ANATOMY OF FLOWERING PLANTS
INTRODUCTION
Plants have cells as the basic unit, cells are organised into tissues and in turn the tissues are organised into organs. Different organs in a plant show differences in their internal structure. Within angiosperms, the monocots and dicots are also seen to be anatomically different. Internal structures also show adaptations to diverse environments.
THE TISSUES
· A group of cells having a common origin and
generally performing common function are called tissues.
· Meristematic tissues is a simple tissues
composed of group of analogous and immature cells which can divide and form new
cells. The meristem which occurs at tips of roots and shoots are called apical meristem.
· Intercalary meristem occurs between mature
tissues especially in grasses. Both apical meristems and intercalary meristems
are primary meristems because they appear beforehand in life of a plants and
help to form the primary plants body.
· The meristem which occurs on the sides and takes
part in adding circumference of the plants are called Side meristem.
· Intrafascicular cambium in the primary side
meristem. Vascular cambium, cork cambium are secondary meristem.
· The cells that have come structurally and
functionally specialized and lose the capability to divide are called endless
tissues. Endless tissues having all cells analogous in structure and function
are called simple endless tissues and those having different kinds of cells are
called complex tissues.
Anatomy of Flowering Plants notes for NEET
Parenchyma
is a simple endless living tissues which is made up of thin-walled isodiametric
cells. Each cell encloses a large central vacuole and supplemental cytoplasm
containing nexus. They're plant in non-woody and soft areas of stem, root,
leaves, fruits and flowers. They store the food and give turgidity to softer
corridor of plants.
· Collenchyma
consists of cells which are important thickened at corner due to cellulose,
hemicellulose and pectin. Oval, globular or polygonal frequently contain
chlorophyll. They give mechanical support to the growing corridor of the plants
like youthful stem.
· Sclerenchymas
are probative tissues having largely thick walled cells with little or no
protoplasm due to deposit of cellulose or lignin. They're of two types fibres
and sclereids. They give mechanical support to mature plants organs to tolerate
bending, shearing, contractionetc.
Complex Tissues – Xylem and phloem constitute the complex tissues in plants and work together as a unit.
Anatomy of Flowering Plants NCERT Notes PDF
Epidermal Tissues System
· It forms the remotest covering of whole plants
body, which consists of epidermal cells, stomata, epidermal accessories
(trichomes and hairs).
· Epidermis is single layered, parenchymatous with
waxy thick layers of cuticle to help water loss.
· Stomata is present in epidermis of leaves. It
regulates the transpiration and gassy exchange. In dicots, stomata are bean-
shaped having two guard cells closing the stomatal severance. In monocots,
stoma is dumbbell- shaped. Guard cells contain chloroplasts and help in opening
and ending of stomata.
· Guard cells are girdled by attachment cells. The
stomatal orifice, guard cells and the girding attachment cells are together
called stomatal outfit.
Dicots (Bean shaped) Monocots (Dumb-bell shaped)
· Epidermis also contains a number of hairs. Root
hairs are unicellular extension of epidermal cells. Trichomes are present on
stems, which are multicellular, fanned orun-branched precluding water loss due
to transpiration.
The ground Tissues System
· All the tissues between epidermis and vascular
pack forms the ground tissues. It consists of simple endless tissues.
Parenchyma is present in pericycle, cortex, pith and medullary shafts in stem
and roots.
In leaves the
mesophyll, chloroplast containing cell, forms the ground tissues.
The Vascular Tissues
System
The vascular system
consists of complex tissues, xylem and phloem that together form vascular
packets. When xylem and phloem within a vascular pack are arranged in alternate
manner on different diameters, the arrangement are called radial as in roots.
When xylem and phloem are positioned at the same compass of vascular pack, it's
called conjoint as in stem and leaves.
Dicotyledonous Root
· The remotest subcaste of dicot root is epidermis
containing unicellular root hairs.
· The cortex consists of several layers of
thin-walled parenchyma cells.
