Download The Leaf

The Leaf
 Introduction
 Leaf Arrangements and Types
 Internal Structure of Leaves
 Stomata
 Mesophyll and Veins
 Specialized Leaves
 Autumnal Changes in Leaf Color
 Human and Ecological Relevance of Leaves
Function:
 Photosynthesis (food production for the whole plant).
 Transpiration
Structure
 Blade: Flat expanded area or lamina
 Petiole: stalk that connects leaf blade to stem, and transports
materials.
 Veins: Vascular Bundles
 Stipules at base of petiole
Leaves of flowering plants associated with leaf gaps and have axillary
Leaves may be simple or
compound.
Simple leaves
 Simple leaves: With a single
blade
 Compound leaves: Blade
divided into leaflets
 Pinnately compound leaves -
Leaflets in pairs along rachis
(petiole)
 Bipinnately compound leaf -
Bipinnately
compound leaf
Leaflets subdivided
 Palmately compound leaves - All
leaflets attached at same point at
end of petiole.
Palmately
compound leaf
Simple Leaf
Compound
Leaf
 Leaves are attached to stems at nodes, with stem
regions between known as internodes.
 Phyllotaxy - Arrangement of leaves on stem
Alternate - One leaf per node
Opposite - Two leaves per node
Whorled - Three of more leaves at a node
Alternate
Opposite
Whorled
The Leaf Arrangement
 Monocots - Primary veins parallel = Parallel venation
 Dicots - Primary veins divergent in various ways =
netted or reticulate venation.
 Dichotomous venation - Veins fork evenly and
progressively from base of blade.
Parallel
venation
Reticulate venation
Dichotomous
venation
 Venation - Arrangement of veins in a leaf or leaflet
blade
 Pinnately veined leaves - Main midvein included
within enlarged midrib.
 Secondary veins branch from midvein.
 Palmately veined leaves - Several primary veins
fan out from base of blade.
Pinnate
venation
Palmate
venation
Three regions: Epidermis, mesophyll, veins
(vascular bundles)
Epidermis: Single layer of cells covering the entire
surface of the leaf
 Devoid of chloroplasts
 Coated with cuticle (with cutin)
 Functions to protect tissues inside leaves
 Waste materials may accumulate in epidermal
cells.
 Different types of glands may also be present in
the epidermis.
Lower epidermis typically has a thinner layer of cutin and is
perforated by numerous stomata.
The stomata bordered by two guard cells.
 The guard cells originate from the same parent cell
(they are sister cells), and contain chloroplasts.
 Their primary functions are:
• Regulate gas exchange between leaf interior and
atmosphere
• Regulate evaporation of water
• Changes in amount of water in guard cells cause them
to inflate or deflate.
• Inflate - Stomata open
• Deflate - Stomata close
 Most photosynthesis takes
place in the mesophyll
between the two epidermal
layers. The mesophyll is
comprised of the
 Palisade Mesophyll:
Compactly stacked, barrelshaped parenchyma cells,
commonly in two rows and
contains most of leaf’s
chloroplasts.
 Spongy Mesophyll
Loosely arranged
parenchyma cells with
abundant air spaces
 Veins (vascular bundles) are scattered throughout
mesophyll. They consist of xylem and phloem tissues
surrounded by bundle sheath of thicker-walled
parenchyma
Review: Sketch of a cross section of a dicot leaf
Typical Dicot
Leaf
 Monocots have some differences: Usually do not have
mesophyll differentiated into palisade and spongy layers
Often have bulliform
cells on either side of
main central vein:
Bulliform cells partly
collapse under dry
conditions and they
cause the leaf to fold or
roll, reducing
transpiration
Monocot leaf cross section
SPECIALIZED LEAVES
Shade Leaves
 Receive less total light than sun leaves.
 Compared to sun leaves, shade leaves:
 Tend to be larger.
 Tend to be thinner.
 Have fewer well
defined mesophyll
layers and fewer
chloroplasts.
 Have fewer hairs
 Leaves of Arid Regions
 Arid regions have limited availability of water, wide temperature
ranges, and high light intensities.
 Leaves reduce loss of water by:
 Thick, leathery leaves
 Fewer stomata or sunken stomata
 Succulent, water-retaining leaves, or no leaves
 Dense, hairy coverings
 Leaves of Aquatic Areas
 Less xylem and phloem
 Mesophyll not differentiated into palisade and spongy layers.
 Large air spaces
Water lily leaf with highly
developed spongy parenchyma
Dune grass leaf with
highly developed
sclerenchyma
 Tendrils
Modified leaves that curl around more rigid
objects, helping the plant to climb or to support
weak stems. For example Garden peas
–
Cacti
o Leaf tissue replaced with
sclerenchyma.
o Photosynthesis occurs in stems.
