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A Level H1 Biology Plant Biology Quiz

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A-Level Biology H1 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.
You are advised to spend approximately 1 minute per mark.

Section A: Structure and Function (Questions 1–5)

1. Fig. 1.1 shows a transverse section of a leaf from a mesophytic plant.

(Imagine Fig 1.1 showing upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis with stomata, and vascular bundles)

(a) Identify the tissue labelled A (the layer of tightly packed, columnar cells). [1]

(b) State two structural features of the cells in tissue A that adapt them for efficient photosynthesis. [2]

2. Fig. 2.1 shows the structure of a chloroplast.

(a) Name the structure labelled X (the stacked discs). [1]

(b) State the specific photosynthetic pigment located in the membranes of structure X. [1]

3. Describe the role of the cuticle in a leaf and explain how its thickness varies between plants in humid versus arid environments. [3]

4. Fig. 4.1 shows a cross-section of a root hair cell.

(a) Explain how the shape of the root hair cell increases the efficiency of water uptake. [2]

(b) State the process by which mineral ions, such as nitrate, are taken up by root hair cells against a concentration gradient. [1]

5. Distinguish between xylem and phloem in terms of:
(a) The direction of transport. [2]
Xylem: __________________________________________________________________
Phloem: __________________________________________________________________

(b) The type of material transported. [2]
Xylem: __________________________________________________________________
Phloem: __________________________________________________________________

Section B: Photosynthesis and Energy (Questions 6–12)

6. During the light-dependent stage of photosynthesis, photolysis of water occurs.
(a) Write the balanced chemical equation for the photolysis of water. [2]

(b) State two roles of the products of photolysis in photosynthesis. [2]

7. Explain the term photoactivation as it applies to chlorophyll in Photosystem II. [2]

8. Describe the sequence of events in the Calvin Cycle (light-independent reaction) that leads to the production of one molecule of glucose. Include the roles of ATP and reduced NADP (NADPH). [6]

9. Fig. 9.1 shows the effect of light intensity on the rate of photosynthesis at two different temperatures (15°C and 25°C).

(Imagine a graph where rate increases with light intensity then plateaus. The 25°C line plateaus higher than the 15°C line.)

(a) Identify the limiting factor at point A (low light intensity, both curves overlapping). [1]

(b) Explain why the rate of photosynthesis at point B (high light intensity) is higher at 25°C than at 15°C. [3]

10. Explain how cyclic photophosphorylation differs from non-cyclic photophosphorylation in terms of:
(a) The photosystems involved. [2]

(b) The products formed. [2]

11. A herbicide blocks the electron transport chain between Photosystem II and Photosystem I.
Explain the immediate effect of this herbicide on the production of ATP and reduced NADP. [4]

12. State the location of the enzymes responsible for the Krebs cycle in a plant cell and explain why plant cells still require mitochondria despite having chloroplasts. [3]

Section C: Transport and Growth (Questions 13–20)

13. Describe the Mass Flow Hypothesis for the translocation of sucrose in phloem. Include the roles of source, sink, and active transport. [5]

14. Fig. 14.1 shows a potometer used to measure the rate of water uptake by a shoot.

(a) State two assumptions made when using a potometer to estimate the rate of transpiration. [2]

(b) Explain how an increase in wind speed affects the rate of water uptake measured by the potometer. [3]

15. Explain the role of abscisic acid (ABA) in the closure of stomata during water stress. [4]

16. Compare the mechanisms of apical dominance and seed germination with reference to the hormones involved (auxin and gibberellin). [4]

17. Define the term transpiration pull and explain how the properties of water molecules contribute to this process. [3]

18. Explain why C4 plants are more efficient than C3 plants in hot, dry conditions. Refer to the role of PEP carboxylase and spatial separation of reactions. [4]

19. A student investigates the effect of sucrose concentration on the mass of potato cylinders.
(a) Define water potential. [1]

(b) If a potato cylinder gains mass in a 0.2 mol dm⁻³ sucrose solution, what can be deduced about the water potential of the potato cells relative to the solution? [1]

20. Describe the process of double fertilization in angiosperms and state the ploidy level (n, 2n, 3n, etc.) of the resulting structures. [4]

End of Quiz

Answers

A-Level Biology H1 Quiz - Plant Biology (Answer Key)

Total Marks: 40

Section A: Structure and Function

1.
(a) Palisade mesophyll [1]
(b) Any two of:

Contains many chloroplasts [1]
Arranged vertically/columnar to maximize light absorption/minimize shading [1]
Located near the upper surface to receive maximum light [1]
(Max 2)
(c) - Loosely packed cells create large air spaces [1]
Allows for rapid diffusion of CO₂ and O₂ to/from mesophyll cells [1]

2.
(a) Granum (or Thylakoids) [1]
(b) Chlorophyll [1]
(c) - The stroma is the site of the light-independent reactions (Calvin Cycle) [1]

These reactions are enzyme-controlled (e.g., Rubisco), requiring a high concentration of enzymes for efficiency [1]

