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Ordinary Level Revision Notes
Leaving Cert Ordinary Level Biology
Chapter 13: Plant Anatomy, Transport and Responses
Transport + Plant Coordination
Subtopics Covered
- Learning Outcomes
- Big Picture: Plants Must Transport and Respond
- Plant Tissue Systems
- Xylem vs Phloem
- Roots, Stems and Leaves: Tissue Locations
- Monocotyledons vs Dicotyledons
What This Pack Includes
- Structured chapter notes formatted for ExamsLogic website reading
- Exam-focused diagrams, definitions, and worked examples
- Interactive practice sections carried over from the source notes
- Independent study guidance based on the official curriculum
- Print-friendly layout for future PDF export when needed
This publication is an independent educational resource developed by ExamsLogic and compiled by experienced educators. It is based on publicly available official curricula, including Cambridge, Pearson Edexcel, IB, and the Irish Leaving Certificate. This product is not endorsed by, affiliated with, or sponsored by any examination board or governing authority. All registered trademarks remain the property of their respective owners.
1. Learning Outcomes
- Identify dermal, vascular and ground tissues in plants.
- Compare xylem and phloem in structure and function.
- Describe plant structures in roots, stems and leaves.
- Compare monocotyledons and dicotyledons.
- Explain water absorption by root hair cells.
- Describe water movement through xylem vessels.
- Explain transpiration and transpiration pull using the Dixon-Joly Cohesion-Tension model at OL-friendly depth.
- Describe how stomata open and close.
- Explain auxins/IAA as plant growth regulators.
- Describe phototropism, geotropism and thigmotropism.
OL Focus: Learn the diagrams and the direction of transport. Plant transport questions often reward clear labels and simple cause-and-effect explanations.
2. Big Picture: Plants Must Transport and Respond
Support
Plant tissues give strength and protection so plants can stand upright and survive damage.
Transport
Xylem carries water and minerals, while phloem carries food made by photosynthesis.
Response
Plants respond to light, gravity and touch using growth regulators such as auxins.
Biology link: Leaves make food, roots absorb water, stems connect them, and hormones help the plant grow in useful directions.
3. Plant Tissue Systems
| Tissue system | Main role | Examples / location |
|---|---|---|
| Dermal tissue | Protection and control of exchange with the environment. | Epidermis, cuticle, root hairs, stomata. |
| Vascular tissue | Transport of materials. | Xylem and phloem in roots, stems and leaves. |
| Ground tissue | Photosynthesis, storage and support. | Mesophyll in leaves, cortex and pith in stems/roots. |
Exam Tip: Dermal = covering/protection. Vascular = transport. Ground = filling tissue, storage, photosynthesis and support.
4. Xylem vs Phloem
| Feature | Xylem | Phloem |
|---|---|---|
| Main substance transported | Water and dissolved mineral ions. | Sugars/food made by photosynthesis. |
| Direction | Mainly upward from roots to leaves. | Both directions depending on plant needs. |
| Cells | Dead hollow vessels at maturity. | Living tissue, including sieve tubes and companion cells. |
| Extra role | Provides support due to lignin. | Translocation of food. |
| Wall | Thick, strengthened with lignin. | Less thick; sieve plates allow flow. |
Examiner Trap: Xylem is not for glucose transport. Glucose/sucrose transport is phloem.
5. Roots, Stems and Leaves: Tissue Locations
| Plant organ | Important tissues | Function |
|---|---|---|
| Root | Epidermis with root hairs, cortex, xylem, phloem. | Absorbs water/minerals and transports them upward. |
| Stem | Vascular bundles containing xylem and phloem, ground tissue. | Supports plant and transports materials. |
| Leaf | Epidermis, mesophyll, veins, stomata. | Photosynthesis, gas exchange and transpiration. |
6. Monocotyledons vs Dicotyledons
| Feature | Monocotyledon | Dicotyledon |
|---|---|---|
| Seed leaves/cotyledons | One cotyledon. | Two cotyledons. |
| Leaf veins | Usually parallel veins. | Usually net-like veins. |
| Flower parts | Often in multiples of 3. | Often in multiples of 4 or 5. |
| Root system | Often fibrous roots. | Often tap root system. |
| Vascular bundles in stem | Scattered. | Often arranged in a ring. |
Exam Tip: For quick identification, leaf veins are very useful: monocot = parallel, dicot = net-like.
