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The outermost layer of
the leaf is the epidermis. It
consists of the upper and lower
epidermis, which are present on
either side of the leaf. Botanists
call the upper side the adaxial
surface (or adaxis) and the lower
side the abaxial surface (or
abaxis). The epidermis aids in the
regulation of gas exchange. It
contains stomata, which are
openings through which the
exchange of gases takes place.
Two guard cells surround
each stoma, regulating its
opening and closing. Guard cells
are the only epidermal cells to
contain chloroplasts.
The epidermis is usually one cell layer thick. However, in plants that
grow in very hot or very cold conditions, the epidermis may be several
layers thick to protect against excessive water loss from transpiration.
A waxy layer known as the cuticle covers the leaves of all
plant species. The cuticle reduces the rate of water loss from the leaf
surface. Other leaves may have small hairs (trichomes) on the leaf
surface. Trichomes help to avert herbivory by restricting insect
movements or by storing toxic or bad-tasting compounds. They can
also reduce the rate of transpiration by blocking air flow across the
Trichomes give leaves a fuzzy appearance as in this (a)
sundew (Drosera sp.). Leaf trichomes include (b) branched trichomes
on the leaf of Arabidopsis lyrata and (c) multibranched trichomes on
a mature Quercus marilandica leaf.
Below the epidermis of dicot leaves are layers of cells known as the
mesophyll, or "middle leaf." The mesophyll of most leaves typically
contains two arrangements of parenchyma cells: the palisade
parenchyma and spongy parenchyma . The palisade parenchyma
(also called the palisade mesophyll) aids in photosynthesis and has
column-shaped, tightly-packed cells. It may be present in one, two,
or three layers. Below the palisade parenchyma are loosely-
arranged cells of an irregular shape.
These are the cells of the spongy parenchyma (or spongy mesophyll).
The air space found between the spongy parenchyma cells allows
gaseous exchange between the leaf and the outside atmosphere
through the stomata. In aquatic plants, the intercellular spaces in the
spongy parenchyma help the leaf float. Both layers of the mesophyll
contain many chloroplasts.
A. (top) The central mesophyll is
sandwiched between an upper
and lower epidermis. The
mesophyll has two layers: an
upper palisade layer and a lower
spongy layer. Stomata on the leaf
underside allow gas exchange. A
waxy cuticle covers all aerial
surfaces of land plants to
minimize water loss. (b) (bottom)
These leaf layers are clearly
visible in the scanning electron
micrograph. The numerous small
bumps in the palisade
parenchyma cells are
chloroplasts.
B. The bumps protruding from the
lower surface of the leaf are
glandular trichomes.
Similar to the stem, the leaf contains vascular bundles composed
of xylem and phloem . The xylem consists of tracheids and
vessels, which transport water and minerals to the leaves. The
phloem transports the photosynthetic products from the leaf to
the other parts of the plant. A single vascular bundle, no matter
how large or small, always contains both xylem and phloem
tissues.
This scanning electron micrograph
shows xylem and phloem in the leaf
vascular bundle.
Coniferous plant species that thrive in cold
environments, such as spruce, fir, and pine, have leaves
that are reduced in size and needle-like in appearance.
These needle-like leaves have sunken stomata and a
smaller surface area, two attributes that aid in reducing
water loss. In hot climates, plants such as cacti have
succulent leaves that help to conserve water. Many
aquatic plants have leaves with wide lamina that can float
on the surface of the water; a thick waxy cuticle on the
 The epidermis consists of the upper and lower epidermis; it aids in the
regulation of gas exchange via stomata.
 The epidermis is one layer thick, but may have more layers to
prevent transpiration.
 The cuticle is located outside the epidermis and protects against water
loss; trichomes discourage predation.
 The mesophyll is found between the upper and lower epidermis; it aids
in gas exchange and photosynthesis via chloroplasts.
 The xylem transports water and minerals to the leaves;
the phloem transports the photosynthetic products to the other parts of
the plant.
 Plants in cold climates have needle-like leaves that are reduced in size;
plants in hot climates have succulent leaves that help to conserve water.
KEY POINTS
●Cuticle a noncellular protective covering outside the epidermis of many
invertebrates and plants
● Trichome a hair- or scale-like extension of the epidermis of a plant
● Mesophyll the inner tissue (parenchyma) of a leaf, containing many
chloroplasts.
