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Secondary 3 Biology Plant Biology Quiz
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Questions
Secondary 3 Biology Quiz - Plant Biology
Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ________ / 40
Duration: 40 minutes
Total Marks: 40
Instructions:
- Answer ALL questions.
- Write your answers in the spaces provided.
- The number of marks for each question is shown in brackets [ ].
- You may use a calculator where necessary.
- Diagrams are not drawn to scale unless stated.
Section A: Multiple Choice (Questions 1–5)
Each question carries 1 mark. Choose the most accurate answer.
1. Which cell structure is found in plant cells but NOT in animal cells and is responsible for providing mechanical support?
A. Cell membrane
B. Mitochondrion
C. Cell wall
D. Endoplasmic reticulum
Answer: ________ [1]
2. A student observed a cross-section of a leaf under a microscope. Which tissue would contain the highest density of chloroplasts?
A. Upper epidermis
B. Palisade mesophyll
C. Spongy mesophyll
D. Lower epidermis
Answer: ________ [1]
3. Which of the following is a correct word equation for photosynthesis?
A. glucose + oxygen → carbon dioxide + water
B. carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll)
C. oxygen + water → carbon dioxide + glucose
D. carbon dioxide + glucose → oxygen + water
Answer: ________ [1]
4. In an experiment, a leaf from a destarched plant was partially covered with black paper and exposed to sunlight for 6 hours. When tested with iodine solution, which part of the leaf would turn blue-black?
A. The covered part only
B. The uncovered part only
C. Both the covered and uncovered parts
D. Neither part
Answer: ________ [1]
5. Which environmental factor is most likely to be the limiting factor for photosynthesis on a cold, bright winter day?
A. Light intensity
B. Carbon dioxide concentration
C. Temperature
D. Water availability
Answer: ________ [1]
Section B: Short Answer and Structured Response (Questions 6–15)
6. State two structural differences between a palisade mesophyll cell and a red blood cell. [2]
(i) ___________________________________________________________________________
(ii) ___________________________________________________________________________
7. The diagram below represents a transverse section of a leaf.
┌─────────────────────────────┐
│ Upper epidermis │
│ ┌───────────────────────┐ │
│ │ Palisade mesophyll │ │
│ └───────────────────────┘ │
│ ┌───────────────────────┐ │
│ │ Spongy mesophyll │ │
│ └───────────────────────┘ │
│ Lower epidermis [stoma] │
└─────────────────────────────┘
(a) Label the following on the diagram above: palisade mesophyll, spongy mesophyll, and stoma. [2]
(b) Explain why the palisade mesophyll cells are located near the upper surface of the leaf. [2]
8. A student set up an experiment to investigate the need for light in photosynthesis. A potted plant was destarched by keeping it in darkness for 48 hours. One leaf was then partially covered with aluminium foil and the plant was placed in bright sunlight for 6 hours.
(a) Why was the plant destarched before the experiment? [1]
(b) What is the purpose of covering only part of the leaf (rather than the whole leaf)? [1]
(c) After the experiment, the leaf was tested with iodine solution. Describe the expected results for the covered and uncovered regions. [2]
Covered region: _______________________________________________________________
Uncovered region: _____________________________________________________________
9. Explain how the following adaptations of xylem vessels enable them to transport water efficiently. [3]
(i) Xylem vessels are hollow and have no cell contents.
(ii) Xylem vessels have thick walls reinforced with lignin.
(iii) Xylem vessels are joined end to end to form continuous tubes.
10. The rate of water uptake by a plant shoot was measured over 24 hours using a potometer. The results are shown below.
| Time of day | Rate of water uptake (cm³/hour) |
|---|---|
| 06:00 | 0.5 |
| 09:00 | 2.0 |
| 12:00 | 4.5 |
| 15:00 | 3.8 |
| 18:00 | 1.5 |
| 21:00 | 0.3 |
(a) Describe the trend shown in the data. [2]
(b) Explain why the rate of water uptake is highest at 12:00. [2]
11. Distinguish between transpiration and translocation. [2]
Transpiration: _______________________________________________________________
Translocation: ______________________________________________________________
12. A student placed a healthy potted plant in a sealed transparent bell jar and left it in sunlight for several hours. After some time, droplets of water were observed on the inner surface of the bell jar.
