Leaves
Biology: AQA GCSE Higher, topic 2.5.2
Leaves
Leaves are examples of plant organs made up of different types of tissue:
Epidermal tissue
- Epidermal tissue covers the outer surface of leaves (as well as the rest of the plant).
Palisade mesophyll
- Palisade mesophyll is a row of cells located below the upper epidermis.
- The cells are exposed to a lot of sunlight.
- The cells have lots of chloroplasts (where photosynthesis takes place) to maximise the energy transfer in photosynthesis.
Spongy mesophyll
- Spongy mesophyll contains many air spaces, which help with gas exchange throughout the leaf.
Stomata
- Found in the lower epidermis, these gaps facilitate (make easier) the diffusion of gases in and out of the leaf, if they are open.
- When necessary, specialised (perform a specific function) guard cells are capable of closing these gaps.
- e.g. in hot weather to reduce water loss.
Test yourself on Leaves
Why do guard cells close the stomata during hot weather?
Why is palisade mesophyll located directly below the upper epidermis of a leaf?
How do spongy mesophyll and stomata work together to allow gas exchange in a leaf?
Why does a leaf need both palisade mesophyll and spongy mesophyll?
Why does the lower epidermis need stomata, even though epidermal tissue already covers the leaf's surface?