where appropriate.
- Use correct biological terminology throughout.
Section A: Short Answer (10 marks)
Answer all questions in this section.
1. Name the process by which plants lose water vapour to the atmosphere. [1]
2. State the word equation for photosynthesis. [2]
3. Name the two types of vascular tissue found in flowering plants and state the main substance transported by each. [2]
4. State one structural adaptation of a root hair cell and explain how this adaptation helps the cell carry out its function. [2]
5. Define the term translocation as it applies to flowering plants. [1]
Section B: Structured Questions (10 marks)
Answer all questions in this section.
6. Name the pores found in the epidermis of leaves that allow gas exchange, and state one factor that causes them to close. [2]
7. The diagram below shows a cross-section of a typical dicotyledonous leaf.
[Diagram: Cross-section of leaf showing upper epidermis, palisade mesophyll,
spongy mesophyll, lower epidermis, stoma, guard cells, xylem, phloem]
(a) Identify the tissue labelled X (palisade mesophyll) and state its main function. [2]
(b) Explain how the distribution of chloroplasts in the leaf tissues shown relates to the process of photosynthesis. [3]
(c) Describe the role of the guard cells in regulating gas exchange in the leaf. [2]
8. A student investigated the effect of light intensity on the rate of transpiration in a leafy shoot using a potometer. The results are shown in the table below.
| Light Intensity (arbitrary units) | Distance travelled by air bubble (cm) in 10 minutes |
|---|---|
| 0 | 0.5 |
| 2 | 1.8 |
| 4 | 3.2 |
| 6 | 4.5 |
| 8 | 5.1 |
| 10 | 5.3 |
(a) Using the data, describe the relationship between light intensity and the rate of transpiration. [2]
(b) Explain why increasing light intensity affects the rate of transpiration. [3]
(c) Suggest why the rate of transpiration begins to level off at higher light intensities. [1]
Section C: Structured Questions (10 marks)
Answer all questions in this section.
9. A pollen grain lands on the stigma of a flower of the same species.
(a) Describe the route taken by the growing pollen tube from the stigma to the ovule. [3]
(b) Explain the importance of the pollen tube in plant reproduction. [2]
10. The graph below shows the rate of photosynthesis in a plant at different carbon dioxide concentrations, under two different light intensities.
[Graph: Rate of photosynthesis (y-axis) vs. CO₂ concentration (x-axis)
Two curves: High light intensity (upper curve), Low light intensity (lower curve)
Both curves rise then plateau]
(a) Compare the effect of carbon dioxide concentration on the rate of photosynthesis at high light intensity and at low light intensity. [3]
(b) Explain why the rate of photosynthesis levels off at high carbon dioxide concentrations under low light intensity. [2]
Section D: Data-Based and Extended Response (10 marks)
Answer all questions in this section.
11. State one other factor, apart from light intensity and carbon dioxide concentration, that can limit the rate of photosynthesis, and explain how it acts as a limiting factor. [2]
12. Describe the process of water movement from the soil into the root hair cells of a flowering plant, and explain how water is then transported up the stem to the leaves. [5]
13. Explain the importance of nitrate ions and magnesium ions in plant growth. [2]
14. State one difference between aerobic respiration and photosynthesis in plants. [1]
15. Describe how you would test a leaf for the presence of starch. [3]
16. Explain why most plants appear green to the human eye. [2]
17. State the function of the waxy cuticle on the upper epidermis of a leaf. [1]
18. Name the part of the flower that develops into a fruit after fertilisation. [1]
19. Explain why plants need to carry out both photosynthesis and respiration. [2]
20. A farmer grows tomato plants in a greenhouse. Suggest and explain two ways the farmer could increase the rate of photosynthesis of the tomato plants. [4]
END OF QUIZ
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Answers
O-Level Biology Quiz - Plant Biology — Answer Key and Marking Scheme
Total Marks: 40
Section A: Short Answer (10 marks)
1. Name the process by which plants lose water vapour to the atmosphere. [1]
Answer: Transpiration [1]
Marking notes: Accept "transpiration" only. Do not accept "evaporation" alone.
