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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:
- This quiz contains 20 questions on Plant Biology (Topic 10: Nutrition and Transport in Flowering Plants).
- Answer ALL questions in the spaces provided.
- The number of marks for each question or part is shown in brackets [ ].
- Where appropriate, show your working and use correct biological terminology.
- Diagrams should be drawn with a sharp pencil and clearly labelled.
Section A: Short Answer (10 marks)
Answer all questions in this section. Questions 1-5.
1. Name the process by which plants lose water vapour to the atmosphere through their leaves. [1]
2. State the word equation for photosynthesis. [2]
3. Identify the two types of vascular tissue found in flowering plants and state the main substance transported by each. [2]
(i) Tissue: __________________ transports: __________________
(ii) Tissue: __________________ transports: __________________
4. Name the pores found mainly on the lower epidermis of leaves that allow gas exchange. [1]
5. State one structural adaptation of a root hair cell that makes it efficient for absorbing water and mineral ions. [1]
Section B: Structured Questions (10 marks)
Answer all questions in this section. Questions 6-10.
6. Define the term translocation. [1]
7. Name the green pigment found in chloroplasts that absorbs light energy for photosynthesis. [1]
8. State what is meant by a limiting factor in the context of photosynthesis. [1]
9. The diagram below shows a cross-section of a dicotyledonous leaf as seen under a light microscope.
[Diagram: Cross-section of leaf showing upper epidermis, palisade mesophyll,
spongy mesophyll, lower epidermis, stomata, guard cells, xylem, phloem]
(a) Name the tissue layer labelled P (the closely packed, elongated cells just below the upper epidermis). [1]
(b) Explain how the arrangement of cells in layer P is adapted for its function. [2]
(c) Identify the structures labelled Q (found in the lower epidermis) and state their function. [2]
Structure: __________________
Function: _________________________________________________________
(d) Explain why there are more of the structures labelled Q on the lower epidermis than on the upper epidermis of most leaves. [2]
10. A student investigated the effect of light intensity on the rate of photosynthesis in an aquatic plant. The apparatus was set up as shown below, and the number of oxygen bubbles produced per minute was counted at different distances from a lamp.
[Diagram: Beaker of water with aquatic plant, inverted funnel, test tube
collecting gas bubbles, lamp at variable distance]
The results are shown in the table:
| Distance from lamp (cm) | Number of bubbles per minute |
|---|---|
| 10 | 45 |
| 20 | 38 |
| 30 | 28 |
| 40 | 18 |
| 50 | 12 |
| 60 | 8 |
(a) Plot a graph of the results on the grid below. Label both axes clearly. [3]
[Blank graph grid with axes]
(b) Describe the relationship between the distance from the lamp and the rate of photosynthesis. [2]
(c) Explain the relationship you described in (b) in terms of light intensity and the process of photosynthesis. [2]
(d) Suggest one factor, other than light intensity, that could limit the rate of photosynthesis in this investigation when the lamp is very close to the plant. Explain your answer. [2]
Section C: Data Response Questions (10 marks)
Answer all questions in this section. Questions 11-15.
11. A potometer was used to investigate the effect of environmental conditions on the rate of transpiration in a leafy shoot. The apparatus was set up as shown, and the distance moved by the air bubble in the capillary tube was recorded every 5 minutes under different conditions.
[Diagram: Potometer with leafy shoot, capillary tube, air bubble, reservoir]
The table shows the distance moved by the air bubble under four different conditions:
| Condition | Distance moved by bubble in 15 minutes (mm) |
|---|---|
| A: Still air, room temperature (25°C) | 24 |
| B: Moving air (fan), room temperature (25°C) | 48 |
| C: Still air, warm temperature (35°C) | 42 |
| D: Still air, high humidity | 12 |
(a) Calculate the rate of transpiration (in mm per minute) for condition B. Show your working. [2]
(b) Compare the results for conditions A and B. Explain why the rate of transpiration differs between these two conditions. [3]
(c) Explain why the rate of transpiration is lowest in condition D. [2]
12. Describe the pathway taken by a water molecule from the soil outside a root to the atmosphere outside a leaf. Name the tissues and processes involved. [3]
13. State two environmental factors that increase the rate of transpiration and explain how each factor has its effect. [2]
Factor 1: __________________
Explanation: _________________________________________________________
Factor 2: __________________
Explanation: _________________________________________________________
14. Explain why a plant wilts if it loses water faster than it can absorb water from the soil. [2]
15. A student placed a potted plant inside a sealed plastic bag for 24 hours. Droplets of water were observed on the inside of the bag. Name the process responsible and explain why the droplets formed. [1]
Section D: Extended Questions (10 marks)
Answer all questions in this section. Questions 16-20.
