Structure of a leaf
Feature Function Large surface area To maximise light absorption Thin Short distance for carbon dioxide to diffuse into leaf cells Thin (transparent) epidermis Allows light to reach the palisade cells Thin waxy cuticle Protects the leaves without blocking out light The
cells found in the palisade layer have many CHLOROPLASTS which contain lots of CHLOROPHYLL. This
is the place where PHOTOSYNTHESIS take place.
The spongy and palisade layers have many air spaces to allow CO 2 to reach the
palisade cell so that it can be used during photosynthesis.
To limit water loss, the epidermal
cells make wax which cover the leaf,
especially the top surface.
The
bottom part of the leaf is full of tiny little pores called STOMATA.
They allow CO 2 to enter and O2 to exit the leaf.
They also let water to escape - this is called TRANSPIRATION.
XYLEM and PHLOEM tubes, 'like
veins', cover the entire leaf. They transport water to every part of the leaf and carry away the food made by the leaf.
Each stoma is surrounded by a pair of sausage
shaped GUARD
CELLS.
They control
the opening and closing of the stoma.
Stoma closes
automatically when supply of water from the roots becomes scarce.
When there is very
little water the Guard Cells become FLACCID,
resulting in change of their shape and closing of stomatal pores.
When
stomata are closed, no water is lost. However, this also stops any CO 2 entering the leaf, thus stopping PHOTOSYNTHESIS.
Remember:
The
sole purpose of the leaf is to make food by PHOTOSYNTHESIS. Leaves are adapted to obtain carbon dioxide, water
Features of leaves and their functions
Remember:
STOMATA - (singular: stoma,
a tiny pore in the leaf)
Test your understanding of how the different parts of a leaf are adapted for their jobs. 1. Which layer of the leaf contains the most chloroplasts for photosynthesis? 2. What is the main function of the waxy cuticle found on the upper surface of the leaf? 3. Through which tiny pores on the underside of the leaf do gases like carbon dioxide enter? 4. Which specialized cells control the opening and closing of the stomata? 5. Why does the spongy mesophyll layer contain large air spaces? 🔬 Knowledge Check: Leaf Structure
Click to Reveal Answers
2. To reduce water loss by evaporation (It acts as a waterproof barrier).
3. Stomata (These pores facilitate gas exchange).
4. Guard cells (They swell and shrink to open and close the stomatal pores).
5. To allow gases to diffuse easily (Air spaces let carbon dioxide reach the palisade cells and oxygen to escape).