2. State the word equation for photosynthesis. [2]
Answer: Carbon dioxide + Water → Glucose + Oxygen [2] (in the presence of light and chlorophyll)
Marking notes:
- Award [1] for correct reactants (carbon dioxide AND water)
- Award [1] for correct products (glucose AND oxygen)
- Accept "light energy" or "sunlight" written above the arrow
- Chemical symbols are also acceptable for full marks
3. Name the two types of vascular tissue found in flowering plants and state the main substance transported by each. [2]
Answer:
- Xylem — transports water (and dissolved mineral ions) [1]
- Phloem — transports sucrose / food / organic substances [1]
Marking notes:
- Award [1] for each correctly named tissue with its transported substance
- Accept "mineral salts" or "dissolved minerals" for xylem
- Accept "amino acids" or "products of photosynthesis" for phloem
4. State one structural adaptation of a root hair cell and explain how this adaptation helps the cell carry out its function. [2]
Answer:
- Adaptation: Root hair cell has a long, narrow extension / large surface area to volume ratio [1]
- Explanation: This increases the surface area for absorption of water and mineral ions (by osmosis and active transport) [1]
Marking notes:
- Award [1] for correctly stating a structural adaptation
- Award [1] for linking the adaptation to increased absorption
- Accept alternative adaptations, e.g.:
- "Many mitochondria" → "Provide energy (ATP) for active transport of mineral ions"
- "Thin cell wall" → "Reduces diffusion distance for water and ions"
5. Define the term translocation as it applies to flowering plants. [1]
Answer: Translocation is the transport of food substances (sucrose / amino acids) in the phloem from the leaves (source) to other parts of the plant (sink). [1]
Marking notes:
- Award [1] for a definition that includes transport of food/sucrose AND mentions phloem
- Do not accept definitions that refer to water transport
Section B: Structured Questions (10 marks)
6. Name the pores found in the epidermis of leaves that allow gas exchange, and state one factor that causes them to close. [2]
Answer:
- Pores: Stomata (singular: stoma) [1]
- Factor causing closure: (any one of the following) [1]
- Darkness / low light intensity
- High temperature / excessive water loss
- Water stress / drought conditions
- High carbon dioxide concentration inside the leaf
- Abscisic acid (ABA) production
Marking notes:
- Award [1] for "stomata" or "stoma"
- Award [1] for any valid factor that causes stomatal closure
7. Leaf cross-section diagram
(a) Identify the tissue labelled X (palisade mesophyll) and state its main function. [2]
Answer:
- Tissue: Palisade mesophyll (layer) [1]
- Function: Main site of photosynthesis / contains many chloroplasts for absorption of light energy [1]
Marking notes:
- Award [1] for correct identification
- Award [1] for stating photosynthesis or light absorption
(b) Explain how the distribution of chloroplasts in the leaf tissues shown relates to the process of photosynthesis. [3]
Answer:
- Palisade mesophyll cells are located near the upper epidermis and contain the highest density of chloroplasts [1]
- This positions chloroplasts close to the light source for maximum light absorption [1]
- Spongy mesophyll cells contain fewer chloroplasts but have air spaces to allow diffusion of carbon dioxide to photosynthetic cells [1]
Marking notes:
- Award [1] for identifying palisade cells have many chloroplasts
- Award [1] for linking position to light absorption
- Award [1] for mentioning spongy mesophyll and gas exchange/diffusion
(c) Describe the role of the guard cells in regulating gas exchange in the leaf. [2]
Answer:
- Guard cells control the opening and closing of stomata [1]
- When guard cells are turgid (full of water), the stoma opens, allowing carbon dioxide to enter and oxygen to exit; when flaccid, the stoma closes, reducing water loss [1]
Marking notes:
- Award [1] for stating guard cells control stomatal aperture
- Award [1] for explaining the mechanism (turgid = open, flaccid = closed) OR linking to gas exchange/water loss
8. Potometer investigation
(a) Using the data, describe the relationship between light intensity and the rate of transpiration. [2]
Answer:
