Transcript CB098-008.31_Leaves - Workforce Solutions

The Form and
Structure of Leaves:
The Shoot System II
The Functions of Leaves
The leaf is organized to maximize sugar
production (photosynthesis) while minimizing
water loss (transpiration).
Main Leaf Functions
- Photosynthesis
- Transpiration (The main driving force for water transport up
the plant). Transpiration also cools the leaf.
- Modification (Modified leaves can provide water storage
and/or protection for the plant).
Leaves are initiated at the Shoot Apical Meristem
(SAM).
Typical dicot (a) and monocot (b) leaves compared.
Dicot leaves usually have netted venation and a
midrib; monocot leaves usually have parallel veins.
Leaf
Types
Red buckeye is
palmately compound,
black locust is
pinnately compound,
and honey locust is
double pinnately
(bipinnately)
compound.
Tissues of a Typical Leaf Blade
Tissues of a Typical Leaf Blade
This slide is used to describe the previous slide.
The Epidermis covers both sides of the leaf. It is covered by a waxy
cuticle made of cutin to minimize water loss. Guard cells (mostly
on the bottom side) control the opening of the stomates.
Palisade Mesophyll Cells (Parenchyma) are packed tightly to more
efficiently absorb sunlight. These cells are at right angles to the
epidermis and are often rectangular in shape.
Spongy Mesophyll Cells (Parenchyma) are loosely packed to allow
for more efficient gas exchange from their cells surfaces. These
cells are often more irregular in shape.
Vascular Bundles (Veins) are located in the mesophyll are made up
of xylem (water and nutrient-carrying) and phloem (sugarcarrying).
Bundle Sheath Cells are specialized mesophyll cells (parenchyma)
that surround the veins and separate them from the rest of the
mesophyll.
Lilac Leaf in Cross Section Showing the Midrib
Leaf Beginnings
Primodium – the
beginning or origin of
any part of an organ.
These figures represent the
develop of leaf primodia (plural
of primodium).
Remember that procambium
is a primary meristem and it
will give rise to primary
vascular tissues.
Leaf Form and Specialized Leaves
Leaf shape may depend on the plant’s age and the
environment.
Heterophylly – Different leaf shapes on a single plant.
Young bean
plants. The
plant on the left
is younger.
Effect of environmental conditions on the development
of buttercup leaves. Water Leaves (thin and deeply
lobed) versus Air Leaves (thicker and reduced lobes).
On a tree, certain
leaves receive more
sun (Sun Leaves)
and other receive
less sun (Shade
Leaves). Sun
leaves are thicker
and smaller. Shade
leaves are larger
and thinner (Larger
leaves have a
greater surface are
for receiving
sunlight).
Leaf Adaptations For Environmental Extremes
Xerophytes are plants that grow successfully in dry climates. They have
leaves designed to conserve water, store water and insulate against
heat. To inhibit water loss, some have sunken stomata, thick cuticles
and sometimes a multilayer of epidermis. Many fibers are in the leaves
of xerophytes that help to support the leaf and keep it form losing its
shape when it dries.
Jade (Crassula sp.)
in a fig plant.
is sunken in an Oleander Plant.
are tightly packed
to inhibit
evaporation in a
jade plant.
Hydrophytes grow in moist environments. They often grow wholly or
partly in submerged water. Their leaves are thin and they possess a
thin cuticle and the leaves are often deeply loped. Hydrophytes lack
characteristics to conserve water.
Mesophytes grow in moderate environments (moderate moisture and
temperature). They often have typical dicot leaves.
Leaf Modifications For Special Functions
Spine – sharp pointed modified leaves that help plants
deter predators. Example: Cacti with spines.
Stipule – a leaf-like structure from
either side of the leaf base.
Stipules are leafy appendages
usually in pairs at the base of the
petiole. These are NOT always
present.
Black Locust
Tendril – Can either be a leaf or stem.
Tendrils are slender coiled organs that
aid in the support of stems. In some
plants, the entire leaf becomes a tendril.
Example shown: Trumpet Creeper
climbing another plant using tendrils.
Bulbs are modified stems but
with fleshy leaves present.
Leaf Abscission is the Seasonal Removal of Leaves
Abscission – the process of leaves separating from a stem.
Abscission Zone – zone of delicate, thin-walled cells extending across the
base of the petiole, the breakdown disjoins the leaf (or fruit) from the stem.
In the abscission zone, parenchyma cells are smaller, vascular tissue is
shorter and fibers are absent. Leaf abscission in induced by hormonal
changes caused by cold or short days. Before abscission, leaves move much
of their nutrients to the stem.
BIO 141 Botany with Laboratory
•
This product is sponsored by a grant awarded under the President’s Community-Based Job Training Grants as implemented by the U.S. Department of
Labor’s Employment and Training Administration. The information contained in this product was created by a grantee organization and does not
necessarily reflect the official position of the U.S. Department of Labor. All references to non-governmental companies or organizations, their services,
products, or resources are offered for informational purposes and should not be construed as an endorsement by the Department of Labor. This product
is copyrighted by the institution that created it and is intended for individual organizational, non-commercial use only.