16. Compare the structure and function of xylem and phloem. [2]
17. Explain how the root system of a flowering plant is adapted for the absorption of water and mineral ions. [2]
18. A farmer grows tomato plants in a greenhouse. During winter, she adds extra carbon dioxide to the air and uses heaters to maintain a temperature of 25°C. Explain why these measures increase the yield of tomatoes. [2]
19. Describe how you would test a leaf to show that it contains starch. Explain the purpose of each step. [2]
20. Discuss the importance of transpiration in flowering plants. Include both advantages and potential disadvantages in your answer. [2]
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 through their leaves. [1]
Answer: Transpiration [1]
Marking note: Accept "transpiration." Do not accept "evaporation" alone (evaporation is part of transpiration but not the complete process). Do not accept "guttation."
2. State the word equation for photosynthesis. [2]
Answer: Carbon dioxide + Water → Glucose + Oxygen [2]
Marking note:
- Award [1] for correct reactants (carbon dioxide AND water)
- Award [1] for correct products (glucose AND oxygen)
- Accept "light energy" and "chlorophyll" written above/below the arrow, but these are not required for the marks
- Do not accept chemical formulae unless the question specifically asks for them; word equation is required
3. Identify the two types of vascular tissue found in flowering plants and state the main substance transported by each. [2]
Answer:
- (i) Tissue: Xylem transports: Water (and dissolved mineral ions) [1]
- (ii) Tissue: Phloem transports: Sucrose / food / organic substances / products of photosynthesis [1]
Marking note: Award [1] for each correct tissue-substance pair. Accept "mineral salts" or "mineral ions" for xylem. Accept "sugars," "amino acids," or "assimilates" for phloem. Do not accept "glucose" for phloem (sucrose is the transported form).
4. Name the pores found mainly on the lower epidermis of leaves that allow gas exchange. [1]
Answer: Stomata (singular: stoma) [1]
Marking note: Accept "stomata" or "stoma." Do not accept "guard cells" (these are the cells surrounding the pore, not the pore itself).
5. State one structural adaptation of a root hair cell that makes it efficient for absorbing water and mineral ions. [1]
Answer: Any ONE of:
- Long, narrow extension/projection (root hair) that increases surface area to volume ratio [1]
- Thin cell wall for short diffusion distance [1]
- Many mitochondria to provide ATP/energy for active transport of mineral ions [1]
- Cell membrane contains many carrier proteins for active transport [1]
- No cuticle, allowing water to enter freely [1]
Marking note: Award [1] for any valid structural adaptation with brief functional link. The adaptation must be structural (not just "absorbs water quickly").
Section B: Structured Questions (10 marks)
6. Define the term translocation. [1]
Answer: Translocation is the transport of manufactured food substances (sucrose and amino acids) in the phloem from the leaves (source) to other parts of the plant (sinks) where they are used or stored. [1]
Marking note: Accept definitions that include: (a) transport in phloem, AND (b) transport of food/sucrose/organic substances. Award [1] if both elements are present. Do not accept "transport in xylem" or "transport of water."
7. Name the green pigment found in chloroplasts that absorbs light energy for photosynthesis. [1]
Answer: Chlorophyll [1]
Marking note: Accept "chlorophyll." Do not accept "chloroplast" (the organelle, not the pigment).
8. State what is meant by a limiting factor in the context of photosynthesis. [1]
Answer: A limiting factor is a factor/condition that is in short supply or at a sub-optimal level, which restricts the rate of photosynthesis when all other factors are at favourable levels. [1]
Marking note: Accept definitions that convey: a factor that directly affects/limits the rate of the process when its level is low/insufficient. Accept reference to light intensity, carbon dioxide concentration, or temperature as examples, but the definition must be general.
9. Leaf cross-section diagram questions.
(a) Name the tissue layer labelled P (the closely packed, elongated cells just below the upper epidermis). [1]
Answer: Palisade mesophyll (layer) [1]
Marking note: Accept "palisade mesophyll," "palisade tissue," or "palisade cells." Do not accept "mesophyll" alone.
