How is a leaf built for photosynthesis, and how do xylem and phloem transport substances around a plant?
The structure of a leaf and how it is adapted for photosynthesis, and the structure and function of the xylem and phloem in transporting water, minerals and sugars.
A focused answer to the WJEC GCSE Biology section 1.5 topic on leaf structure and plant transport, covering the structure of a leaf and its adaptations for photosynthesis, the structure and function of xylem and phloem, and the uptake of water by root hair cells.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
WJEC wants you to describe the structure of a leaf and explain how it is adapted for photosynthesis, and to describe the structure and function of the xylem and phloem and the uptake of water by root hair cells.
The structure of a leaf
A leaf is organised in layers, each suited to its job.
- Waxy cuticle: a waterproof layer on top that reduces water loss.
- Upper epidermis: a thin, transparent layer that lets light through to the cells below.
- Palisade mesophyll: tightly packed cells near the top, full of chloroplasts, where most photosynthesis happens.
- Spongy mesophyll: loosely packed cells with air spaces that allow gases (carbon dioxide and oxygen) to move to and from the cells.
- Stomata: small pores, mostly on the lower surface, that let carbon dioxide diffuse in and oxygen and water vapour diffuse out.
- Guard cells: surround each stoma and open or close it to control gas exchange and water loss.
- Vascular bundles: contain the xylem and phloem (the veins of the leaf).
How the leaf is adapted for photosynthesis
Each feature of the leaf helps it photosynthesise efficiently.
- Broad and flat: a large surface area to absorb as much light as possible.
- Thin: gases and light reach the cells over a short distance.
- Many chloroplasts in the palisade layer: positioned near the top to absorb the most light.
- Air spaces in the spongy layer: let carbon dioxide reach the photosynthesising cells.
- Stomata and guard cells: allow carbon dioxide in while controlling water loss.
Transport in plants
Plants have two transport tissues, which carry different substances in different directions.
- Xylem: made of dead, hollow cells joined into long tubes, strengthened with a substance called lignin. It carries water and minerals upwards only, and its strength helps support the plant.
- Phloem: made of living cells. It carries dissolved sugars from the leaves (the source) to where they are used or stored (the sinks, such as the roots and growing tips). This can go up or down the plant.
Uptake of water by root hair cells
Water enters the plant through the root hair cells. Each has a long, thin extension that gives a large surface area for absorbing water by osmosis and mineral ions by active transport. The water then passes into the xylem and travels up to the leaves.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksDescribe two ways the structure of a leaf is adapted for photosynthesis.Show worked answer →
A 4-mark question: two adaptations, each linked to photosynthesis, with a fourth mark for clear links.
The leaf is broad and flat, giving a large surface area to absorb as much light as possible. The palisade mesophyll cells near the top are packed with chloroplasts to trap the most light. The leaf is thin so gases and light reach the cells easily, and it has stomata on the lower surface that let carbon dioxide diffuse in.
Markers reward: large surface area for light; many chloroplasts in the palisade layer; stomata for carbon dioxide; thin for short diffusion. Naming a feature without saying how it helps photosynthesis does not gain the mark.
WJEC style4 marksCompare the function of the xylem and the phloem in a plant.Show worked answer →
A 4-mark compare question.
The xylem carries water and dissolved mineral ions from the roots up to the leaves; this movement is in one direction (upwards) and the xylem also supports the plant. The phloem carries dissolved sugars (such as sucrose) made in the leaves to other parts of the plant, such as the roots and growing tips; this movement is called translocation and can go in either direction.
Markers reward: xylem carries water and minerals from roots to leaves; phloem carries sugars from leaves to the rest of the plant (translocation). Saying both carry water, or mixing up which carries sugar, are common errors.
Related dot points
- Photosynthesis as the process that makes glucose using light energy, its word and symbol equations, the limiting factors of light, carbon dioxide and temperature, and the required practicals.
A focused answer to the WJEC GCSE Biology section 1.5 topic on photosynthesis, covering photosynthesis as the process that uses light energy to make glucose, its word and symbol equations, the limiting factors of light intensity, carbon dioxide and temperature, and the required practicals on starch production and rate.
- Transpiration as the loss of water vapour from a plant, the transpiration stream, the factors that affect the rate of transpiration, and the role of stomata and guard cells.
A focused answer to the WJEC GCSE Biology section 1.5 topic on transpiration, covering transpiration as the loss of water vapour from a plant, the transpiration stream, the factors affecting its rate, and the role of stomata and guard cells in controlling water loss.
- Feeding relationships in ecosystems, food chains and food webs, pyramids of number and biomass, the transfer of energy along a food chain and why energy is lost at each trophic level.
A focused answer to the WJEC GCSE Biology section 1.6 topic on feeding relationships, covering food chains and food webs, pyramids of number and biomass, the transfer of energy along a food chain, why energy is lost at each trophic level, and the implications for food production.
- The carbon cycle and the nitrogen cycle, the roles of photosynthesis, respiration, combustion and decomposition, the types of bacteria in the nitrogen cycle, and the conditions affecting decay.
A focused answer to the WJEC GCSE Biology section 1.6 topic on nutrient cycles, covering the carbon cycle and the roles of photosynthesis, respiration, combustion and decomposition, the nitrogen cycle and its bacteria, the role of decomposers, and the conditions that affect the rate of decay.
Sources & how we know this
- WJEC GCSE Biology specification (from 2016) — WJEC (2016)