Leaves Leaves Horticulture 1Horticulture 1

What are the What are the functions of leaves?functions of leaves?

Capture lightCapture light Exchange gasesExchange gases Provide a site for photosynthesisProvide a site for photosynthesis Some leaves store food and waterSome leaves store food and water Some form new plants and provide Some form new plants and provide

supportsupport

Why does a plant Why does a plant need need

photosynthesis?photosynthesis? ““PHOTO” means lightPHOTO” means light ““SYNTHESIS” means to make or form something SYNTHESIS” means to make or form something

fromfrom

SO….Photosynthesis is a plant making something SO….Photosynthesis is a plant making something (food) from light.(food) from light.

Photosynthesis definition:Photosynthesis definition:

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

Why is photosynthesis Why is photosynthesis important?important?

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

Releases oxygenReleases oxygen

Recipe for PhotosynthesisRecipe for Photosynthesis

6CO2 + 12H2O 6CO2 + 12H2O sunlightsunlight > >

6O 2 + C6 H12O 6 + 6H2 O6O 2 + C6 H12O 6 + 6H2 O

Or in English=Or in English=

Carbon Dioxide + Water in Sunlight =>Carbon Dioxide + Water in Sunlight =>

Oxygen + Sugars/Food + WaterOxygen + Sugars/Food + Water

There are two parts of There are two parts of photosynthesis--the light and photosynthesis--the light and

dark reactions.dark reactions. The light reactions produce The light reactions produce

chemical energy from light.chemical energy from light. The dark reactions convert The dark reactions convert

carbon dioxide into carbon dioxide into carbohydrates.carbohydrates.

Leaves & gas exchangeLeaves & gas exchange Oxygen, Carbon Dioxide, Oxygen, Carbon Dioxide,

and Water exchanged from and Water exchanged from StomataStomata

Pores (stomata) open in day Pores (stomata) open in day to transpire H2O and allow to transpire H2O and allow gases to entergases to enter

Close during dry conditions Close during dry conditions to prevent H2O loss.to prevent H2O loss.

1. Leaves : External PartsA. 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. F. CutinCutin – fatty (waxy) substance in – fatty (waxy) substance in many plant cell walls & on outer many plant cell walls & on outer surface of epidermal cell wallssurface of epidermal cell walls - forming a - forming a CuticleCuticle – a protective – a protective covering on a green leaf that helps hold covering on a green leaf that helps hold in moisturein moisture(this gives the leaf a “glossy” (this gives the leaf a “glossy” appearance)appearance)

G. G. StipuleStipule – tiny leaf- – tiny leaf-like structures like structures at the base of a at the base of a

petiolepetiole

H. Axil – the angle H. Axil – the angle made by the petiole made by the petiole and the stem of the and the stem of the

plant.plant.

Leaves: Internal PartsA. 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 stomatesD. Chloroplasts- small green particles that contain chlorophyll, give leaves their green color and are necessary for photosynthesis