Plant Biology
Level 2 — Recall (Definitions, Standard Textbook Problems, Short Derivations) Time Limit: 30 minutes Total Marks: 40
Instructions: Answer all questions. Marks are shown in brackets. Use diagrams where helpful.
Q1. Name the three main plant tissue systems and state the primary function of each. [6]
Q2. Define the following terms: [4] (a) Transpiration (b) Translocation
Q3. Compare xylem and phloem by completing a table with the following headings: main cell type conducting material, direction of transport, and whether transport requires energy (active/passive). [6]
Q4. State the tissue arrangement observed in a typical dicot leaf, from the upper surface to the lower surface. Name four distinct layers/tissues in order. [4]
Q5. Explain the mechanism of stomatal opening in the morning. Refer to guard cells, potassium ions (), water movement, and turgor. [4]
Q6. Match each plant hormone to its primary role: [5]
| Hormone | |
|---|---|
| (a) Auxin | (i) Promotes stomatal closure and dormancy |
| (b) Gibberellin | (ii) Promotes cell elongation and phototropism |
| (c) Cytokinin | (iii) Promotes fruit ripening and abscission |
| (d) Abscisic acid (ABA) | (iv) Promotes stem elongation and seed germination |
| (e) Ethylene | (v) Promotes cell division |
Q7. Define each tropism and state whether the named response is positive or negative: [3] (a) The shoot of a plant bending towards light. (b) The root of a plant growing downwards in response to gravity. (c) A tendril coiling around a support.
Q8. Briefly describe the cohesion–tension theory of water movement up the xylem. Include the terms cohesion, adhesion, and transpiration pull. [4]
Q9. Define alternation of generations and name the two alternating multicellular stages, stating the ploidy (haploid/diploid) of each. [4]
Answer keyMark scheme & solutions
Q1. [6] — 3 tissue systems × (name 1 + function 1)
- Dermal tissue (epidermis): outer protective covering; prevents water loss / gas exchange control. [2]
- Vascular tissue (xylem + phloem): transport of water, minerals, and organic nutrients. [2]
- Ground tissue (parenchyma, collenchyma, sclerenchyma): photosynthesis, storage, and support. [2]
Why: These three systems continuous throughout the plant body define its structural organisation.
Q2. [4] (a) Transpiration — the loss of water vapour from the aerial parts of a plant, mainly through the stomata of leaves. [2] (b) Translocation — the transport of organic solutes (mainly sucrose) through the phloem from source to sink. [2]
Q3. [6] — 1 mark per correct cell/feature (6 cells)
| Feature | Xylem | Phloem |
|---|---|---|
| Conducting material | Water + dissolved minerals | Sugars (sucrose) + organic solutes |
| Direction | Upward (roots → leaves), unidirectional | Bidirectional (source → sink) |
| Energy requirement | Passive (no ATP for flow) | Active (requires ATP for loading) |
Why: Xylem flow is driven by transpiration pull (passive); phloem transport requires active loading of sucrose at the source.
Q4. [4] — 1 mark each, correct order required
- Upper epidermis (with cuticle)
- Palisade mesophyll
- Spongy mesophyll
- Lower epidermis (with stomata / guard cells)
Why: Reflects the light-gradient adaptation — packed palisade near light, air-spaced spongy layer near stomata for gas exchange.
Q5. [4]
- ions are actively pumped into the guard cells. [1]
- This lowers the water potential inside the guard cells. [1]
- Water enters the guard cells by osmosis. [1]
- Guard cells become turgid; their unevenly thickened walls curve apart, opening the stomatal pore. [1]
Why: Solute accumulation drives osmotic water uptake → turgor change opens the pore.
Q6. [5] — 1 mark each (a) Auxin → (ii) (b) Gibberellin → (iv) (c) Cytokinin → (v) (d) ABA → (i) (e) Ethylene → (iii)
Q7. [3] — 1 mark each (a) Phototropism — growth in response to light; bending towards light = positive phototropism. [1] (b) Gravitropism (geotropism) — growth in response to gravity; root growing downwards = positive gravitropism. [1] (c) Thigmotropism — growth in response to touch/contact; tendril coiling = positive thigmotropism. [1]
Q8. [4]
- Water evaporates from mesophyll cells and exits via stomata (transpiration), creating a transpiration pull (tension). [1]
- Water molecules are attracted to each other by hydrogen bonds (cohesion), forming a continuous column. [1]
- Water molecules adhere to the hydrophilic xylem walls (adhesion), helping maintain the column against gravity. [1]
- The tension pulls the unbroken water column up the xylem from roots to leaves. [1]
Q9. [4]
- Alternation of generations — a life cycle in which a plant alternates between a multicellular haploid stage and a multicellular diploid stage. [2]
- Gametophyte — haploid (n), produces gametes. [1]
- Sporophyte — diploid (2n), produces spores by meiosis. [1]
[
{"claim": "Q3: Xylem transport is passive (no ATP for bulk flow), phloem is active (ATP required)", "code": "xylem_energy='passive'; phloem_energy='active'; result = (xylem_energy=='passive' and phloem_energy=='active')"},
{"claim": "Q7: All three named tropic responses are positive", "code": "responses=['positive','positive','positive']; result = all(r=='positive' for r in responses)"},
{"claim": "Q9: Sporophyte is diploid (2n) and gametophyte is haploid (n)", "code": "sporophyte_ploidy=2; gametophyte_ploidy=1; result = (sporophyte_ploidy==2 and gametophyte_ploidy==1)"},
{"claim": "Q5: Stomatal opening driven by K+ influx lowering water potential and osmotic water uptake", "code": "K_direction='in'; water_direction='in'; turgor='increase'; result = (K_direction=='in' and water_direction=='in' and turgor=='increase')"}
]