Plant Tissues
Recap Plant Tissues for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Link each plant tissue to its job, from the palisade mesophyll packed with chloroplasts to the xylem and phloem that transport water and food.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Plants have tissues organised into organs, just as animals do. The leaf, stem and root are all plant organs, and together they form the plant organ system for transport.
The leaf contains several tissues. The upper epidermis is transparent to let light through, the palisade mesophyll contains most of the chloroplasts for photosynthesis, and the spongy mesophyll has air spaces allowing gases to diffuse.
The xylem and phloem run through the plant. Xylem carries water and mineral ions upwards from the roots. Phloem carries dissolved sugars both up and down the plant in a process called translocation. The lower epidermis contains stomata and guard cells controlling gas exchange and water loss.
Revision notes
Leaf tissues
Upper epidermis: transparent so light can pass through to the cells below. Palisade mesophyll: packed with chloroplasts, the main site of photosynthesis.
Spongy mesophyll: contains air spaces so carbon dioxide can diffuse to the cells. Lower epidermis: contains stomata for gas exchange.
Xylem and phloem
Xylem: hollow dead tubes strengthened with lignin, carrying water and mineral ions from the roots upwards only.
Phloem: living tissue with sieve plates, carrying dissolved sugars both upwards and downwards. This movement is called translocation.
Stomata and guard cells
Stomata are pores, mostly on the lower surface of the leaf, that allow carbon dioxide in and oxygen and water vapour out.
Guard cells surround each stoma and change shape to open or close it, controlling gas exchange and water loss.
Key points
- The leaf, stem and root are plant organs.
- Palisade mesophyll contains most of the chloroplasts.
- Spongy mesophyll has air spaces for gas diffusion.
- Xylem carries water and mineral ions upwards.
- Phloem carries dissolved sugars in both directions.
- Guard cells control the opening of stomata.
Worked examples
Example 1
Explain why most chloroplasts are found in the palisade mesophyll. [2 marks]
Model answer
The palisade mesophyll is near the top of the leaf where most light reaches (1 mark), so having chloroplasts there maximises the rate of photosynthesis (1 mark).
Example 2
State two differences between xylem and phloem. [2 marks]
Model answer
Xylem carries water and mineral ions, whereas phloem carries dissolved sugars (1 mark). Xylem cells are dead and carry substances upwards only, whereas phloem cells are living and carry substances in both directions (1 mark).
Example 3
Explain the function of guard cells. [2 marks]
Model answer
Guard cells surround each stoma and change shape to open or close it (1 mark), controlling gas exchange and limiting water loss from the leaf (1 mark).
Common mistakes
Confusing xylem and phloem.
Xylem is dead and carries water upwards; phloem is living and carries sugars both ways.
Saying stomata are on the upper surface.
Most are on the lower surface, which reduces water loss.
Calling the leaf a tissue.
The leaf is an organ containing several different tissues.
Forgetting that spongy mesophyll has air spaces.
The air spaces are what allow carbon dioxide to diffuse to the photosynthesising cells.
Exam tips
- Learn the leaf tissues in order from upper to lower surface.
- Give the direction of transport when comparing xylem and phloem.
- Link each tissue to its function.
- Remember stomata are mostly on the lower surface.
Key terms
- Palisade mesophyll
- The leaf tissue containing most chloroplasts.
- Stoma
- A pore in the leaf allowing gas exchange.
- Translocation
- The movement of dissolved sugars through the phloem.
- Guard cell
- A cell controlling the opening and closing of a stoma.
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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.