Plant leaves help to sustain life on earth as they generate food for both plant and animal life. The leaf is the site of photosynthesis in plants. Photosynthesis is the process of absorbing energy from sunlight and using it to produce food in the form of sugars. Leaves make it possible for plants to fulfill their role as primary producers in food chains. Not only do leaves make food, but they also generate oxygen during photosynthesis and are major contributors to the cycle of carbon and oxygen in the environment. Leaves are a part of the plant shoot system, which also includes stems and flowers. 1. Plant leaves are very important structures as they help to maintain life on earth by generating food (sugars) via photosynthesis. 2. Leaves can have different shapes and sizes. The basic components of leaves in flowering plants (angiosperms) include the blade, the petiole, and the stipules. 3. There are three main tissues found in leaves: the epidermis, the mesophyll, as well as vascular tissue. Each tissue type is composed of layers of cells. In addition to performing photosynthesis, some plants have other highly specialized functions. Examples include carnivorous plants that can 'eat' insects. 4. Some animals, like the Indian leafwing butterfly, mimic leaves to camouflage themselves from predators.

1. Plant Leaf
Dr. Naveen Gaurav
Associate Professor and Head
Department of Biotechnology
Shri Guru Ram Rai University
Dehradun

2. Plant leaves: Plant leaves help to sustain life on earth as they generate food for both
plant and animal life. The leaf is the site of photosynthesis in plants. Photosynthesis is the
process of absorbing energy from sunlight and using it to produce food in the form
of sugars. Leaves make it possible for plants to fulfill their role as primary producers in food
chains. Not only do leaves make food, but they also generate oxygen during photosynthesis
and are major contributors to the cycle of carbon and oxygen in the environment. Leaves
are a part of the plant shoot system, which also includes stems and flowers.
1. Plant leaves are very important structures as they help to maintain life on earth by
generating food (sugars) via photosynthesis.
2. Leaves can have different shapes and sizes. The basic components of leaves in flowering
plants (angiosperms) include the blade, the petiole, and the stipules.
3. There are three main tissues found in leaves: the epidermis, the mesophyll, as well as
vascular tissue. Each tissue type is composed of layers of cells.
In addition to performing photosynthesis, some plants have other highly specialized
functions. Examples include carnivorous plants that can 'eat' insects.
4. Some animals, like the Indian leafwing butterfly, mimic leaves to camouflage themselves
from predators.
Leaf Anatomy: Leaves can be found in a variety of shapes and sizes. Most leaves
are broad, flat and typically green in color. Some plants, such as conifers, have
leaves that are shaped like needles or scales. Leaf shape is adapted to best suit the
plant's habitat and maximize photosynthesis. Basic leaf features
in angiosperms (flowering plants) include the leaf blade, petiole, and stipules.

4. Blade - broad portion of a leaf.
Apex - leaf tip.
Margin - leaf edge boundary area. Margins can be smooth, jagged (toothed), lobed, or
parted.
Veins - vascular tissue bundles that support the leaf and transport nutrients.
Midrib - central main vein arising from secondary veins.
Base - area of the leaf that connects the blade to the petiole.
Petiole - thin stalk that attaches the leaf to a stem.
Stipules - leaf-like structures at the leaf base.
Leaf shape, margin, and venation (vein formation) are the main features used in plant
identification.
Leaf Tissues:

5. Leaf tissues are composed of layers of plant cells. Different plant cell types form three main
tissues found in leaves. These tissues include a mesophyll tissue layer that is sandwiched
between two layers of epidermis. Leaf vascular tissue is located within the mesophyll layer.
Epidermis
The outer leaf layer is known as the epidermis. The epidermis secretes a waxy coating called
the cuticle that helps the plant retain water. The epidermis in plant leaves also contains
special cells called guard cells that regulate gas exchange between the plant and the
environment. Guard cells control the size of pores called stomata (singular stoma) in the
epidermis. Opening and closing the stomata allows plants to release or retain gases
including water vapor, oxygen, and carbon dioxide as needed.
Mesophyll
The middle mesophyll leaf layer is composed of a palisade mesophyll region and a spongy
mesophyll region. Palisade mesophyll contains columnar cells with spaces between the
cells. Most plant chloroplasts are found in palisade mesophyll. Chloroplasts
are organelles that contain chlorophyll, a green pigment that absorbs energy from sunlight
for photosynthesis. Spongy mesophyll is located below palisade mesophyll and is composed
of irregularly shaped cells. Leaf vascular tissue is found in the spongy mesophyll.
Vascular Tissue
Leaf veins are composed of vascular tissue. Vascular tissue consists of tube-shaped
structures called xylem and phloem that provide pathways for water and nutrients to flow
throughout the leaves and plant.
Specialized Leaves:

6. Some plants have leaves that are specialized to perform functions in addition
to photosynthesis. For example, carnivorous plants have developed specialized leaves
that work to lure and trap insects. These plants must supplement their diet with
nutrients gained from digesting animals because they inhabit areas where the soil
quality is poor. The Venus flytrap has mouth-like leaves, which close like a trap to
snare insects inside. Enzymes are then released in the leaves to digest the prey.
The leaves of pitcher plants are shaped like pitchers and brightly colored to attract
insects. The inside walls of the leaves are covered with waxy scales that make them very
slippery. Insects landing on the leaves may slip into the bottom of the pitcher-shaped
leaves and be digested by enzymes.

7. Leaf Imposters: Some animals
mimic leaves in order to avoid
detection. They camouflage themselves
as leaves as a defense mechanism to
escape predators. Other animals appear
as leaves to capture prey. Fallen foliage
from plants that lose their leaves in the
fall makes a perfect cover for animals
that have adapted to resemble leaves
and leaf litter. Examples of animals that
mimic leaves include the Amazonian
horned frog, leaf insects, and the Indian
leafwing butterfly.

8. Distinguish between the dorsiventral leaf and the isobilateral leaf.
Dorsiventral Leaf Isobilateral Leaf
1.The number of stomata is more on the abaxial epidermis than
the adaxial epidermis.
1.Almost equal number of stomata is present on the abaxial and
adaxial surfaces.
2.Mesophyll is differentiated into spongy and palisade
parenchyma.
2.Mesophyll layer is not differentiated into spongy and palisade
parenchyma.
3.Vascular bundles are large and vary in size as per the size of
veins.
3.Vascular bundles are similar in size, only the bundles near the
mid vein are large.
4.Bulliform cells are absent. 4.Bulliform cells are present.

9. Dorsiventral Leaf:
1. Internally the leaf is differentiated into upper and lower epidermis and mesophyll, which lies in
between the two epidermises.
2. The distribution of stomata is usually restricted to lower epidermis.
3. Mesophyll is composed, of palisade and spongy parenchyma. The palisade cells are elongated and
situated in transverse plane towards the upper epidermis. The spongy parenchyma cells are more or
less isodiametric in shape and occur in between the palisade and lower epidermis with profuse
intercellular spaces.
4. The vascular bundles, in the transverse section of leaf, are of different sizes and not arranged in a
transverse line. Ex. dicotyledonous leaf.
5. The vascular bundles are usually surrounded by bundle sheath consisting of a single layer of
parenchyma.

10. Isobilateral Leaf:
1. Internally the leaf is differentiated into upper and lower epidermis, and mesophyll, which occurs in
between the two epidermises.
2. The stomata are distributed on both the epidermises.
3. The mesophyll cells are composed of one type of cells, i.e. the cells are either more or less
isodiametric (simulate spongy parenchyma) or elongated (simulate palisade parenchyma); the cells lie in
between the upper and lower epidermis with little inter-cellular spaces.
4. In the transverse section of leaf the vascular bundles are more or less of same sizes and arranged in a
transverse line. Ex. monocotyledonous leaf.
5. The vascular bundles are usually surrounded by bundle sheath, which may be one or two layered. In
the latter case the outer sheath is composed of thin walled parenchyma cells. The cells of the inner
sheath are smaller in cross-sectional diametre and thick walled in comparison to the outer sheath. The
inner sheath is termed as mestome sheath and its cells are thickened with suberin.

11. Centric Leaf:
1. Internally the leaf is differentiated into epidermis and mesophyll; a single epidermis is
present all round the periphery and it encloses the mesopyll.
2. The stomata are distributed all round the circumference of epidermis.
3. The mesophyll may be composed of one type of cells or may be differentiated into
palisade and spongy parenchyma. In the latter case the palisade cells occur all round the
periphery of the cylindrical leaf (ex. Hakea).
4. In the transverse section of leaf the vascular bundles are present either in a line or in a
ring. Ex. onion, Hakea etc.

12. Thank you
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