(b) Explain how the arrangement of cells in layer P is adapted for its function. [2]
Answer:
- The palisade mesophyll cells are closely packed and elongated/columnar in shape, arranged vertically/at right angles to the leaf surface [1]
- This arrangement allows many cells to be packed into a small space, maximising the number of chloroplasts exposed to sunlight for maximum light absorption for photosynthesis [1]
Marking note:
- Award [1] for describing the arrangement (closely packed, elongated, vertical orientation)
- Award [1] for linking to function (maximises light absorption / contains many chloroplasts for photosynthesis)
- Accept reference to chloroplasts moving within cells to optimise light capture
(c) Identify the structures labelled Q (found in the lower epidermis) and state their function. [2]
Answer:
- Structure: Stomata (singular: stoma) [1]
- Function: Allow gas exchange — carbon dioxide enters the leaf for photosynthesis and oxygen exits; also the site where water vapour exits during transpiration [1]
Marking note: Award [1] for correct identification. Award [1] for function that includes gas exchange (CO₂ in, O₂ out) OR water vapour loss. Accept both.
(d) Explain why there are more of the structures labelled Q on the lower epidermis than on the upper epidermis of most leaves. [2]
Answer:
- The lower epidermis is shaded from direct sunlight, so the temperature is lower [1]
- This reduces the rate of evaporation/water loss from the stomata, helping the plant conserve water while still allowing gas exchange for photosynthesis [1]
Marking note:
- Award [1] for identifying that the lower surface is cooler/less exposed to sun
- Award [1] for linking this to reduced water loss/transpiration
- Accept: "reduces water loss by evaporation" or "prevents excessive transpiration"
10. Photosynthesis investigation with aquatic plant.
(a) Plot a graph of the results on the grid below. Label both axes clearly. [3]
Answer: Graph should show:
- X-axis: Distance from lamp (cm) — correctly scaled and labelled [1]
- Y-axis: Number of bubbles per minute — correctly scaled and labelled [1]
- Plotting: All 6 points plotted accurately (± half a small square), with a smooth best-fit curve or straight line drawn [1]
Marking note:
- Award [1] for each criterion
- The graph should show a decreasing curve/line (as distance increases, bubble count decreases)
- Deduct [1] if axes are not labelled or are swapped
- Accept "Rate of photosynthesis (bubbles per minute)" on the y-axis
(b) Describe the relationship between the distance from the lamp and the rate of photosynthesis. [2]
Answer:
- As the distance from the lamp increases, the rate of photosynthesis (number of bubbles per minute) decreases [1]
- The relationship is not linear; the rate decreases more rapidly at shorter distances and the decrease becomes more gradual at greater distances / the rate of decrease slows down [1]
Marking note:
- Award [1] for stating the inverse relationship (distance increases → rate decreases)
- Award [1] for describing the non-linear nature OR for using data to illustrate (e.g., "from 10 cm to 20 cm, the rate drops by 7 bubbles/min, but from 50 cm to 60 cm, it only drops by 4 bubbles/min")
(c) Explain the relationship you described in (b) in terms of light intensity and the process of photosynthesis. [2]
Answer:
- As the distance from the lamp increases, the light intensity decreases (light intensity is inversely proportional to the square of the distance) [1]
- Light is required for the light-dependent reactions of photosynthesis; with lower light intensity, less light energy is absorbed by chlorophyll, so less photolysis of water occurs and fewer ATP and NADPH are produced, reducing the rate of the light-independent reactions and thus the overall rate of photosynthesis [1]
Marking note:
- Award [1] for linking increased distance to decreased light intensity
- Award [1] for explaining how reduced light intensity affects photosynthesis (less light energy absorbed → slower light-dependent reactions → slower overall photosynthesis)
- Accept reference to light as an energy source for photosynthesis
(d) Suggest one factor, other than light intensity, that could limit the rate of photosynthesis in this investigation when the lamp is very close to the plant. Explain your answer. [2]
Answer:
- Factor: Carbon dioxide concentration [1]
- Explanation: When the lamp is very close, light intensity is high and no longer limiting; the rate of photosynthesis may then be limited by the availability of carbon dioxide, which is a reactant/substrate for the light-independent reactions (Calvin cycle) [1]
OR
- Factor: Temperature [1]
- Explanation: Photosynthesis is enzyme-controlled; if the temperature is too low, enzyme activity is reduced, limiting the rate of the light-independent reactions even when light is abundant [1]
Marking note:
- Award [1] for a valid factor (CO₂ concentration or temperature)
- Award [1] for a correct explanation linking the factor to its role in photosynthesis and why it becomes limiting at high light intensity
- Do not accept "water" (aquatic plant is submerged) or "number of leaves" (not a variable in this context)
Section C: Data Response Questions (10 marks)
