Biology • Year 11 • Module 2 • Lesson 7
Plant Structure: Macroscopic and Microscopic
Lock in the key vocabulary, the leaf cross-section layer order, and the structure-function relationships for every major plant organ and tissue.
1. Order the leaf cross-section layers
The seven components of a leaf cross-section are listed below in random order. Number them 1–7 from the upper surface to the lower surface as they would appear in a transverse section under a light microscope. Then, in the right-hand column, state one structural feature of each layer. 14 marks (1 for order, 1 for structural feature each)
| Order (1–7) | Layer | One structural feature |
|---|---|---|
| Spongy mesophyll | ||
| Upper epidermis | ||
| Vascular bundle (xylem + phloem) | ||
| Guard cells and stomata | ||
| Palisade mesophyll | ||
| Waxy cuticle (upper) | ||
| Lower epidermis |
2. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: xylem, phloem, transpiration stream, cohesion-tension, translocation, source, sink, Casparian strip, stomata, guard cells. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | Dead, hollow, lignified tubes that transport water and dissolved minerals upward from roots to leaves. | |
| 2.2 | Living vascular tissue composed of sieve tubes and companion cells that transports dissolved sugars throughout the plant. | |
| 2.3 | The continuous flow of water from roots through xylem to leaves, driven by evaporation from leaf surfaces. | |
| 2.4 | The mechanism driving water up xylem, where hydrogen bonds between water molecules pull the water column upward as transpiration creates tension at the leaf. | |
| 2.5 | The active transport of dissolved sugars through phloem from source to sink regions of the plant. | |
| 2.6 | A region of the plant that produces or releases sugars into the phloem, such as a photosynthesising leaf. | |
| 2.7 | A region of the plant that consumes or stores sugars received from the phloem, such as a growing root or fruit. | |
| 2.8 | A band of waterproof suberin around the walls of endodermal cells that forces water and minerals to pass through the cell membrane before entering vascular tissue. | |
| 2.9 | Pores in the leaf epidermis that open to allow gas exchange and close to reduce water loss. | |
| 2.10 | Pairs of kidney-shaped cells flanking a stomatal pore that control aperture by changing turgor using ATP from their chloroplasts. |
3. Organ function recall
Complete the table. For each plant organ, name one key tissue or structure it contains, and state two functions it performs. Use precise lesson terms. 12 marks (1 per cell)
| Organ | One key tissue or structure inside it | Function 1 | Function 2 |
|---|---|---|---|
| Root | |||
| Stem | |||
| Leaf | |||
| Flower |
4. True or false, with correction
For each statement, circle T or F. If the statement is false, write the corrected version. 10 marks (1 for T/F, 1 for correction where needed)
4.1 Palisade mesophyll cells are located directly above the spongy mesophyll and contain dense chloroplasts. T / F
4.2 The upper epidermis of a leaf contains chloroplasts so it can contribute to photosynthesis. T / F
4.3 Xylem transports water and dissolved minerals upward from roots, while phloem transports dissolved sugars throughout the plant. T / F
4.4 Stomata are found in greater numbers on the upper surface of most leaves, to maximise exposure to sunlight for gas exchange. T / F
4.5 The Casparian strip is a band of waterproof suberin that forces water and minerals through the cell membrane before entering vascular tissue. T / F
5. Build a concept map, leaf anatomy and function
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. "allows", "supplies", "controls"). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: palisade mesophyll · stomata · xylem · guard cells · spongy mesophyll · phloem.
Q1, Leaf cross-section layer order
Correct order (top to bottom): 1. Waxy cuticle (upper). 2. Upper epidermis. 3. Palisade mesophyll. 4. Vascular bundle (xylem + phloem). 5. Spongy mesophyll. 6. Lower epidermis. 7. Guard cells and stomata. (Note: the vascular bundle and spongy mesophyll both occupy the middle zone, either order 4/5 is accepted if clearly justified.)
Sample structural features: Waxy cuticle, non-cellular, secreted by epidermal cells, hydrophobic. Upper epidermis, single layer of flat tightly-packed cells, no chloroplasts. Palisade mesophyll, tall columnar cells, 40–50 chloroplasts each. Vascular bundle, xylem on upper side, phloem on lower, surrounded by bundle sheath cells. Spongy mesophyll, loosely arranged irregular cells with large interconnected air spaces. Lower epidermis, single cell layer, more stomata than upper. Guard cells, kidney-shaped, contain chloroplasts, have unequally thick walls.
Q2, Term–definition matches
2.1 xylem • 2.2 phloem • 2.3 transpiration stream • 2.4 cohesion-tension • 2.5 translocation • 2.6 source • 2.7 sink • 2.8 Casparian strip • 2.9 stomata • 2.10 guard cells.
Q3, Organ function recall
Roote.g. epidermis + root hairs; absorbs water and minerals from soil; anchors plant in substrate.
Steme.g. vascular bundles; supports leaves in optimal light positions; transports xylem (water up) and phloem (sugars down).
Leafe.g. palisade mesophyll; primary site of photosynthesis; gas exchange via stomata.
Flowere.g. pollen (contains male gametes); reproduction, pollen production and ovule fertilisation; attracts pollinators.
Q4, True / false with correction
4.1 True.
4.2 False. Correction: the upper epidermis has no chloroplasts. Its flat transparent cells allow light to pass through to the palisade layer below without absorbing it, which would shade photosynthetic cells.
4.3 True.
4.4 False. Correction: in most plants stomata are more numerous on the lower (abaxial) surface. This reduces direct sun exposure of the open pores, lowering evaporative water loss while still permitting gas exchange.
4.5 True.
Q5, Sample concept map
A correct map should include arrows such as:
- xylemsupplies water to → palisade mesophyll
- palisade mesophyllexports sucrose via → phloem
- spongy mesophyllprovides air-space diffusion pathway for CO2 to reach → palisade mesophyll
- stomataallow CO2 to enter → spongy mesophyll
- guard cellscontrol opening and closing of → stomata
- palisade mesophyllproduces O2 that exits through → stomata
Any biologically valid linking phrases are accepted. Award full marks for at least 6 correctly labelled arrows that respect causal direction.