AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
The leaf is a plant organ. Knowledge limited to epidermis, palisade and…
Full specification wording
Plant tissues: The leaf is a plant organ. Knowledge limited to epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata.
An organ is a group of tissues working together to carry out a function, and the leaf is the plant organ specialised for photosynthesis.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 3
Study notes
From the checked teaching notes for this specification point.
The idea
An organ is a group of tissues working together to carry out a function, and the leaf is the plant organ specialised for photosynthesis. Its upper and lower epidermis protect the leaf and reduce water loss through the waxy cuticle. Palisade mesophyll sits near the upper surface, where its many chloroplasts absorb light. Spongy mesophyll has air spaces that allow carbon dioxide to diffuse to the photosynthetic cells. Xylem delivers water and mineral ions, while phloem removes dissolved sugars. Guard cells surround stomata and change shape to open or close the pore, controlling gas exchange and water loss. Explaining the leaf as an organ means showing how these tissues cooperate, for example carbon dioxide entering through a stoma diffusing through spongy mesophyll to a palisade cell.
What earns the marks
- The leaf is an organ because several tissues work together to carry out photosynthesis.
- Epidermal tissue protects the leaf and its waxy cuticle reduces water loss; stomata in the epidermis allow gases to enter and leave.
- Palisade mesophyll contains chloroplasts and is positioned near the upper surface to absorb light for photosynthesis.
- Spongy mesophyll has air spaces that allow carbon dioxide to diffuse through the leaf to the palisade cells.
- Xylem supplies water and mineral ions to leaf cells, and phloem transports dissolved sugars away from the leaf.
- Guard cells surround stomata and open or close the pore, balancing gas exchange with the need to limit water loss.
Common mistakes and how to put them right
Describing the leaf as a tissue.
Put it right: The leaf is an organ made of several tissues working together.
Saying stomata are cells.
Put it right: Stomata are pores, and the guard cells are the cells that surround and control each pore.
Stating that guard cells only open stomata.
Put it right: They can also close the pore to reduce water loss.
Exam tips
- When explaining why the leaf is an organ, name at least two tissues and state how their functions combine.
- Use the terms epidermis, palisade mesophyll, spongy mesophyll, xylem, phloem and guard cells accurately in labelled diagrams and written answers.
- Link stomatal opening and closing to both gas exchange and water loss to show balanced understanding.
Try the lesson
The start of the Plant tissues: The leaf is a plant organ. Knowledge limited to epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata. lesson, made from checked teaching notes for this specification point.
Have a go first
Which tissue in a leaf forms a transparent outer layer that allows light to pass through to the photosynthetic cells?
Listen
An organ is a group of tissues working together to carry out a function, and the leaf is the plant organ specialised for photosynthesis. Its upper and lower epidermis protect the leaf and reduce water loss through the waxy cuticle. Palisade mesophyll sits near the upper surface, where its many chloroplasts absorb light. Spongy mesophyll has air spaces that allow carbon dioxide to diffuse to the photosynthetic cells. Xylem delivers water and mineral ions, while phloem removes dissolved sugars. Guard cells surround stomata and change shape to open or close the pore, controlling gas exchange and water loss. Explaining the leaf as an organ means showing how these tissues cooperate, for example carbon dioxide entering through a stoma diffusing through spongy mesophyll to a palisade cell. A strong answer earns marks for these points. The leaf is an organ because several tissues work together to carry out photosynthesis. Epidermal tissue protects the leaf and its waxy cuticle reduces water loss; stomata in the epidermis allow gases to enter and leave. Palisade mesophyll contains chloroplasts and is positioned near the upper surface to absorb light for photosynthesis. Spongy mesophyll has air spaces that allow carbon dioxide to diffuse through the leaf to the palisade cells. A common slip: Describing the leaf as a tissue. Instead, the leaf is an organ made of several tissues working together. Exam tip: When explaining why the leaf is an organ, name at least two tissues and state how their functions combine.
See it
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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