Michael Angelo Enriquez
Ma. Nazarene A. Fulgueras
Trixie Mae Candelaria
Laurence Stephen Carpina
Rica Mae Custodio

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Leaf structure

  • 1.
  • 2.
  • 3. The outermost layer of the leaf is the epidermis. It consists of the upper and lower epidermis, which are present on either side of the leaf. Botanists call the upper side the adaxial surface (or adaxis) and the lower side the abaxial surface (or abaxis). The epidermis aids in the regulation of gas exchange. It contains stomata, which are openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing. Guard cells are the only epidermal cells to contain chloroplasts.
  • 4. The epidermis is usually one cell layer thick. However, in plants that grow in very hot or very cold conditions, the epidermis may be several layers thick to protect against excessive water loss from transpiration. A waxy layer known as the cuticle covers the leaves of all plant species. The cuticle reduces the rate of water loss from the leaf surface. Other leaves may have small hairs (trichomes) on the leaf surface. Trichomes help to avert herbivory by restricting insect movements or by storing toxic or bad-tasting compounds. They can also reduce the rate of transpiration by blocking air flow across the
  • 5. Trichomes give leaves a fuzzy appearance as in this (a) sundew (Drosera sp.). Leaf trichomes include (b) branched trichomes on the leaf of Arabidopsis lyrata and (c) multibranched trichomes on a mature Quercus marilandica leaf.
  • 6. Below the epidermis of dicot leaves are layers of cells known as the mesophyll, or "middle leaf." The mesophyll of most leaves typically contains two arrangements of parenchyma cells: the palisade parenchyma and spongy parenchyma . The palisade parenchyma (also called the palisade mesophyll) aids in photosynthesis and has column-shaped, tightly-packed cells. It may be present in one, two, or three layers. Below the palisade parenchyma are loosely- arranged cells of an irregular shape. These are the cells of the spongy parenchyma (or spongy mesophyll). The air space found between the spongy parenchyma cells allows gaseous exchange between the leaf and the outside atmosphere through the stomata. In aquatic plants, the intercellular spaces in the spongy parenchyma help the leaf float. Both layers of the mesophyll contain many chloroplasts.
  • 7. A. (top) The central mesophyll is sandwiched between an upper and lower epidermis. The mesophyll has two layers: an upper palisade layer and a lower spongy layer. Stomata on the leaf underside allow gas exchange. A waxy cuticle covers all aerial surfaces of land plants to minimize water loss. (b) (bottom) These leaf layers are clearly visible in the scanning electron micrograph. The numerous small bumps in the palisade parenchyma cells are chloroplasts. B. The bumps protruding from the lower surface of the leaf are glandular trichomes.
  • 8. Similar to the stem, the leaf contains vascular bundles composed of xylem and phloem . The xylem consists of tracheids and vessels, which transport water and minerals to the leaves. The phloem transports the photosynthetic products from the leaf to the other parts of the plant. A single vascular bundle, no matter how large or small, always contains both xylem and phloem tissues. This scanning electron micrograph shows xylem and phloem in the leaf vascular bundle.
  • 9. Coniferous plant species that thrive in cold environments, such as spruce, fir, and pine, have leaves that are reduced in size and needle-like in appearance. These needle-like leaves have sunken stomata and a smaller surface area, two attributes that aid in reducing water loss. In hot climates, plants such as cacti have succulent leaves that help to conserve water. Many aquatic plants have leaves with wide lamina that can float on the surface of the water; a thick waxy cuticle on the
  • 10.  The epidermis consists of the upper and lower epidermis; it aids in the regulation of gas exchange via stomata.  The epidermis is one layer thick, but may have more layers to prevent transpiration.  The cuticle is located outside the epidermis and protects against water loss; trichomes discourage predation.  The mesophyll is found between the upper and lower epidermis; it aids in gas exchange and photosynthesis via chloroplasts.  The xylem transports water and minerals to the leaves; the phloem transports the photosynthetic products to the other parts of the plant.  Plants in cold climates have needle-like leaves that are reduced in size; plants in hot climates have succulent leaves that help to conserve water. KEY POINTS ●Cuticle a noncellular protective covering outside the epidermis of many invertebrates and plants ● Trichome a hair- or scale-like extension of the epidermis of a plant ● Mesophyll the inner tissue (parenchyma) of a leaf, containing many chloroplasts.
  • 11. Michael Angelo Enriquez Ma. Nazarene A. Fulgueras Trixie Mae Candelaria Laurence Stephen Carpina Rica Mae Custodio