Leaf Structure and Function

Basic functions 1. Photosynthesis: process which plants use the energy from sunlight to produce sugar (for themselves) 2. Cellular Respiration

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)

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 contain chloroplasts, so they can manufacture food (for the plant) by photosynthesis Guard Cells are the only epidermal cells that can make sugar 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