7. Root Hair Absorption
Root hair cells are adapted for absorbing water and mineral ions from the soil.
| Adaptation | How it helps |
|---|---|
| Long root hair projection | Increases surface area for absorption. |
| Thin cell wall | Short diffusion distance. |
| Large vacuole | Helps maintain water uptake by osmosis. |
| Many mitochondria | Supply energy for active transport of mineral ions. |
Examiner Secret: Water enters root hair cells by osmosis. Mineral ions often enter by active transport.
8. Water Movement Through the Plant
Water moves from the soil into root hair cells, across the root, into xylem vessels, and upward to the leaves.
Soil water→
Root hair cell→
Root cortex→
Xylem→
Leaf cells→
Stomata
| Stage | Explanation |
|---|---|
| Absorption | Water enters root hair cells by osmosis. |
| Movement across root | Water moves from cell to cell and into xylem. |
| Transport in xylem | Water moves upward through hollow xylem vessels. |
| Loss from leaf | Water evaporates from leaf cells and diffuses out through stomata. |
Examiner Trap: Transpiration is water loss from aerial parts of plants, mainly leaves, not water absorption by roots.
9. Transpiration and Transpiration Pull
Transpiration is the loss of water vapour from a plant, mainly through stomata in leaves.
Transpiration pull helps draw water upward through the xylem from roots to leaves.
| Dixon-Joly Cohesion-Tension idea | OL-friendly explanation |
|---|---|
| Cohesion | Water molecules stick to each other. |
| Tension | Water loss from leaves creates a pulling force. |
| Continuous column | Because water molecules stick together, the pull moves water upward through xylem. |
Exam Tip: For transpiration pull, mention evaporation from leaves, water vapour leaving stomata, and water being pulled up xylem.
10. Factors Affecting Transpiration
| Factor | Effect on transpiration | Reason |
|---|---|---|
| High temperature | Increases transpiration. | Faster evaporation. |
| Wind | Increases transpiration. | Removes humid air near leaf surface. |
| Low humidity | Increases transpiration. | Steeper water vapour gradient. |
| High light intensity | Often increases transpiration. | Stomata open for photosynthesis. |
Common Mistake: Saying humid air increases transpiration. High humidity usually decreases transpiration because the air already contains much water vapour.
11. Stomata and Guard Cells
Stomata are pores usually found mainly on the lower surface of leaves. Each stoma is controlled by two guard cells.
| Condition | Guard cells | Stoma | Importance |
|---|---|---|---|
| Guard cells turgid | Filled with water and swollen. | Open. | Allows gas exchange for photosynthesis. |
| Guard cells flaccid | Lose water and become less swollen. | Closed. | Reduces water loss. |
Examiner Secret: Stomata balance two needs: allowing gas exchange and reducing water loss.
12. Plant Growth Regulators: Auxins / IAA
Auxins, including IAA, are plant growth regulators. They affect cell elongation and help control plant growth responses.
| Auxin fact | Meaning |
|---|---|
| Produced in shoot tips | Helps control shoot growth. |
| Moves away from light | Auxin builds up on the shaded side of shoots. |
| Stimulates shoot cell elongation | The shaded side grows more, so the shoot bends toward light. |
| Affects roots differently | High auxin can inhibit root elongation. |
Examiner Trap: In shoots, auxin usually causes more elongation. In roots, high auxin can reduce elongation. Do not treat roots and shoots as identical.
13. Phototropism
Phototropism is a plant growth response to light.
Shoots show positive phototropism: they grow toward light.
| Step | Explanation |
|---|---|
| Light from one side | Auxin moves to the shaded side of the shoot. |
| More auxin on shaded side | Cells on shaded side elongate more. |
| Unequal growth | The shoot bends toward the light. |
Exam Tip: Phototropism answers need three ideas: light direction, auxin distribution, unequal growth.
14. Geotropism / Gravitropism
Geotropism, also called gravitropism, is a plant growth response to gravity.
| Plant part | Response | Why useful? |
|---|---|---|
| Root | Positive geotropism: grows toward gravity/downward. | Anchorage and water/mineral absorption. |
| Shoot | Negative geotropism: grows away from gravity/upward. | Reaches light for photosynthesis. |
Examiner Secret: “Positive” means growth toward the stimulus. “Negative” means growth away from the stimulus.
