Leaf Structure

Functions of Leaves Main photosynthetic organ Broad, flat surface increases surface area for light absorption Have systems to prevent water loss Stomata open in day but close at night or when hot to conserve water waxy cuticle on surface System of gas exchange Allow CO2 in and O2 out of leaf Elephant Ear Plant

Structure of a leaf Waxy cuticle – waterproof layer (reduces water loss from surface) Veins (stands of xylem and phloem from midrib) Form a bundle of vascular tissue xylem Stomata – pores on underside of leaf through which carbon dioxide and water vapour are exchanged phloem Midrib (vascular tissue i.e. phloem and xylem) Leaf stalk (petiole) Stem (supports plant)

Section through a leaf Upper side of leaf lower side of leaf waxy cuticle to prevent water loss Upper side of leaf lower side of leaf Upper epidermis – transparent, no chloroplasts nucleus Palisade cell – many chloroplasts vacuole cytoplasm Chloroplast – membranes covered with chlorophyll Spongy mesophyll cells – fewer chloroplasts xylem – transports water phloem – transports food (translocation) Air space lower epidermis Stoma Guard cells

Outer layer- upper surface 1.waxy 2. Epidermis transparent so no chlorophyll 1. The waxy cuticle is a waterproof layer which cuts down water loss by evaporation. 2. The upper cells of the leaf make up the epidermis. They are transparent so light passes straight through them into the next layer of cells…

Outer layer- bottom surface Leaf epidermis with stomata- scanning electron microscope State that plants take in carbon dioxide from the air through stomata which can open and close Interpretation- stomata are tiny pores on the surface of a leaf. Carbon dioxide enters the leaf through stomata. During the day stomata are open. During the night stomata are closed. Know that water vapour is lost through stomata On the lower surface of the leaf there are tiny pores called stomata (singular- stoma) which open and close. Stomata let CO2 diffuse in. Water vapour and oxygen (O2) move out.

Guard Cells Stoma

Function of Stomata What process involves using CO2 and H2O releasing O2 as a waste product? Photosynthesis If the plant needs water for photosynthesis, why is water coming out of the stoma? Guard Cells Guard Cells What goes out? O2 H2O CO2 What goes in? Stoma Open Stoma Closed Stoma

Function of Guard Cells These stomata (leaf openings) naturally allow water to evaporate out. Why would the plant close stomata with guard cells? Prevent excess water loss (conserve water) So what is the point of having stomata? Allow gas exchange for photosynthesis Guard Cells Guard Cells Stoma Open Stoma Closed Guard cells open by inflating with extra water. They do this by pumping K+ ions into the cell, which causes water to rush in via osmosis to diffuse the high ion concentration.

Stomata- open Stomata have guard cells surrounding them to control their opening & closing. When there is plenty of water (daytime) the water enters the guard cells and becomes turgid and curved. This opens the stomata and water can escape.

Stomata- closed When there is little water the guard cells loose water and become flaccid = less curved. This closes the stomata and keeps water in the leaf. This happens at night. G