- As light intensity increases from 0 to 6 arbitrary units, the rate of transpiration increases (distance travelled by air bubble increases from 0.5 cm to 4.5 cm) [1]
- At higher light intensities (8–10 arbitrary units), the rate of transpiration continues to increase but at a decreasing rate / begins to level off (5.1 cm to 5.3 cm) [1]
Marking notes:
- Award [1] for describing the initial increase with data reference
- Award [1] for describing the levelling off at higher intensities
(b) Explain why increasing light intensity affects the rate of transpiration. [3]
Answer:
- Higher light intensity causes stomata to open wider (guard cells become turgid) [1]
- This increases the rate of evaporation of water from the mesophyll cells into the air spaces of the leaf [1]
- Water vapour then diffuses out of the stomata more rapidly, increasing the transpiration rate [1]
Marking notes:
- Award [1] for linking light to stomatal opening
- Award [1] for explaining increased evaporation
- Award [1] for linking to increased diffusion/transpiration rate
(c) Suggest why the rate of transpiration begins to level off at higher light intensities. [1]
Answer:
- The stomata are already fully open / maximum stomatal aperture has been reached [1]
Marking notes:
- Award [1] for any valid reason
- Accept: "Other factors become limiting (e.g., humidity, water availability)"
Section C: Structured Questions (10 marks)
9. Pollen tube growth
(a) Describe the route taken by the growing pollen tube from the stigma to the ovule. [3]
Answer:
- The pollen tube grows from the stigma down through the style [1]
- It grows towards the ovary [1]
- It enters the ovule through the micropyle [1]
Marking notes:
- Award [1] for each correct stage of the route in sequence
- Must include: stigma → style → ovary → ovule (micropyle)
(b) Explain the importance of the pollen tube in plant reproduction. [2]
Answer:
- The pollen tube delivers the male gametes (sperm nuclei) to the ovule [1]
- This allows fertilisation to occur without the need for external water / enables fertilisation in terrestrial environments [1]
Marking notes:
- Award [1] for stating delivery of male gametes
- Award [1] for linking to fertilisation or adaptation to land
10. Photosynthesis graph
(a) Compare the effect of carbon dioxide concentration on the rate of photosynthesis at high light intensity and at low light intensity. [3]
Answer:
- At both light intensities, the rate of photosynthesis increases as carbon dioxide concentration increases, up to a point [1]
- At high light intensity, the maximum rate of photosynthesis achieved is higher than at low light intensity [1]
- At low light intensity, the rate of photosynthesis levels off at a lower carbon dioxide concentration compared to high light intensity [1]
Marking notes:
- Award [1] for each valid comparison
- Must reference both curves
(b) Explain why the rate of photosynthesis levels off at high carbon dioxide concentrations under low light intensity. [2]
Answer:
- At low light intensity, light becomes the limiting factor [1]
- Even with abundant carbon dioxide, the rate of photosynthesis cannot increase further because there is insufficient light energy to drive the light-dependent reactions [1]
Marking notes:
- Award [1] for identifying light as the limiting factor
- Award [1] for explaining why light limits the rate
Section D: Data-Based and Extended Response (10 marks)
11. State one other factor, apart from light intensity and carbon dioxide concentration, that can limit the rate of photosynthesis, and explain how it acts as a limiting factor. [2]
Answer:
- Factor: Temperature [1]
- Explanation: At low temperatures, enzymes involved in photosynthesis (e.g., rubisco) have low kinetic energy, so the rate of reaction is slow; at very high temperatures, enzymes may denature, reducing the rate of photosynthesis [1]
Marking notes:
- Award [1] for a valid factor (temperature, water availability, chlorophyll concentration)
- Award [1] for a correct explanation linked to the factor
12. Describe the process of water movement from the soil into the root hair cells of a flowering plant, and explain how water is then transported up the stem to the leaves. [5]
Answer:
