Plant Tissues, Organs and Systems¶
Part of 4.2 Organisation.
Plant organisation uses the same cell-to-tissue-to-organ pattern as animals, but the transport problems are different. Plants must move water, minerals and sugars without a pump like a heart.
Learning Objectives¶
| ID | Official specification wording | Main teaching sections |
|---|---|---|
4.2.3-lo-1 |
4.2.3.1 Students should be able to explain how the structures of plant tissues are related to their functions. 4.2.3.1 Plant tissues include: 4.2.3.1 • epidermal tissues 4.2.3.1 • palisade mesophyll 4.2.3.1 • spongy mesophyll 4.2.3.1 • xylem and phloem 4.2.3.1 • meristem tissue found at the growing tips of shoots and roots. 4.2.3.1 The leaf is a plant organ. Knowledge limited to epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata. |
Plant Tissues |
4.2.3-lo-2 |
4.2.3.2 Content Key opportunities Students should be able to explain how the structure of AT 3, 4, 5 root hair cells, xylem and phloem are adapted to their Measure the functions. 4.2.3.2 uptake of water. 4.2.3.2 Students should be able to explain the effect of AT 6, 7 changing temperature, humidity, air movement and Investigate the light intensity on the rate of transpiration. 4.2.3.2 guard cells. 4.2.3.2 Process data stomata and arithmetic means, of sampling and volumes. 4.2.3.2 Students should be able to understand and use simple MS 1a, 1c compound measures such as the rate of transpiration. 4.2.3.2 Students should be able to: MS 2c, 4a, 4c 4.2.3.2 • translate information between graphical and numerical form 4.2.3.2 • plot and draw appropriate graphs, selecting appropriate scales for axes |
Plant Organs and Transport |
4.2.3-lo-3 |
4.2.3.2 • extract and interpret information from graphs, charts and tables. 4.2.3.2 The roots, stem and leaves form a plant organ system for transport of substances around the plant. 4.2.3.2 Students should be able to describe the process of transpiration and translocation, including the structure and function of the stomata. 4.2.3.2 Root hair cells are adapted for the efficient uptake of water by osmosis, and mineral ions by active transport. 4.2.3.2 Xylem tissue transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream. 4.2.3.2 The role of stomata and guard cells are to control gas exchange and water loss. 4.2.3.2 Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food molecules through phloem tissue is called translocation. 4.2.3.2 Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls. 4.2.3.2 Detailed structure of phloem tissue or the mechanism of transport is not required. |
Plant Organs and Transport |
Plant Tissues¶
- Epidermal tissue covers the outside of the plant and helps reduce water loss through a waxy cuticle. The lower epidermis contains guard cells that control stomata.
- Palisade mesophyll is packed with chloroplasts and arranged in columns for photosynthesis, maximizing light absorption.
- Spongy mesophyll contains air spaces for gas exchange and is less densely packed, allowing CO₂ diffusion.
- Xylem carries water and mineral ions from the roots to the leaves, and consists of dead, hollow cells that form continuous tubes (vessels).
- Phloem carries dissolved sugars (from photosynthesis) around the plant in both directions depending on demand, using living cells with sieve tubes and companion cells.
- Meristem tissue contains unspecialised cells that keep dividing and allow the plant to keep growing throughout life (located at root tips, shoot tips and within stems).
Plant Organs and Transport¶
- Roots absorb water and mineral ions through root hair cells (which have large surface area), stems support the plant and connect transport tissues, and leaves are broad and thin to maximise light capture and gas exchange.
- Root hair cells use active transport to absorb mineral ions against the concentration gradient, and osmosis to absorb water.
- Transpiration is the loss of water vapour from leaves through the stomata. This evaporation creates water potential gradients that help pull water up the xylem from the roots in a process called the transpiration stream.
- Factors affecting transpiration: temperature (higher = faster), humidity (lower = faster), light intensity (higher = faster, more stomata open), and wind (faster, removes humid air).
- Translocation is the movement of dissolved sugars (and other solutes) in the phloem from sources (like photosynthetic leaves) to sinks (like growing tissues or storage areas). This is active transport, requiring energy.
- Leaves are adapted for photosynthesis and gas exchange: large surface area, thin (short diffusion distance), have vascular tissues, stomata for gas exchange, and palisade cells for photosynthesis.
Common Confusions¶
- Xylem vs. phloem: Xylem transports water and minerals upward only (from roots); phloem transports sugars in both directions. Xylem has dead cells forming tubes; phloem has living sieve tube elements.
- Transpiration vs. translocation: Transpiration is water loss (physical evaporation); translocation is sugar movement (active transport). They are different processes.
- Guard cells and stomata: Guard cells are the cells that control the stomata (pores). When turgid, they open the pore; when flaccid, they close it.
- Palisade vs. spongy mesophyll: Palisade cells are columnar and densely packed (photosynthesis); spongy cells are irregular and loosely arranged (gas exchange). Both are mesophyll.
Key Terms¶
- Xylem: plant tissue that transports water and mineral ions from the roots.
- Phloem: plant tissue that transports dissolved sugars around the plant.
- Transpiration: the loss of water vapour from plant leaves.
- Translocation: the movement of dissolved sugars through the phloem.
- Transpiration stream: the continuous upward movement of water from roots through xylem to leaves, driven by transpiration.
- Meristem: plant tissue containing cells that can divide and differentiate.
- Stoma: a pore in the leaf surface through which gases and water vapour move.
- Guard cell: specialized cell pair controlling the opening and closing of stomata.
- Palisade mesophyll: columnar photosynthetic tissue in the upper leaf.
- Spongy mesophyll: loosely arranged tissue in the lower leaf for gas exchange.
- Root hair cell: epidermal cell with large surface area for water and ion absorption.
- Vascular bundle: group of xylem and phloem tissues in roots, stems and leaves.