The Leaf

Being the main food-making organ in plants, leaves are often green in colour as they contain a lot of chlorophyll. The veins seen on a leaf are used to support the leaf. In these veins, there are vascular bundles which contain xylem vessels as well as phloem which carry substances to and from the leaf. The diagram below shows what is seen when the cross-section of a leaf is viewed under a microscope.

TRANSVERSE SECTION THROUGH PART OF A LEAF

Functions of parts of the leaf

Epidermis– protects the inner layers of cells in the leaf. It does not contain chloroplasts. The cells of the upper epidermis often secretes a waxy substance (cuticle) that stops water from evaporating from the leaf. Sometimes a cuticle is present on the under-side of the leaf.

Stomata– singular stoma, these are small holes on the leaf that are surrounded by guard cells. These holes open or close depending on the position of the guard cells which are ‘sausage shaped’. The guard cells contain chloroplasts.

Mesophyll– these cells make up the middle layer of the leaf. (meso- middle, phyll- leaf). These cells all contain chlorophyll.

-Palisade layer– these cells are closer to the top of the leaf and are arranged like a fence/ palisade.

-Spongy layer– these cells are below the palisades and are more round and arranged loosely with air spaces between them.

 

Vascular bundle– this makes up the vein in a leaf. It consists of xylem vessels and phloem tubes.

-Xylem vessels– these carry water around the plant

-Phloem tubes– carries food around the plant that has been made by the leaf