Tendrils
SPECIALIZED LEAVES
 Thorns: Modified stems
arising in the axils of leaves of
woody plants
Thorn

Prickles: Outgrowths from
epidermis or cortex
Modified leaves
The leaves have been completely
modified into a cactuses thorns.
Storage leaves
Succulent leaves are
modified for water storage.
These leaves have
parenchyma cells with large
vacuoles. Like in Aloe.
Found in many desert
plants and in some cases,
the fleshy leaves also store
carbohydrates like in
onions.
Window leaves
Found in succulent desert plants of Africa.
In this case the leaves are buried in the ground, except for
the exposed ends. The ends have a transparent, thick
epidermis and transparent water storage cells underneath.
These “windows” allow light into leaf, while buried leaves
keep plant from drying out
 Floral Leaves (bracts)
 At bases of flowers or flower stalks
 Poinsettia - Flowers do not have petals, instead brightly
colored bracts surround flowers.
 Clary’s sage - Colorful bracts are at top of flowering
stalks above flowers.
Poinsettia
Clary’s sage
 Reproductive Leaves
 New plants at leaf tips. Known as the “walking fern”.
This is not a fern, but the succulent known as
Kalanchoe (crassulaceae family).
 Air plant - Tiny plantlets along leaf margins
Air Plant
SPECIALIZED LEAVES
Insect-Trapping Leaves
Pitcher Plants:
 Grow in swampy areas and
bogs where nitrogen and other
elements are deficient in the
soil.
 The have specialized leaves
trap and digest insects. The
insects trapped and digested
inside cone-shaped leaves,
hence the name “pitcher
plant”.
Pitcher plant
SPECIALIZED LEAVES
Insect-Trapping Leaves
Sundews
 Have round to oval leaves
covered with glandular hairs
that have a sticky fluid of
digestive enzymes at tip
Venus’s Flytraps
 Only in North Carolina and
South Carolina
 Blade halves trap insects.
Insect-Trapping Leaves
Bladderworts
 Submerged or floating in shallow water
 Tiny bladders on leaves have trap doors that trap
insects inside bladders.
Bladder of bladderwort
Flower-Pot Leaves
 Leaves develop into urnlike pouches that
become home of ant
colonies.
 Ants carry in soil and
add nitrogenous wastes
that provide good
growing medium for the
plant’s own roots. An
example is Dischidia, an
epiphyte of Australia
Flower-pot leaf sliced lengthwise
Chloroplasts of mature leaves contain several
groups of pigments:
 Chlorophylls - Green
 Carotenoids – Oranges and Yellows
 Xanthophylls: Yellows
In fall, chlorophylls break down and other colors are
revealed.
Water soluble anthocyanins (red or blue) and
betacyanins (red) may also be present in the
vacuole.
Maple leaves
American Beech
leaves
Sassafras
leaves
Northern Red oak
Pignut hickory
White Oak
Flowering Dogwood
PHOTOSYNTHESIS
1. Definition
PHOTO = produced by light
SYNTHESIS = manufacturing.
PHOTOSYNTHESIS is the process whereby plants,
algae and some bacteria, use the energy of the
sun to synthesize organic compounds (sugars)
from inorganic compounds (CO2 and water).
Carbon Dioxide + Water+ Light
CO2 + H2O+Light
Glucose + O2
C6H12O6 + O2 + H2O
3. Where?
 Chlorophyll a is the primary photosynthetic pigment that
drives photosynthesis.
 Other pigments such as chlorophyll b, carotenes and
xanthophyll can be present. These are known as
accessory pigments or antenna pigment.
 They absorb light at different wavelengths, extending
the range of light useful for photosynthesis.
 Accessory pigments can collect light but the only pigment
that can transform sunlight (light energy) into the
chemical bonds of Glucose (chemical energy) is
chlorophyll a.
PHOTOSYNTHESIS is one of the most important
biological process on earth!
 Provides the oxygen we breathe
 Consumes much of the CO2
 Food
 Energy
 Fibers and materials
 Landscaping - Shade trees
 Food - Cabbage, lettuce, celery petioles, spices
 Dyes
 Perfumes - Oils of orange tree, lavender
 Ropes and Twine - Agave, hemp fibers
 Drugs - Narcotics, tobacco, marijuana
 Beverages - Tea, tequila (agave leaves)
 Insecticides - Rotenone
 Waxes - Carnauba and caussu waxes
 Aesthetics - Floral arrangements, gardens
 Introduction
 Leaf Arrangements and Types
 Internal Structure of Leaves
 Stomata
 Mesophyll and Veins
 Specialized Leaves
 Autumnal Changes in Leaf Color
 Human and Ecological Relevance of Leaves