15. Thigmotropism
Thigmotropism is a plant growth response to touch.
| Example | Explanation |
|---|---|
| Climbing plant tendrils | Tendrils coil around a support after touching it. |
| Advantage | Helps the plant climb and reach more light. |
Exam Tip: Tropisms are growth responses, not quick muscle-like movements.
16. Tropism Summary Table
| Tropism | Stimulus | Positive example | Negative example |
|---|---|---|---|
| Phototropism | Light | Shoots grow toward light. | Some roots may grow away from light. |
| Geotropism / gravitropism | Gravity | Roots grow downward. | Shoots grow upward away from gravity. |
| Thigmotropism | Touch | Tendrils grow/coiling toward support. | Less commonly examined at OL. |
17. Interactive Simulator: Transport Tissue Detective
Identify the Tissue
Clue: Transports water and minerals mainly upward.
Feedback
Ready
Think about transport direction and material carried.
18. Interactive Simulator: Tropism Detective
Identify the Tropism
Clue: A shoot bends toward light.
Feedback
Ready
Identify the stimulus: light, gravity or touch.
19. High-Value Exam Guidance
Exam Tip 1: Xylem carries water and minerals; phloem carries food/sugars.
Exam Tip 2: Root hairs are adapted by large surface area and thin walls.
Exam Tip 3: Transpiration pull depends on water loss from leaves.
Exam Tip 4: For phototropism, mention auxin and unequal growth.
Examiner Trap 1: Do not say stomata are always open. They open and close depending on conditions.
Examiner Trap 2: Do not mix up positive and negative tropism. Positive means toward stimulus.
Examiner Trap 3: Monocot and dicot comparisons must use matched features.
Common Mistake 1: Saying transpiration is water moving into roots. It is water loss from leaves.
Common Mistake 2: Saying phloem only moves upward. Phloem can move substances in both directions.
Examiner Secret 1: In stomata questions, use the words turgid and flaccid.
Examiner Secret 2: Auxin collects on the shaded side of shoots, causing that side to grow faster.
Examiner Secret 3: Dixon-Joly at OL can be explained as cohesion between water molecules plus tension from transpiration pull.
20. MCQs with Instant Answers
1. Xylem transports:
Answer: B. Xylem transports water and dissolved mineral ions.
2. Phloem transports:
Answer: A. Phloem transports food such as sugars made in photosynthesis.
3. Water enters root hair cells mainly by:
Answer: A. Water enters root hair cells by osmosis.
4. Transpiration is:
Answer: A. Transpiration is the loss of water vapour, mainly through stomata.
5. Guard cells control:
Answer: A. Guard cells control whether stomata open or close.
6. Shoots growing toward light show:
Answer: A. Growth toward light is positive phototropism.
7. Roots usually show:
Answer: A. Roots grow downward toward gravity, so they show positive geotropism.
8. Tendrils coiling around a support show:
Answer: A. Thigmotropism is growth response to touch.
9. Monocot leaves usually have:
Answer: A. Monocot leaves usually have parallel veins.
10. Auxin in shoots usually causes:
Answer: A. Auxin promotes cell elongation in shoots.
21. Structured Exam Questions
- Name the three plant tissue systems and state one function of each. [6]
- Compare xylem and phloem under four headings. [8]
- Draw and label a simple leaf cross section. [6]
- Compare monocotyledons and dicotyledons using four features. [8]
- Describe how a root hair cell is adapted for absorption. [6]
- Outline the pathway of water from soil to leaf air spaces. [6]
- Explain transpiration pull using the Dixon-Joly Cohesion-Tension idea. [6]
- Describe how stomata open and close. [5]
- Explain how auxin causes a shoot to bend toward light. [6]
- Compare phototropism, geotropism and thigmotropism. [6]
22. Detailed Mark Scheme
Q1. Dermal tissue: protection/exchange [2]. Vascular tissue: transport/xylem and phloem [2]. Ground tissue: photosynthesis/storage/support [2].
Q2. Xylem transports water/minerals [1], mainly upward [1], dead hollow vessels [1], lignin/support [1]. Phloem transports sugars/food [1], can move both directions [1], living tissue [1], translocation [1].