(a) Name the process responsible for the production of water vapour by the plant. [1]
(b) Explain how this process leads to the formation of water droplets on the inner surface of the bell jar. [2]
13. State two factors that would increase the rate of transpiration from a leaf. For each factor, explain how it increases the rate. [4]
Factor 1: ___________________________________________________________________
Explanation: ________________________________________________________________
Factor 2: ___________________________________________________________________
Explanation: ________________________________________________________________
14. The diagram shows a section through a root.
┌──────────────────────────────┐
│ Epidermis [root hair cell] │
│ ┌────────────────────────┐ │
│ │ Cortex │ │
│ └────────────────────────┘ │
│ ┌────────────────────────┐ │
│ │ Xylem Phloem │ │
│ └────────────────────────┘ │
└──────────────────────────────┘
(a) Identify tissue X (central vascular bundle containing xylem and phloem). [1]
(b) Explain how the structure of a root hair cell is adapted for the absorption of water and mineral ions. [3]
15. A variegated leaf (with green and white regions) was destarched, exposed to light for 6 hours, and then tested with iodine solution.
(a) Predict the result for the green region and the white region. [2]
Green region: ________________________________________________________________
White region: _______________________________________________________________
(b) Explain your answer to part (a). [2]
Section C: Extended Response (Questions 16–20)
16. A farmer noticed that his crops were wilting despite regular watering. A soil test revealed that the soil had a very high salt concentration.
Explain, using your knowledge of water potential and osmosis, why the high salt concentration in the soil caused the plant cells to lose water. In your answer, describe what happens to the plant cells at the cellular level. [4]
17. An experiment was set up to investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant (Elodea). The number of oxygen bubbles produced per minute was counted at different distances from a light source. The results are shown below.
| Distance from light (cm) | Light intensity (arbitrary units) | Bubbles per minute |
|---|---|---|
| 10 | 100 | 28 |
| 20 | 25 | 18 |
| 30 | 11 | 10 |
| 40 | 6 | 5 |
| 50 | 4 | 3 |
(a) Describe the relationship between light intensity and the rate of photosynthesis. [2]
(b) Explain the relationship you described in part (a) in terms of the light-dependent stage of photosynthesis. [3]
(c) Suggest what would happen to the rate of photosynthesis if the distance was reduced to 5 cm. Justify your answer. [2]
18. The diagram below shows a section through a stem.
┌──────────────────────────────┐
│ Epidermis │
┌────┴──────────────────────────────┴────┐
│ Cortex │
│ ┌──────────────────────────────┐ │
│ │ Phloem │ │
│ │ ┌──────────────────────┐ │ │
│ │ │ Xylem │ │ │
│ │ └──────────────────────┘ │ │
│ └──────────────────────────────┘ │
└───────────────────────────────────────┘
(a) State one function of the xylem and one function of the phloem. [2]
Xylem: _____________________________________________________________________
Phloem: ____________________________________________________________________
(b) Explain how the structure of phloem sieve tubes is adapted for the transport of sucrose and amino acids. [3]
(c) A ring of bark (including phloem) was removed from around the stem of a tree. After several weeks, the tissue above the ring became swollen. Explain this observation. [3]
19. A student wanted to investigate whether carbon dioxide is necessary for photosynthesis. She set up two bell jars as shown:
- Bell Jar A: Contains a potted plant and a beaker of sodium hydroxide solution (absorbs CO₂).
- Bell Jar B: Contains a potted plant and a beaker of water (does not absorb CO₂).
Both plants were destarched beforehand. After 6 hours of exposure to light, a leaf from each plant was tested with iodine solution.
(a) Identify the independent variable and the dependent variable in this experiment. [2]
Independent variable: ________________________________________________________
Dependent variable: __________________________________________________________
(b) State two controlled variables in this experiment. [2]
(i) ________________________________________________________________________
(ii) ________________________________________________________________________
(c) Predict and explain the results for the leaf from Bell Jar A and Bell Jar B. [3]
Bell Jar A: _________________________________________________________________
Bell Jar B: _________________________________________________________________
20. Explain how the leaf is adapted for efficient gas exchange and photosynthesis. In your answer, refer to at least FOUR structural features of the leaf and explain how each feature supports its function. [5]
Answers
Secondary 3 Biology Quiz - Plant Biology
Answer Key
1. C — Cell wall [1]
Common mistake: Students may select A (cell membrane) because it is present in both plant and animal cells. The cell wall is unique to plant cells and provides mechanical support.
2. B — Palisade mesophyll [1]
The palisade mesophyll contains the highest density of chloroplasts because it is positioned near the upper surface to maximise light absorption.
3. B — carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll) [1]
Common mistake: Students may confuse this with the equation for respiration (option A).
