How are root hair cells, xylem, phloem and the leaf adapted to their functions?
Explain how root hair cells absorb water and mineral ions, how the structures of xylem and phloem are adapted to their function, and how the leaf is adapted for photosynthesis and gas exchange.
A focused answer to Edexcel GCSE Biology 6.7, 6.8 and 6.11B, covering how root hair cells are adapted to absorb water and ions, the structure and function of xylem and phloem, and how the leaf is adapted for photosynthesis and gas exchange.
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What this dot point is asking
Edexcel statements 6.7, 6.8 and 6.11B want you to explain how root hair cells are adapted to absorb water and mineral ions, how the structures of xylem and phloem suit their functions, and how the leaf is adapted for photosynthesis and gas exchange (6.11B is Biology only). The theme is structure related to function.
Root hair cells
Xylem and phloem
Plants have two transport tissues, and it is essential not to confuse them.
A memory hook: xylem carries water (think "x marks the water"), is dead and lignified, and goes one way; phloem carries food (sucrose), is alive, and goes both ways.
The leaf (Biology only)
The leaf is the main organ of photosynthesis, and its structure is adapted for the job:
- It is broad and flat to give a large surface area to capture light.
- It is thin, so gases diffuse in and out quickly and light reaches the inner cells.
- The palisade mesophyll near the upper surface is packed with chloroplasts to absorb light.
- The spongy mesophyll has air spaces that allow carbon dioxide and oxygen to diffuse between the cells.
- Stomata (pores) on the lower surface, opened and closed by guard cells, let carbon dioxide in and oxygen and water vapour out.
- A network of veins (xylem and phloem) supplies water and carries away the sugars made.
Try this
Q1. State which tissue carries water up the plant and which carries sugars around it. [2 marks]
- Cue. Xylem carries water (and mineral ions) up; phloem carries sugars (sucrose) around the plant.
Q2. Give one way a root hair cell is adapted to absorb water. [1 mark]
- Cue. Its long, thin shape gives a large surface area for absorbing water by osmosis.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksExplain how a root hair cell is adapted to absorb water and mineral ions from the soil.Show worked answer →
A 4-mark explain question rewards adaptations each linked to absorption.
- The root hair cell has a long, thin extension that gives it a large surface area, so more water and ions can be absorbed at once.
- Water enters by osmosis, down a water concentration gradient from the dilute soil water into the more concentrated cell.
- Mineral ions are absorbed by active transport against their concentration gradient, which needs energy.
- The cell has many mitochondria to release the energy for this active transport.
Markers reward the large surface area, osmosis for water, active transport for ions, and mitochondria providing energy. Saying the root hair simply soaks up water, without the mechanisms, scores little.
Edexcel 20214 marksCompare the structure and function of xylem and phloem.Show worked answer →
A 4-mark compare question rewards linked points about both tissues.
Xylem transports water and dissolved mineral ions from the roots up to the leaves in one direction only. It is made of dead, hollow cells strengthened by lignin, forming continuous tubes.
Phloem transports dissolved sugars (sucrose) made in the leaves to all parts of the plant, in both directions (translocation). It is made of living cells with sieve plates between them.
Markers reward what each transports, the direction, and the structural difference (dead lignified xylem versus living phloem with sieve plates). Mixing up which tissue carries water and which carries sugar loses marks.
Related dot points
- Explain how water and mineral ions are transported by transpiration including the role of stomata, how sucrose is moved by translocation, and the effect of environmental factors on the rate of water uptake.
A focused answer to Edexcel GCSE Biology 6.9, 6.10, 6.12 and 6.13, covering transpiration and the stomata, translocation of sucrose, the effect of light, temperature and air movement on water uptake, and rate calculations for transpiration.
- Describe photosynthesis as an endothermic reaction, explain the effect of temperature, light intensity and carbon dioxide as limiting factors, and use the inverse square law for light intensity.
A focused answer to Edexcel GCSE Biology 6.1 to 6.6, covering photosynthesis as an endothermic reaction, temperature, light intensity and carbon dioxide as limiting factors, the light-intensity core practical, and the inverse square law.
- Explain how plants are adapted to survive in extreme environments, how plant hormones such as auxins control growth in phototropisms and gravitropisms, and the commercial uses of plant hormones.
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- Explain how substances are transported into and out of cells by diffusion, osmosis and active transport, investigate osmosis in potatoes, and calculate the percentage change in mass.
A focused answer to Edexcel GCSE Biology 1.15 to 1.17, covering diffusion, osmosis and active transport, the osmosis core practical with potatoes, and how to calculate the percentage change in mass.
Sources & how we know this
- Pearson Edexcel GCSE (9-1) Biology (1BI0) specification — Pearson (2016)