Role: Waterproof layer to prevent excessive water loss (transpiration) [1]
Humid environment: Thinner cuticle [1] because water conservation is less critical/transpiration rate is lower due to high humidity. [1]
Arid environment: Thicker cuticle [1] to minimize water loss. (Note: Question asks for variation explanation, award marks for comparative logic).
(Max 3: 1 for role, 2 for comparison logic)

4.
(a) - Increases surface area [1]

Increases the rate of osmosis/water uptake [1]
(b) Active transport [1]

5.
(a) Xylem: Unidirectional (upwards only / root to leaf) [1]
Phloem: Bidirectional (source to sink / can be up or down) [1]
(b) Xylem: Water and mineral ions [1]
Phloem: Organic solutes / Sucrose / Amino acids [1]

Section B: Photosynthesis and Energy

6.
(a) $2H_2O \rightarrow 4H^+ + 4e^- + O_2$ [2] (1 for correct reactants/products, 1 for balancing)
(b) Any two:

Electrons replace those lost by chlorophyll (in PSII) [1]
Protons ( $H^+$ ) contribute to the proton gradient for chemiosmosis/ATP synthesis [1]
Oxygen is released as a by-product [1]
(Max 2)

Chlorophyll absorbs light energy [1]
Electrons are excited/raised to a higher energy level [1]

CO₂ combines with Ribulose Bisphosphate (RuBP) [1]
Catalyzed by Rubisco [1]
Forms two molecules of Glycerate-3-phosphate (GP) [1]
GP is reduced to Triose Phosphate (TP) [1]
Using ATP (for energy) and Reduced NADP (for hydrogen/electrons) [1]
Some TP is converted to glucose/organic molecules, most is regenerated to RuBP [1]
(Max 6)

9.
(a) Light intensity [1]
(b) - At high light, light is no longer the limiting factor [1]

Temperature affects the rate of enzyme-controlled reactions (Calvin cycle) [1]
25°C is closer to the optimum temperature for these enzymes than 15°C, so kinetic energy/collision rate is higher [1]

10.
(a) Cyclic: Involves only Photosystem I [1]
Non-cyclic: Involves Photosystem II and Photosystem I [1]
(b) Cyclic: Produces ATP only [1]
Non-cyclic: Produces ATP, Reduced NADP, and Oxygen [1]

11.

Electron flow from PSII to PSI is stopped [1]
Non-cyclic photophosphorylation cannot occur [1]
No proton gradient generated across thylakoid membrane (from ETC) [1]
Therefore, no ATP is produced via chemiosmosis, and no Reduced NADP is formed (as electrons don't reach NADP) [1]

12.

Mitochondrial matrix [1]
Plant cells need mitochondria to produce ATP via aerobic respiration [1]
Chloroplasts only produce ATP during the day/light; mitochondria provide ATP for cellular processes at night and in non-photosynthetic tissues [1]

Section C: Transport and Growth

13.

Sucrose is actively loaded into phloem sieve tubes at the source (leaf) [1]
This lowers water potential in the phloem [1]
Water enters phloem from xylem by osmosis [1]
Creates high hydrostatic pressure at the source [1]
Mass flow of sucrose solution occurs towards the sink (low pressure) where sucrose is unloaded [1]

14.
(a) Any two:

Rate of water uptake equals rate of transpiration [1]
No water is used for photosynthesis/turgor/growth [1]
The apparatus is watertight [1]
(Max 2)
(b) - Wind removes water vapor from around the leaf [1]
Maintains a steep water potential/concentration gradient between leaf and air [1]
Increases the rate of diffusion/transpiration, thus increasing water uptake [1]

15.

Water stress causes ABA production [1]
ABA binds to receptors on guard cell membrane [1]
Causes $K^+$ channels to open, $K^+$ leaves guard cells [1]
Water potential increases (becomes less negative), water leaves by osmosis, guard cells become flaccid, stomata close [1]

16.

Apical dominance: Auxin produced in apical bud inhibits lateral bud growth [1]
Seed germination: Gibberellin stimulates the production of amylase [1]
Amylase breaks down starch to maltose/glucose for respiration/growth [1]
Auxin maintains dominance; Gibberellin breaks dormancy [1]

17.

Transpiration pull is the upward pull of water in the xylem due to transpiration [1]
Water molecules are cohesive (hydrogen bonds between water molecules) [1]
This allows water to be pulled up as a continuous column without breaking [1]

18.

C4 plants use PEP carboxylase which has a higher affinity for CO₂ than Rubisco [1]
PEP carboxylase fixes CO₂ into a 4-carbon compound in mesophyll cells [1]
This is transported to bundle sheath cells where CO₂ is released at high concentration [1]
High CO₂ concentration minimizes photorespiration (competition with O₂ at Rubisco active site) [1]

19.
(a) The tendency of water molecules to move from one region to another (or chemical potential of water) [1]
(b) The water potential of the potato cells is lower (more negative) than the solution [1]

20.

One male gamete fuses with the egg cell to form the zygote (2n) [1]
The other male gamete fuses with the two polar nuclei [1]
To form the triploid endosperm nucleus (3n) [1]
This ensures food supply for the developing embryo [1]
(Note: 1 mark for describing the two fusions, 1 mark for correct ploidy of zygote, 1 mark for correct ploidy of endosperm, 1 mark for clarity/completeness)