- Water enters root hair cells by osmosis because the water potential in the soil is higher than in the root hair cell (due to dissolved solutes in the cell sap) [1]
- Water moves from the root hair cells across the root cortex to the xylem by osmosis (cell-to-cell or via the apoplast/symplast pathways) [1]
- Once in the xylem, water is transported upwards through the stem [1]
- Transpiration from the leaves creates a tension (suction) that pulls water up the xylem (transpiration pull) [1]
- Cohesion and adhesion of water molecules help maintain a continuous column of water in the xylem [1]
Marking notes:
- Award [1] for each key point
- Accept reference to root pressure as a contributing factor
13. Explain the importance of nitrate ions and magnesium ions in plant growth. [2]
Answer:
- Nitrate ions are needed for the synthesis of amino acids and proteins, which are essential for growth and cell division [1]
- Magnesium ions are a component of chlorophyll, which is necessary for photosynthesis [1]
Marking notes:
- Award [1] for each correct explanation
- Accept "nitrate for DNA/nucleic acids" or "nitrate for chlorophyll" (though magnesium is the primary component)
14. State one difference between aerobic respiration and photosynthesis in plants. [1]
Answer:
- Photosynthesis takes in carbon dioxide and releases oxygen, while aerobic respiration takes in oxygen and releases carbon dioxide [1]
Marking notes:
- Award [1] for any valid difference (e.g., photosynthesis stores energy, respiration releases energy; photosynthesis occurs only in light, respiration occurs all the time; photosynthesis occurs in chloroplasts, respiration in mitochondria)
15. Describe how you would test a leaf for the presence of starch. [3]
Answer:
- Boil the leaf in water to kill it and stop metabolic reactions [1]
- Boil the leaf in ethanol (using a water bath) to remove chlorophyll / decolourise the leaf [1]
- Rinse the leaf in warm water, then add iodine solution; a blue-black colour indicates the presence of starch [1]
Marking notes:
- Award [1] for each step in the correct sequence
- Safety note: ethanol must be heated in a water bath, not over a direct flame
16. Explain why most plants appear green to the human eye. [2]
Answer:
- Chlorophyll, the main photosynthetic pigment in plants, absorbs light in the red and blue regions of the spectrum [1]
- It reflects green light, which is why plants appear green [1]
Marking notes:
- Award [1] for stating chlorophyll absorbs red and blue light
- Award [1] for stating green light is reflected/not absorbed
17. State the function of the waxy cuticle on the upper epidermis of a leaf. [1]
Answer:
- To reduce water loss by evaporation / to prevent desiccation [1]
Marking notes:
- Accept "waterproof layer" or "prevents water loss"
- Accept "protects against pathogens" as an additional function
18. Name the part of the flower that develops into a fruit after fertilisation. [1]
Answer:
- Ovary [1]
Marking notes:
- Do not accept "ovule" (ovule develops into the seed)
19. Explain why plants need to carry out both photosynthesis and respiration. [2]
Answer:
- Photosynthesis produces glucose and oxygen, which are needed for respiration [1]
- Respiration releases energy (ATP) from glucose, which is needed for growth, active transport, and other metabolic processes [1]
Marking notes:
- Award [1] for linking photosynthesis products to respiration
- Award [1] for explaining the role of respiration in energy release
20. A farmer grows tomato plants in a greenhouse. Suggest and explain two ways the farmer could increase the rate of photosynthesis of the tomato plants. [4]
Answer:
- Increase carbon dioxide concentration by using a paraffin heater or releasing CO₂ gas; CO₂ is a raw material for photosynthesis, so increasing its concentration increases the rate of photosynthesis (up to a point) [2]
- Increase light intensity using artificial lighting; light provides the energy for the light-dependent reactions of photosynthesis, so increasing light intensity increases the rate of photosynthesis (up to a point) [2]
Marking notes:
- Award [1] for each valid suggestion and [1] for each correct explanation
- Accept other valid suggestions, e.g., maintaining optimal temperature, providing adequate water
- Must include both suggestion and explanation for each way
END OF ANSWER KEY