Leaves

LeavesAbove ground plant

organ used to capture sunlight for photosynthesis

Typically flat and thin to allow light to penetrate fully into the tissues

Leaf FunctionsLeaves perform the

following functions for the plant:

1)Photosynthesis

2)Storage of starch

3)Contain the majority of

sites for gas exchange (stomata)

Leaf MorphologyLeaf morphology is

important for plant identification.

Nodes are the place where leaves attach to the branch.

Leaves can be arranged oppositely (paired from a node), whorled (more than 2 leaves from one node) or alternately (one leaf per node) on a branch.

Leaf MorphologyLeaves can be

simple or compound.

Compound leaves can be palmate (having leaflets arranged like fingers in a hand) or pinnate (having leaflets arranged along the main vein).

Leaf MorphologyBlade: the actual

‘leaf’, also called the lamina

Petiole: the attachment leading from the node to the blade

Midrib: the central vein (vascular path) of the blade

Leaf MorphologyMargin: the edge of the leaf. The margin can be a

key characteristic that helps identify the plant

Leaf Cross-SectionA leaf is considered to

have 3 distinct sections:

1)An epidermis that covers both the top and bottom of the leaf

2)A mesophyll layer on the inside that does the majority of the photosynthesis

3)Vascular bundles to transport water and sugar to and from the leaf

Leaf Cross-Section

The epidermis is covered with a waxy cuticle to help prevent against water loss.

The epidermis has tiny pores called stomata with guard cells on either side. They work together to exchange gases and water vapour between the outside environment and the inside of the leaf.

Stomata are more common on the underside of the leaf.

Leaf Cross-SectionThe mesophyll layer

contains upright palisade cells that contain many more chloroplasts than the spongy layer below them.

Palisade layer is used for photosynthesis and the spongy layer is more spacious to allow for maximum absorption of carbon dioxide for photosynthesis.

PhotosynthesisPhotosynthesis is the

conversion of light energy, water and carbon dioxide into sugar and oxygen.

The light energy comes from the Sun and is used by chloroplasts in the leaves of the plant.

The water comes from the soil through the roots.

PhotosynthesisThe carbon dioxide

enters the leaf through the stomata

Oxygen will leave the stomata as a waste product

The other end product, sugar, is moved to different areas of the plant depending on need… this will be in an upcoming lecture…