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Plant Tissues (AQA GCSE Biology: Combined Science)
Revision Note
Plant tissue: structures & functions
- The structures of plant tissues are related to their functions
- Some important plant tissues include:
- epidermal tissues
- palisade mesophyll
- spongy mesophyll
- xylem and phloem
- meristem tissue found at the growing tips of shoots and roots
Leaf structures table
| Structure | Description |
| Waxy cuticle | Protective layer on top of the leaf, prevents water from evaporating |
| Upper epidermis | Thin and transparent to allow light to enter palisade mesophyll layer underneath it |
| Palisade mesophyll | Column shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis |
| Spongy mesophyll | Contains internal air spaces that increases the surface area to volume ratio for the diffusion of gases (mainly carbon dioxide) |
| Lower epidermis | Contains guard cells and stomata |
| Guard cells | Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in, oxygen to diffuse out |
| Stomata |
Where gas exchange takes place Opens during the day, closes during the night, evaporation of water also takes places from here In most plants, found in much greater concentration on the underside of the leaf to reduce water loss |
| Vascular bundle | Contains xylem and phloem to transport substances to and from the leaf |
| Xylem | Transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata |
| Phloem | Transports sucrose and amino acids around the plant |
The leaf
- The leaf is a plant organ adapted specifically for photosynthesis
- You should be able to observe and draw of a transverse section of a leaf
Diagram showing the cross-section of a leaf
Adaptations of the leaf table
| Feature | Adaptation |
| Large surface area (leaf) | Increases surface area for the diffusion of carbon dioxide and absorption of light for photosynthesis |
| Thin | Allows carbon dioxide to diffuse to palisade mesophyll cells quickly |
| Chlorophyll | Absorbs light energy so that photosynthesis can take place |
| Network of veins | Allows the transport of water to the cells of the leaf and carbohydrates from the leaf for photosynthesis (water for photosynthesis, carbohydrates as a product of photosynthesis) |
| Stomata | Allows carbon dioxide to diffuse into the leaf and oxygen to diffuse out |
| Epidermis is thin and transparent | Allows more light to reach the palisade cells |
| Thin cuticle made of wax | To protect the leaf without blocking sunlight |
| Palisade layer at the top of the leaf | Maximises the absorption of light as it will hit chloroplasts in the cells directly |
| Air spaces in the spongy layer | Air spaces allow carbon dioxide to diffuse through the leaf, increasing the surface area |
| Vascular bundle | Thick cell walls of the tissue in the bundles help to support the stem and leaf |
- The structure of a leaf maximises the diffusion of carbon dioxide into the mesophyll cells for photosynthesis:
The structure of a leaf enables air to circulate within it to maximise the diffusion of carbon dioxide to the chloroplasts for photosynthesis
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