#46 Leaf structure

The leaf consist of a broad, flat part called the lamina, which is joined to the rest of the plant by a leaf stalk or petiole. Running through the petiole are vascular bundles, which then form the veins in the leaf.

Although a leaf looks thin, its is made up of several layers of cells. You can see these if you look at a transverse section (cross-section) of a leaf under a microscope.

1. Cuticle:

made of wax – waterproofing the leaf
secreted by cells of the upper epidermis

2. Upper epidermis

thin and transparent – allows light to pass through
no chloroplasts are present
act as a barrier to disease organisms

3. Palisade mesophyll

main region for photosynthesis
cells are columnar (quite long) and packed with chloroplasts to trap light energy
receive CO₂ by diffusion from air spaces in the spongy mesophyll

4. Spongy mesophyll

cells are more spherical and loosely packed
contain chloroplasts, but not as many as in palisade cells
air spaces between cells allow gaseous exchange – co₂ to the cells, o₂ from the cells during photosynthesis

5. Vascular bundle

this is a leaf vein, made up of xylem and phloem
xylem vessels bring water and minerals to the leaf
phloem vessels transport sugars and amino acids away (translocation)

Photo credit: Pass My Exams

6.Lower epidermis

acts as a protective layer
stomata are present to regulate the loss of water vapour (transpiration)
site of gaseous exchange into and out of the leaf

7. Stomata