Plant cell types
rise by mitosis
from a meristem.
A meristem may
be defined as a
region of localized
mitosis.
X section of a leaf
Key Words
Waxy cuticle
Waterproof layer atop the epidermis
Stoma
Pores that allow gaseous exchange
Air spaces
Found in the spongy mesophyll layer,
enable gases to reach the leaf cells
Epidermis
One-cell thick outer layer of cells that
prevent water loss from the leaf
Palisade
mesophyll cell
Contain numerous chloroplasts and are
densely packed
Spongy
mesophyll cell
Loosely packed cells that do not contain
as many chloroplasts as palisade cells
Waxy Cuticle & Epidermis
Waxy cuticle
Epidermis
The waxy cuticle is a thin layer
atop the epidermis.
Its function is to reduce the water
lost from the leaf.
In arid conditions this cuticle layer
can be quite thick.
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.
Stomata
There are 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.
These cells, called guard cells, are
the only epidermis cells that contain
chloroplasts.
The stoma open and close
depending upon the requirements of
the plant.
It is through these stoma that water
leaves the leaf, the process that
powers transpiration.
Stomata
Palisade Mesophyll Layer
The palisade mesophyll layer is
where most of the photosynthesis
occurs in the leaf.
Palisade mesophyll layer
The palisade cells contain a lot of
chloroplasts to help them perform
this photosynthesis.
The palisade cells are closely
packed together to maximize light
absorption.
In the leaf cross-section we can see
the palisade cells are only found in
the upper part of the leaf.
• Cells of the mesophyll make up the bulk of
internal leaf tissue and are the major site of
photosynthesis in a plant by virtue of
containing large populations of chloroplast
organelles. The differentiation of the
mesophyll and its coordinated expansion is
important to leaf function because light
interception by chloroplasts and gas exchange
in the internal airspaces of the leaf are crucial
to optimize rates of photosynthesis.
A Thylakoid is a membrane-bound
compartment inside chloroplasts and
cyanobacteria. They are the site of the lightdependent reactions of photosynthesis. The
word "thylakoid" is derived from the Greek
thylakos, meaning "sac". Thylakoids consists
of a thylakoid membrane surrounding a
thylakoid lumen. Chloroplast thylakoids
frequently form stacks of disks referred to as
"grana" (singular: granum). "Grana" is Latin
for "stacks of coins". Grana are connected by
intergrana or stroma thylakoids, which join
granum stacks together as a single functional
compartment.
1. outer membrane
2. intermembrane space
3. inner membrane (1+2+3: envelope)
4. stroma (aqueous fluid)
5. thylakoid lumen (inside of thylakoid)
6. thylakoid membrane
7. granum (stack of thylakoids)
8. thylakoid (lamella)
9. starch
10. ribosome
11. plastidial DNA
12. plastoglobule (drop of lipids)
Photosynthesis
Chloroplasts are organelles of plant cells that contain a green
substance called chlorophyll.
Scientists believe chlorophyll absorbs light energy and this
energy is then used to make food.
The raw materials of photosynthesis are carbon dioxide and
water. The waste product of this reaction is oxygen.
The carbon dioxide required is absorbed through the stoma in
the leaves – this is how the oxygen is also removed.
The water required is absorbed by the roots.
The word equation for this reaction is...
The chemical equation for this reaction is...
6H2O + 6CO2  C6H12O6 + 6O2
The thylakoid membrane is
the site of the lightdependent reactions of
photosynthesis with the
photosynthetic pigments
embedded directly in the
membrane.
The thylakoids are the site of the lightdependent reactions of photosynthesis.
These include light-driven water
oxidation and oxygen evolution, the
pumping of protons across the thylakoid
membranes coupled with the electron
transport chain of the photosystems and
cytochrome b6f complex, and ATP
synthesis by the ATP synthase utilizing
the generated proton gradient.
Chlorophyll molecule