Vascular Plants with Seeds
C9L3P5
Leaves
External Structures of Leaves
Margin
Blade: the flat portion
of a leaf
Petiole: the stalk of a
leaf; attaches leaf to stem
Margin: the edge of a
leaf’s blade
Veins: the pipelines that
carry food & water
Node: place on stem
where leaves are attached
External Structures of Leaves
Stipule: a small leaf like or scale like structure
on a plant that helps to cover a leaf while it is
developing
Leaf Venation
Two basic patterns of leaf venation:
• Parallel Venation
• Netted Venation
Parallel Venation
A series of veins which
originate at the stem and
proceeds to the tip of the
leaf
Occurs in monocots – corn,
grass, irises, orchids
Netted Venation
Palmate: two or more main veins
coming from a single point
Examples: maple, ivy, geraniums
Pinnate: if the veins branch off one
large central vein called a midrib
Examples: oaks, apple trees,
African violets
Classification of Leaves


Simple leaves
Compound leaves
Simple or Compound?
Simple Leaves: one blade on each petiole
Simple or Compound?
Compound: more than one blade on each petiole
Each small blade on a compound leaf is
referred to as a leaflet
Sessile Leaves
Sessile leaves lack petioles
Sessile Leaves
Grasses and certain other monocots have
sessile leaves that attach to the stem by way of
a sheath that seems to wrap around the stem
Leaf Mosaic
Alternate
Opposite
Whored
Leaf mosaic: the arrangement
of leaves on a stem
Leaf Mosaic
Alternate Mosaic: leaves alternate from
opposite sides of the stem (one petiole per
node)
Leaf Mosaic
Opposite Mosaic: two leaves grow from the
same point on the stem (two petioles per
node)
Leaf Mosaic
Whorled Mosaic: three or more leaves
grow from a single point on a stem (3 or
more petioles per node)
Leaf Mosaic
Leaf Shapes
Linear
Lobed
Circular
Cordate
Deltoid
Linear Leaf Shape
long and narrow
Lobed
Leaf Shape
Cordate Leaf Shape
kidney or heart-shaped
Deltoid Leaf Shape
deltoid-shaped
Circular Leaf Shape
Leaf Margins
Entire
Serrate
Undulate
Dentate
Entire Leaf Margin
smooth margin with no teeth
Serrate Leaf Margin
toothed margins
Undulate Leaf Margin
wavy margins
Dentate Leaf Margin
teeth point out
The internal structures of leaves.
Leaves

Most leaves are the major site of
photosynthesis for the plant.

The top and bottom layers of a leaf are made
of epidermal tissue.
The Covering of a Leaf
The Epidermis
The Epidermis
• the top and bottom layer
• one cell layer in thickness
• lacks chlorophyll
• serves as protection
• often secrets a waxy substance that
forms a cuticle
• usually transparent
The Cuticle
Cuticle
Epidermis
waxy
substance
made by some
epidermal
cells for
protection
The Lower Epidermis
• tiny openings called stomata
(stoma, sing.)(or leaf pores) permit
the exchange of gases between
atmosphere and spaces in leaf
• main purpose - to allow air to move
in and out of the leaves
Dr. Gerald Van Dyke/Visuals Unlimited/Getty Images
Most leaves have a small
opening in the epidermis
called stomata.
Stomata
Dr. Gerald Van Dyke/Visuals Unlimited/Getty Images
When the stomata open, carbon dioxide,
oxygen, and water vapor can pass through
them.
The Lower Epidermis
• may be very abundant (apple tree
leaf - 47,000 stomata per square inch;
oak tree –
100,000)
• guard cells - two crescent-shaped
cells around each stomata; open and
close the stomata
The Lower Epidermis
Stoma
Guard
Cells
The Lower Epidermis
Stomata & Guard Cells
Guard Cells
Stomata
The Lower Epidermis
Stomata & Guard Cells
The Lower Epidermis
Guard Cells
Guard Cells
Stomata & Guard Cells
Internal Leaf Structures
Between the upper and lower epidermis is the
mesophyll.
It is in the mesophyll where most of the
photosynthesis takes place.
It is structural tissue called parenchyma.
Mesophyll is divided into two layers:
Palisade Mesophyll
Spongy Mesophyll
Internal Leaf Structures
Palisade Mesophyll
Below the upper epidermis are rows of tightly
packed cells called palisade mesophyll cells
where photosynthesis mainly occurs.
Palisade Mesophyll
• located toward the upper side of the
leaf
• consists of elongated, column like cells
• there may be several layers
• abundance of chloroplasts move in a
circle
Spongy Mesophyll
• located toward the lower side of the leaf
• sometimes sandwiched in the middle
• consists of large, irregularly shaped cells
• separated by large air spaces
• form a system of passages throughout the
leaf that permits air to come in contact with
the individual cells
Veins
(Fibrovascular Bundles)
• run through the
mesophyll
• contain the vascular
tissue xylem and phloem
• contain thick-walled
strengthening collenchyma
tissue
Scanning Electron Microscopic Picture of a
Freeze-Dried Cross-Section Through a Bean Leaf
E: Upper and lower
epidermis,
Sz: Guard cell,
P: Cells of the
palisade
parenchyma,
S: Cells of the
spongy
parenchyma,
I: Intercellular
space.
Cross Section of a Leaf
Cross Section of a Leaf
Cross Section of a Leaf
Cross Section of a Leaf
Cross Section of a Leaf
Cross Section of a Leaf
Cross Section of a Leaf
GAS EXCHANGE IN PLANTS
(1) The cycle of oxygen and carbon dioxide –
takes place in green parts of plants
O2 from photosynthesis
CO2 from cellular respiration
(2) stomata – takes place in leaves
GAS EXCHANGE IN PLANTS
(3) lenticels – takes
place in the woody
parts of plants
lenticels:
small openings in the
woody parts of plants
GAS EXCHANGE IN PLANTS
(4) epidermis – takes place in
underground parts; gases exchanged
through the thin coverings; helped by
burrowing of worms,
insects, and other
organisms (helps
bring air; helps soil
to drain)
GAS EXCHANGE IN PLANTS
Plants with roots
always in H2O and
sometimes leaves special networks of
air tubes in
fibrovascular
bundles
What Plants Do With Glucose
(the sugar they make)?
glucose - contains in a stored form the
energy captured from the sun
Cells that carry on photosynthesis
make more sugar than they need and
they pass glucose along to other plant
parts through the phloem.
What Plants Do With Glucose
(the sugar they make)?
Some glucose molecules are not used for
energy but are hooked together to make
cellulose.
Some glucose molecules are stored
as starch (potatoes, wheat, bananas,
corn) and some convert the glucose to
lipids (corn oil, peanut oil, olive oil).
Leaves