Q3. Correct leaf outline/layers [1]. Labels: upper epidermis/cuticle [1], palisade mesophyll [1], spongy mesophyll [1], vascular bundle/vein [1], lower epidermis/stoma/guard cells [1].
Q4. Monocot: one cotyledon [1], parallel veins [1], flower parts in 3s [1], scattered vascular bundles/fibrous roots [1]. Dicot: two cotyledons [1], net veins [1], flower parts in 4s/5s [1], vascular bundles in ring/tap root [1].
Q5. Root hair gives large surface area [1]. Thin wall/short diffusion distance [1]. Large vacuole [1]. Water enters by osmosis [1]. Mineral ions by active transport [1]. Mitochondria provide energy [1].
Q6. Soil water [1] enters root hair by osmosis [1], moves across cortex [1], enters xylem [1], moves up stem [1], reaches leaf mesophyll/air spaces [1].
Q7. Water evaporates from leaf cells [1]. Water vapour diffuses out through stomata [1]. This creates tension/pull [1]. Water molecules cohere/stick together [1]. Continuous water column in xylem [1]. Water is pulled upward from roots [1].
Q8. Guard cells control stomata [1]. When turgid they curve/open stoma [2]. When flaccid they close stoma [1]. This balances gas exchange and water loss [1].
Q9. Light from one side [1]. Auxin moves/builds on shaded side [1]. Auxin stimulates shoot cell elongation [1]. Shaded side grows faster [1]. Unequal growth causes bending [1]. Shoot bends toward light/positive phototropism [1].
Q10. Phototropism is response to light [2]. Geotropism is response to gravity [2]. Thigmotropism is response to touch [2]. Accept examples such as shoots to light, roots downward, tendrils coiling.
Q2. Xylem transports water/minerals [1], mainly upward [1], dead hollow vessels [1], lignin/support [1]. Phloem transports sugars/food [1], can move both directions [1], living tissue [1], translocation [1].
Q3. Correct leaf outline/layers [1]. Labels: upper epidermis/cuticle [1], palisade mesophyll [1], spongy mesophyll [1], vascular bundle/vein [1], lower epidermis/stoma/guard cells [1].
Q4. Monocot: one cotyledon [1], parallel veins [1], flower parts in 3s [1], scattered vascular bundles/fibrous roots [1]. Dicot: two cotyledons [1], net veins [1], flower parts in 4s/5s [1], vascular bundles in ring/tap root [1].
Q5. Root hair gives large surface area [1]. Thin wall/short diffusion distance [1]. Large vacuole [1]. Water enters by osmosis [1]. Mineral ions by active transport [1]. Mitochondria provide energy [1].
Q6. Soil water [1] enters root hair by osmosis [1], moves across cortex [1], enters xylem [1], moves up stem [1], reaches leaf mesophyll/air spaces [1].
Q7. Water evaporates from leaf cells [1]. Water vapour diffuses out through stomata [1]. This creates tension/pull [1]. Water molecules cohere/stick together [1]. Continuous water column in xylem [1]. Water is pulled upward from roots [1].
Q8. Guard cells control stomata [1]. When turgid they curve/open stoma [2]. When flaccid they close stoma [1]. This balances gas exchange and water loss [1].
Q9. Light from one side [1]. Auxin moves/builds on shaded side [1]. Auxin stimulates shoot cell elongation [1]. Shaded side grows faster [1]. Unequal growth causes bending [1]. Shoot bends toward light/positive phototropism [1].
Q10. Phototropism is response to light [2]. Geotropism is response to gravity [2]. Thigmotropism is response to touch [2]. Accept examples such as shoots to light, roots downward, tendrils coiling.
23. Mastery Checklist
- I can name dermal, vascular and ground tissues.
- I can compare xylem and phloem accurately.
- I can identify tissues in roots, stems and leaves.
- I can compare monocotyledons and dicotyledons.
- I can describe root hair cell adaptations.
- I can explain water absorption by osmosis.
- I can trace the pathway of water through xylem.
- I can define transpiration.
- I can explain transpiration pull using cohesion and tension.
- I can describe stomatal opening and closing.
- I can explain auxin/IAA action in shoots.
- I can distinguish phototropism, geotropism and thigmotropism.
- I can answer plant transport and response questions using clear diagrams.