Leaf Structure and Function

Basic functions

• 1. Photosynthesis: process which plants use the energy from sunlight to produce sugar (for themselves)

• 2. Cellular Respiration: the process whereby cells use sugar to release stored energy

Photosynthesis

• The conversion of carbon dioxide using sunlight energy and water into sugars and oxygen

• is associated with the actions of the green pigment chlorophyll

Leaf Structure

• leaf is a plant organ and is made up of a collection of tissues

• Like a sandwich!• 1. The epidermis that covers the upper and

lower parts • 2. The mesophyll inside the leaf that is rich in

chloroplasts (light absorbers during photosynthesis)

• 3. The arrangement of veins (the vascular tissue)

Components of a Leaf

Think about your sandwich you had for lunch!

1a. Upper Epidermis

• The epidermis is the outer layer of cells covering the leaf

• forms the boundary separating the plant's inner cells from the external world

• Has a waxy texture• Functions: protection against water loss by way

of transpiration, regulation of gas exchange, secretion of metabolic compounds, and (in some species) absorption of water

2. Mesophyll

• Most of the inside of the leaf between the upper and lower layers of epidermis

• Primary location of photosynthesis in the plant

• Composed of 2 layers

Layers

• A) Palisade Layer: tightly packed cells that contain choroplasts (convert light energy in photosynthesis)

• B) Spongy Layer: cells contain many spaces between them for gas exchange and carbon dioxide absorption, contain the plants veins

1b: Lower Epidermis

• Contains pores called stomata which are surrounded by chloroplast-containing guard cells

• stomata regulate the exchange of gases and water vapor between the outside air and the interior of the leaf

• stomata are more numerous in the lower epidermis of the leaf than the upper epidermis

Guard Cells

• Guard cells contain chloroplasts, so they can manufacture food (for the plant) by photosynthesis

• At night, the sugar is used up and water leaves the guard cells, so they become flaccid and the stomata pore closes, this reduces the amount of water vapour escaping from the leaf

3. Veins

• Are the vascular tissue of the leaf • located in the spongy layer of the

mesophyll• veins are made of: 2 components• 1. Xylem: tubes that bring water

and minerals from the roots into the leaf.

• 2. Phloem: tubes that usually move sap, with dissolved sucrose, (produced by photosynthesis) out of the leaf

Where would each term go?

Upper Epidermis

Lower Epidermis

Veins

Mesophyll