The Leaf
• The Leaf is the Main photosynthetic organ
in a plant.
• Controls gas exchange in plants.
• Controls the amount of water loss in plants
when it is hot and dry by:
– closing their stomates.
– produce a thick cuticle layer.
– reduce the surface area of their leaves.
Fig 30.10
Leaf Cross Section
Waxy Cuticle & Upper Epidermis
Waxy cuticle
Upper Epidermis
•The waxy cuticle is a thin layer atop the
epidermis.
•Its function is to reduce/prevent
water loss from the leaf.
•In arid conditions (desert) this cuticle
layer can be quite thick.
•Upper Epidermis cells contain no
chloroplasts – not true of the stoma
cells.
•They form layers on the upper and
lower surfaces of the leaf.
•Their function is to prevent water
getting out and stopping unwanted
substances/organisms getting in.
Palisade Mesophyll Layer
Palisade mesophyll layer
•The palisade mesophyll layer is where most
of the photosynthesis occurs in the leaf.
•The palisade cells contain a lot of
chloroplasts to help them perform this
photosynthesis.
•The cells of this layer are closely packed
together to maximize the absorption of light.
•In the leaf cross-section we can see the
palisade cells are only found in the upper
part of the leaf.
Spongy Mesophyll Layer
•The cells in the spongy mesophyll layer are
not as closely packed as the cells in the
palisade mesophyll layer.
•This creates air spaces inside the leaf to
enable gases to move in and out. Bringing in
CO2 and releasing 02 and Water Vapor
•There are not as many chloroplasts in the
spongy mesophyll cells as there are in the
palisade mesophyll cells – but
photosynthesis still occurs in the spongy
mesophyll layer.
Spongy mesophyll layer
Air space
Lower Epidermis and Stomata
Stomata
Guard Cell
•Lower epidermis is the bottom layer of the leaf,
and is one cell thick
•May or may not contain a cuticle
•Within the Lower Epidermis, there are some
holes found in leaves called stoma.
•These holes allows gases to diffuse in and
out of the leaves.
•The stoma are formed by two highly
specialized epidermis cells, called guard
cells.
•Guard cells are the only epidermis cells
that contain chloroplasts.
•The stoma open and close (using turgor
pressure) depending upon the requirements of
the plant.
•It is through these stoma that water leaves the
leaf, the process that powers transpiration.
Transpiration
• Process by which
evaporation of water
from leaf surface draws
water from roots
upward
Stomata and Guard Cells
Vein- Leaf Transport
• The veins provide the
transport of materials in the
leaf
– Carries water, minerals, and
food through the leaf and rest
of the plant
• Has two parts
– Xylem- water and mineral
transport
– Phloem- sugar and food
transport
Xylem and Phloem
Exercise 4: Leaf Structure
1. ___________
Waxy cuticle
2. ___________
Epidermis
3. ______________________
Palisade mesophyll layer
4. __________
Air space
5. _____________________
Spongy mesophyll layer
6. ________
Stomata
7. __________
Epidermis