Structure of a leaf

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.