4. B — The uncovered part only [1]
Light cannot pass through the black paper, so photosynthesis cannot occur in the covered region. Without photosynthesis, no starch is produced, and the covered region does not turn blue-black with iodine.
5. C — Temperature [1]
On a cold winter day, enzymes involved in photosynthesis work slowly due to low temperature, making temperature the limiting factor despite high light intensity.
6. [2 marks — 1 mark per correct difference]
(i) Palisade mesophyll cells have a cell wall; red blood cells do not. [1]
(ii) Palisade mesophyll cells contain chloroplasts; red blood cells do not. [1]
Acceptable alternatives: Palisade cells have a large central vacuole (red blood cells do not); palisade cells are rectangular/regular in shape (red blood cells are biconcave discs); palisade cells have chloroplasts (red blood cells have haemoglobin instead). Award 1 mark per valid difference, max 2.
7. (a) [2 marks]
- Palisade mesophyll: upper tissue layer (tightly packed, elongated cells) [1]
- Spongy mesophyll: lower tissue layer (loosely packed cells with air spaces) [1]
- Stoma: small pore in the lower epidermis [1]
Award 1 mark for each correctly labelled structure, max 2.
(b) [2 marks]
The palisade mesophyll is located near the upper surface to receive the most light [1]. This maximises the rate of photosynthesis because the palisade cells contain the highest concentration of chloroplasts [1].
8. (a) [1 mark]
To remove any starch already present in the leaf [1], so that any starch detected at the end of the experiment must have been produced during the experiment.
(b) [1 mark]
To act as a control / to provide a comparison between the covered (no light) and uncovered (light) regions on the same leaf [1].
(c) [2 marks]
Covered region: Remains brown/yellow (no colour change with iodine) / does not turn blue-black [1].
Uncovered region: Turns blue-black [1].
9. [3 marks — 1 mark per correct explanation]
(i) Xylem vessels are hollow and have no cell contents, which reduces resistance to the flow of water / allows water to flow freely through the lumen [1].
(ii) Xylem vessels have thick walls reinforced with lignin, which provides structural support / prevents the vessels from collapsing under the tension created by transpiration pull [1].
(iii) Xylem vessels are joined end to end to form continuous tubes, which allow water to be transported uninterrupted from the roots to the leaves [1].
10. (a) [2 marks]
The rate of water uptake increases from 06:00 to a peak at 12:00 [1], then decreases from 12:00 to 21:00 [1].
(b) [2 marks]
At 12:00, the light intensity is highest [1], which causes the stomata to open fully, increasing the rate of transpiration and therefore the rate of water uptake [1].
11. [2 marks]
Transpiration is the loss of water vapour from the aerial parts of a plant (mainly through stomata) [1].
Translocation is the transport of sucrose and amino acids (food substances) through the phloem from source to sink [1].
12. (a) [1 mark]
Transpiration [1].
(b) [2 marks]
The plant releases water vapour through transpiration via the stomata [1]. The water vapour condenses on the cooler inner surface of the bell jar, forming water droplets [1].
13. [4 marks — 2 marks per factor: 1 for naming, 1 for explanation]
Factor 1: Increased temperature
Explanation: Higher temperature increases the kinetic energy of water molecules, causing faster evaporation from the leaf surface, which increases the water vapour concentration gradient and thus the rate of transpiration.
Factor 2: Increased wind speed / air movement
Explanation: Wind removes the humid air (boundary layer) around the leaf, maintaining a steep water vapour concentration gradient between the inside and outside of the leaf, increasing the rate of transpiration.
Acceptable alternatives: Increased light intensity (causes stomata to open wider, increasing water loss); decreased humidity (increases the concentration gradient); low water availability in soil (triggers stomatal closure — but this decreases transpiration, so only accept if the student correctly identifies it as decreasing the rate). Award 1 mark for factor + 1 mark for correct explanation, max 4.
14. (a) [1 mark]
Vascular bundle / stele [1].
(b) [3 marks]
- Root hair cells have long, thin extensions (root hairs) that greatly increase the surface area for absorption of water and mineral ions [1].
- Root hair cells have a thin cell wall / cell membrane, which shortens the diffusion distance for water and mineral ions [1].
- Root hair cells have a large number of mitochondria / high metabolic activity, which provides energy (ATP) for active transport of mineral ions [1].
Acceptable alternative: Root hair cells have a lower water potential (due to dissolved solutes) compared to the soil solution, creating an osmotic gradient for water uptake.