11. Potometer investigation.
(a) Calculate the rate of transpiration (in mm per minute) for condition B. Show your working. [2]
Answer: Rate = Distance / Time = 48 mm / 15 min = 3.2 mm/min [2]
Marking note:
- Award [1] for correct working (48 ÷ 15)
- Award [1] for correct answer with correct units (3.2 mm/min)
- Accept 3.2 mm per minute
(b) Compare the results for conditions A and B. Explain why the rate of transpiration differs between these two conditions. [3]
Answer:
- Condition B (moving air) has a higher rate of transpiration (48 mm/15 min) than condition A (still air) (24 mm/15 min); the rate is doubled [1]
- Moving air (wind/fan) removes water vapour from the area around the leaf/stomata, maintaining a steep water vapour concentration gradient between the leaf and the surrounding air [1]
- This increases the rate of diffusion of water vapour out of the leaf, thus increasing the rate of transpiration [1]
Marking note:
- Award [1] for stating that B has a higher rate (with data comparison)
- Award [1] for explaining that moving air removes water vapour/maintains concentration gradient
- Award [1] for linking this to increased diffusion/transpiration rate
- Accept reference to "reduces the boundary layer of still air" or "prevents humidity build-up"
(c) Explain why the rate of transpiration is lowest in condition D. [2]
Answer:
- Condition D has high humidity, meaning the air already contains a high concentration of water vapour [1]
- This reduces the water vapour concentration gradient between the leaf (high water vapour concentration inside) and the outside air, so the rate of diffusion of water vapour out of the leaf is reduced, lowering the rate of transpiration [1]
Marking note:
- Award [1] for identifying that high humidity reduces the concentration gradient
- Award [1] for linking reduced gradient to reduced diffusion/transpiration rate
12. Describe the pathway taken by a water molecule from the soil outside a root to the atmosphere outside a leaf. Name the tissues and processes involved. [3]
Answer:
- Water enters the root hair cell by osmosis from the soil [1]
- It moves across the root cortex cells (by osmosis and/or via cell walls/apoplast pathway and cytoplasm/symplast pathway) to the xylem in the vascular bundle [1]
- Water moves up the xylem vessels (by transpiration pull/cohesion-tension) through the stem to the leaves, where it moves into the mesophyll cells and evaporates into air spaces before diffusing out through the stomata as water vapour (transpiration) [1]
Marking note:
- Award [1] for osmosis into root hair cell and movement to xylem
- Award [1] for transport in xylem (transpiration pull)
- Award [1] for evaporation and diffusion out of stomata
- Accept reference to apoplast/symplast pathways, cohesion, adhesion, transpiration stream
13. State two environmental factors that increase the rate of transpiration and explain how each factor has its effect. [2]
Answer: Any TWO of:
- Factor 1: Increased temperature — increases the kinetic energy of water molecules, so they evaporate faster from the mesophyll cells; also increases the water-holding capacity of the air, maintaining a steeper concentration gradient [1]
- Factor 2: Increased wind speed / moving air — removes water vapour from around the stomata, maintaining a steep water vapour concentration gradient for faster diffusion [1]
- Factor 3: Decreased humidity — increases the water vapour concentration gradient between the leaf and the air, increasing the rate of diffusion of water vapour out of the leaf [1]
- Factor 4: Increased light intensity — stimulates stomatal opening (guard cells become turgid), allowing more water vapour to diffuse out [1]
Marking note: Award [1] for each factor with a correct explanation. The factor must be environmental (not internal/plant factors). Accept any two valid factors.
14. Explain why a plant wilts if it loses water faster than it can absorb water from the soil. [2]
Answer:
- When water loss by transpiration exceeds water uptake by the roots, the plant cells lose water and become flaccid/plasmolysed [1]
- This causes a loss of turgor pressure, so the cells/tissues become soft and the plant stems and leaves droop/wilt [1]
Marking note:
- Award [1] for stating that cells lose water and become flaccid
- Award [1] for linking loss of turgor pressure to wilting/drooping
- Accept reference to turgor pressure maintaining rigidity of non-woody plants
15. A student placed a potted plant inside a sealed plastic bag for 24 hours. Droplets of water were observed on the inside of the bag. Name the process responsible and explain why the droplets formed. [1]
Answer:
- Process: Transpiration [0.5]
- Explanation: Water vapour released from the plant (via transpiration) condenses on the cooler surface of the plastic bag, forming liquid water droplets [0.5]
Marking note: Award [0.5] for naming transpiration and [0.5] for explaining condensation of water vapour. Accept "evaporation from the plant" as part of the explanation.
