AQA Biology 4.2.3.1
Plant tissues and organs
A leaf is an organ: layers of tissue, each built for one job. Travel through it layer by layer, then find where a plant makes its new cells.
Combined Science · Higher tier
Start here
Turn a leaf over.
Pick a leaf from a tree or a hedge and look at it in daylight: first the side that faced the sky, then the side that faced the ground.
If you had to guess, which side is darker green?
The leaf · one organ, many tissues
Each layer is built for its job.
Leaves, stems and roots are plant organs. A leaf is made of several tissues working together. Step through them from top to bottom.
1 of 8 tissues visited
Waxy cuticle
Structure
A thin waxy, waterproof layer made by the epidermis.
So it can
Reduce water loss from the leaf.
In the vein · xylem and phloem
Water comes in. Sugar goes out.
Xylem
Carries water and dissolved mineral ions up from the roots to the leaves. Hollow tubes of dead cells, with walls strengthened by lignin.
Phloem
Carries dissolved sugars from the leaves to the rest of the plant. Tubes of living, elongated cells; cell sap moves from one cell to the next through pores in the end walls.
How water is pulled up the xylem, and how fast, is the transpiration lesson.
The fifth tissue · meristem
New cells, at the growing tips.
Meristem tissue is found at the growing tips of shoots and roots. It makes new cells, and these can differentiate into any type of plant cell, throughout the life of the plant.
So a plant keeps growing longer shoots and roots for as long as it lives.
Think again · which tube
“Xylem carries the food and phloem carries the water.”
Your call
ChooseSugar made in a leaf is carried down to the roots. Which tissue carries it?
Sort
Which tissue does the job?
Place each job with its tissue type.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Name
- The tissue, spelled right: palisade mesophyll, not just “palisade cells”.
- Explain
- Structure, then function: “many chloroplasts, so more light absorbed for photosynthesis.”
- Suggest
- Apply what a tissue does to a new situation.
Key fact
The leaf is a plant organ. Its tissues are the epidermis, palisade mesophyll, spongy mesophyll, xylem and phloem, with guard cells around the stomata. Meristem at shoot and root tips makes new cells.
Key note · AQA 4.2.3.1
Plant tissues and organs
- The leaf is a plant organ, made of several tissues.
- Epidermis: covers the leaf; makes a waxy cuticle that reduces water loss. Guard cells around the stomata control gas exchange and water loss.
- Palisade mesophyll: near the upper surface, packed with chloroplasts; most photosynthesis.
- Spongy mesophyll: air spaces for gases to diffuse.
- Xylem: water and mineral ions, hollow dead tubes, lignin. Phloem: dissolved sugars, living cells with pores in the end walls.
- Meristem, at the growing tips of shoots and roots, makes new cells that can become any type of plant cell.
Photograph this card. Tomorrow, cover it and say each line first.
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Mixing up xylem and phloem?
The leaf section and plant outline are schematic drawings, not to scale.