Leaves Horticulture 1

Horticulture 1
What are the
functions of leaves?
Capture light
Exchange gases
Provide a site for photosynthesis
Some leaves store food and water
Some form new plants and provide
Why does a plant
“PHOTO” means light
“SYNTHESIS” means to make or form something
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.
Why is photosynthesis
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
Recipe for Photosynthesis
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 dark reactions convert
carbon dioxide into
Leaves & gas exchange
Oxygen, Carbon Dioxide,
and Water exchanged from
 Pores (stomata) open in day
to transpire H2O and allow
gases to enter
 Close during dry conditions
to prevent H2O loss.
1. Leaves : External Parts
A. Petiole- leaf stalk or part
that connects leaf to stem.
B. Blade- the large, flat part
of a leaf.
C. Midrib- the large center vein.
D. Veins- the structural
framework of leaf. Act like
pipes to carry water &
E. Margin- the edge of
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
(this gives the leaf a “glossy”
G. Stipule – tiny leaf-like
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 epidermisskin 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