Leaves Horticulture 1

What are the functions of leaves? Capture light Capture light Exchange gases Exchange gases Provide a site for photosynthesis Provide a site for photosynthesis Some leaves store food and water Some leaves store food and water Some form new plants and provide support Some form new plants and provide support

Why does a plant need photosynthesis? “PHOTO” means light “PHOTO” means light “SYNTHESIS” means to make or form something from “SYNTHESIS” means to make or form something from SO….Photosynthesis is a plant making something (food) from light. SO….Photosynthesis is a plant making something (food) from light.

Photosynthesis definition: a process by which plants combine water and carbon dioxide in the presence of chlorophyll and sunlight and produce carbohydrates and release oxygen. a process by which plants combine water and carbon dioxide in the presence of chlorophyll and sunlight and produce carbohydrates and release oxygen.

Why is photosynthesis important? Light is the most important source of energy for living things. Photosynthesis converts light into nutrients that can be used by plants and animals. Light is the most important source of energy for living things. Photosynthesis converts light into nutrients that can be used by plants and animals. Releases oxygen Releases oxygen

Recipe for Photosynthesis 6CO2 + 12H2O sunlight > 6CO2 + 12H2O sunlight > 6O 2 + C6 H12O 6 + 6H2 O Or in English= Carbon Dioxide + Water in Sunlight => Oxygen + Sugars/Food + Water

There are two parts of photosynthesis--the light and dark reactions. The light reactions produce chemical energy from light. The light reactions produce chemical energy from light. The dark reactions convert carbon dioxide into carbohydrates. The dark reactions convert carbon dioxide into carbohydrates.

Leaves & gas exchange Oxygen, Carbon Dioxide, and Water exchanged from Stomata Oxygen, Carbon Dioxide, and Water exchanged from Stomata Pores (stomata) open in day to transpire H2O and allow gases to enter Pores (stomata) open in day to transpire H2O and allow gases to enter Close during dry conditions to prevent H2O loss. Close during dry conditions to prevent H2O loss.

1. Leaves : External Parts A. Petiole- leaf stalk or part that connects leaf to stem. Petiole

B. Blade- the large, flat part of a leaf. C. Midrib- the large center vein. Midrib

D. Veins- the structural framework of leaf. Act like pipes to carry water & nutrients Veins

E. Margin- the edge of leaf. Margin (edge of the leaf)

F. Cutin – fatty (waxy) substance in many plant cell walls & on outer surface of epidermal cell walls - forming a Cuticle – a protective covering on a green leaf that helps hold in moisture - forming a Cuticle – a protective covering on a green leaf that helps hold in moisture (this gives the leaf a “glossy” appearance)

G. Stipule – tiny leaf-like structures at the base of a petiole H. Axil – the angle made by the petiole and the stem of the plant.

Leaves: Internal Parts A. Upper and lower epidermis- skin of the leaf that prevents the loss of too much moisture. B. Stomates- small openings under the leaf for breathing or transpiration (also called: stoma or stomata)

(Internal Parts-continued) C. Guard cells- open and close stomates D. Chloroplasts- small green particles that contain chlorophyll, give leaves their green color and are necessary for photosynthesis