Section D: Extended Questions (10 marks)
16. Compare the structure and function of xylem and phloem. [2]
Answer:
- Xylem: Made of dead, hollow cells (vessels/tracheids) with lignified walls; transports water and dissolved mineral ions from roots to leaves (unidirectional) [1]
- Phloem: Made of living cells (sieve tubes and companion cells) with sieve plates; transports sucrose and amino acids from leaves (source) to other parts of the plant (sinks) (bidirectional) [1]
Marking note:
- Award [1] for xylem (structure: dead, hollow, lignified; function: water/mineral transport, unidirectional)
- Award [1] for phloem (structure: living, sieve tubes, companion cells; function: sucrose/amino acid transport, bidirectional)
- Must include both structure and function for each to earn the mark.
17. Explain how the root system of a flowering plant is adapted for the absorption of water and mineral ions. [2]
Answer:
- Root hairs (extensions of epidermal cells) greatly increase the surface area for absorption of water and mineral ions [1]
- The root system is extensive and branched, penetrating a large volume of soil to access water and minerals; root hair cells have thin cell walls for short diffusion distance and many mitochondria to provide energy for active transport of mineral ions [1]
Marking note:
- Award [1] for root hairs increasing surface area
- Award [1] for any other valid adaptation (extensive branching, thin cell walls, mitochondria for active transport, no cuticle)
- Accept reference to osmosis for water and active transport for mineral ions
18. A farmer grows tomato plants in a greenhouse. During winter, she adds extra carbon dioxide to the air and uses heaters to maintain a temperature of 25°C. Explain why these measures increase the yield of tomatoes. [2]
Answer:
- Adding extra carbon dioxide increases the concentration of a reactant/substrate for photosynthesis, so the rate of the light-independent reactions (Calvin cycle) increases, producing more glucose/sugars for growth and fruit development [1]
- Maintaining a temperature of 25°C provides an optimum temperature for the enzymes involved in photosynthesis, maximising the rate of reactions; in winter, low temperatures would otherwise slow down enzyme activity and limit photosynthesis [1]
Marking note:
- Award [1] for explaining the effect of added CO₂ (increases rate of photosynthesis → more glucose → more growth/yield)
- Award [1] for explaining the effect of temperature (optimum for enzymes → maximises photosynthesis rate)
- Accept reference to CO₂ as a limiting factor in winter and temperature as a limiting factor
19. Describe how you would test a leaf to show that it contains starch. Explain the purpose of each step. [2]
Answer:
- Step 1: Boil the leaf in water to kill the cells and stop metabolic reactions / to soften the leaf [0.5]
- Step 2: Boil the leaf in ethanol (in a water bath) to remove/decolourise chlorophyll [0.5]
- Step 3: Rinse the leaf in warm water to soften it and remove ethanol [0.5]
- Step 4: Add iodine solution; a blue-black colour indicates the presence of starch [0.5]
Marking note:
- Award [0.5] for each step with a correct purpose, up to [2]
- Steps must be in a logical order
- Accept "decolourise" or "remove chlorophyll" for the ethanol step
- Safety note: ethanol must be heated indirectly (water bath) due to flammability
20. Discuss the importance of transpiration in flowering plants. Include both advantages and potential disadvantages in your answer. [2]
Answer:
- Advantages: Transpiration pulls water up the xylem (transpiration pull), delivering water and dissolved mineral ions to the leaves for photosynthesis and other metabolic processes; it also helps to cool the plant through evaporative cooling [1]
- Disadvantages: Excessive transpiration can lead to water loss and wilting, especially in hot, dry, or windy conditions; if water loss exceeds water uptake, the plant may suffer from dehydration and reduced growth or death [1]
Marking note:
- Award [1] for at least one valid advantage (water/mineral transport, cooling)
- Award [1] for at least one valid disadvantage (wilting, water stress, dehydration)
- Accept any other valid advantage (e.g., maintains turgor pressure) or disadvantage (e.g., energy cost of closing stomata)
END OF ANSWER KEY