15. (a) [2 marks]
Green region: Turns blue-black [1].
White region: Remains brown/yellow (no blue-black colour) [1].
(b) [2 marks]
The green region contains chlorophyll [1], which is necessary for photosynthesis to occur and produce starch. The white region lacks chlorophyll, so no photosynthesis occurs and no starch is produced [1].
16. [4 marks]
- The high salt concentration in the soil lowers the water potential of the soil solution [1].
- The water potential of the soil solution becomes lower (more negative) than the water potential of the cell sap in the root hair cells [1].
- Water moves by osmosis from a region of higher water potential (root cell) to a region of lower water potential (soil solution) [1].
- The plant cells lose water and become plasmolysed / the cell membrane pulls away from the cell wall, causing the plant to wilt [1].
Marking note: Students must reference water potential and/or osmosis to gain full marks. Award 1 mark per valid point, max 4.
17. (a) [2 marks]
As light intensity increases, the rate of photosynthesis increases [1]. The relationship is directly proportional / positive correlation [1].
(b) [3 marks]
At higher light intensity, more light energy is absorbed by chlorophyll in the chloroplasts [1]. This increases the rate of the light-dependent reactions, producing more ATP and NADPH [1], which drives the light-independent reactions to produce more glucose, and more oxygen is released as a by-product [1].
(c) [2 marks]
The rate of photosynthesis would increase further [1] because the light intensity would be even higher (closer to the light source), providing more energy for the light-dependent reactions [1].
Accept: Students may note that at very high intensities, the rate may plateau if another factor becomes limiting. Award 1 mark for a reasonable prediction with justification.
18. (a) [2 marks]
Xylem: Transports water and dissolved mineral ions from the roots to the leaves [1].
Phloem: Translocates sucrose and amino acids from source (e.g., leaves) to sink (e.g., roots, fruits, growing regions) [1].
(b) [3 marks]
- Sieve tube elements are living cells joined end to end to form continuous tubes, allowing the flow of sucrose and amino acids [1].
- Sieve plates (perforated end walls) allow the passage of substances between sieve tube elements [1].
- Companion cells are closely associated with sieve tube elements and contain many mitochondria, providing energy (ATP) for active loading of sucrose into the phloem [1].
(c) [3 marks]
Removing the bark (including phloem) disrupts / blocks the translocation of sucrose and amino acids downwards [1]. Sucrose and amino acids accumulate above the ring [1], causing the tissue to swell due to the build-up of organic nutrients / increased osmotic pressure drawing water into the tissue [1].
19. (a) [2 marks]
Independent variable: Presence or absence of carbon dioxide [1].
Dependent variable: Whether starch is produced (result of iodine test) [1].
(b) [2 marks — 1 mark each]
(i) Same light intensity / same distance from light source [1].
(ii) Same temperature / same type and size of plant / same duration of exposure [1].
Acceptable alternatives: Same species of plant, same size of bell jar, same volume of solution, same initial destarching procedure.
(c) [3 marks]
Bell Jar A: The leaf does not turn blue-black / remains brown-yellow [1] because sodium hydroxide absorbed the carbon dioxide, so photosynthesis could not occur and no starch was produced [1].
Bell Jar B: The leaf turns blue-black [1] because carbon dioxide was present, allowing photosynthesis to occur and starch to be produced.
20. [5 marks — award 1 mark per valid structural feature with explanation, max 5]
-
Thin leaf blade / broad, flat shape — Provides a large surface area for absorption of light and carbon dioxide, and shortens the diffusion distance for gases. [1]
-
Palisade mesophyll cells contain many chloroplasts — Maximises the absorption of light energy for photosynthesis. [1]
-
Spongy mesophyll has large air spaces — Allows carbon dioxide to diffuse rapidly to the photosynthetic cells and oxygen to diffuse out. [1]
-
Stomata on the lower epidermis — Allow gas exchange (CO₂ in, O₂ out) between the leaf and the atmosphere. [1]
-
Lower epidermis has more stomata than upper epidermis — Reduces water loss by transpiration (lower epidermis receives less direct sunlight). [1]
-
Waxy cuticle on upper epidermis — Reduces water loss by evaporation from the leaf surface. [1]
-
Xylem in the leaf veins — Supplies water and mineral ions to the photosynthetic cells. [1]
-
Phloem in the leaf veins — Translocates the products of photosynthesis (sucrose) away from the leaf to other parts of the plant. [1]
Award 1 mark per valid feature with correct explanation, max 5. Students must refer to at least 4 features to gain full marks.