· The inmost subcaste of cortex is called
endodermis having waxy material suberin as casparian strips, which is
impermeable to water.
Monocotyledonous Root
· The deconstruction of the monocot root is
analogous to the dicot root in numerous felitations.
· It has epidermis, cortex, endodermis, pericycle, vascular packets and pith. As compared to the dicot root which have smaller xylem packets
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Dicotyledonous Stem
· Epidermis is covered with a thin subcaste of
cuticle and may have Trichomes and stomata.
· Cortex The cortex is made up of the multiple
layers of cells including hypodermis, middle subcaste of parenchyma cells and
inmost subcaste called endodermis.
· Endodermis cells are rich in bounce grains and
are called the bounce jacket. Pericycle is present on the inner side of
endodermis. Layers of radially placed parenchyma between the vascular packets
are called medullary shafts.
· A large number of vascular packets are arranged
in a ring. Each vascular pack is conjoint, open. Protoxylem is endarch
Monocotyledonous Stem
· The hypodermis is made up of sclerenchyma.
Vascular packets are conjoint, closed and scattered. Each vascular pack is
girdled by a sclerenchymatous pack jacket.
· Phloem parenchyma is absent. Water- containing depressions are present within the vascular packets.
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Dorsiventral
(Dicotyledonous) Leaf
· The splint lamella of a dorsiventral splint has
3 corridor epidermis, mesophyll and vascular system.
· The upper epidermis is called adaxial epidermis
and lower bone is called abaxial epidermis. Further number of stomata are
present on the abaxial epidermis.
· There are two types of cells in the mesophyll
precipice parenchyma and spongy parenchyma. The precipice parenchyma is placed
adaxially.
· The spongy parenchyma is positioned below the
precipice parenchyma and extends to the lower epidermis. There are multitudinous
large spaces and air depressions between the cells of spongy parenchyma.
· Vascular packets are girdled by a subcaste of
thick-walled pack jacket cells.
ALSO CHECK:
Isobilateral
(Monocotyledonous) Leaf
· Stomata are present on both the shells of an
isobilateral splint. The mesophyll isn't discerned into precipice and spongy
parenchyma.
· Some adaxial epidermal cells in meadows are modified into large, empty cells called bulliform cells. When the bulliform cells absorb water, they come bloated. So the splint face is exposed.
During
water stress, when the bulliform cells come limp, the leaves coil inwards to
minimize water loss.
Anatomy of Flowering Plants NEET notes PDF
SECONDARY GROWTH
The increase in
circumference of a plants body is called secondary growth. The tissues involved
in secondary growth are vascular cambium and cork cambium.
Vascular Cambium
In case of youthful
stem vascular cambium is present in patches as a single subcaste between the
xylem and phloem. It forms a complete ring at a after stage.
Exertion of the Cambial
Ring
· The cambial ring becomes active and begins to
cut off new cells, both towards the inner and the external sides.
· The cells which are cut off towards pith develop
into secondary xylem. The cells which are cut off towards fringe develop into
secondary phloem.
· The cambium is more active on the inner side
than on the external. As a result, the quantum of secondary xylem produced is
further than secondary phloem. The primary and secondary phloems get
gradationally crushed due to the continued conformation and accumulation of
secondary xylem.
· At some places, the cambium forms a narrow band
of parenchyma, which passes through the secondary xylem and the secondary
phloem in the radial directions. These are the secondary medullary shafts.
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Spring wood and Sap wood
· Cambium is veritably active during the spring
season, but less active during the layoffs. Hence, during spring; a large
number of xylem rudiments are formed having wider vessels. During downtime,
less xylem rudiments are formed having narrow vessels.
· The wood formed during summer is called spring
wood. The wood formed during downtime is called afterlife wood.
· The two kinds of wood appear as alternate
concentric rings in transverse section of a box of a tree. These are called
periodic rings and give information about age of the tree.
Heartwood and sapwood
In old trees, the
lesser part of secondary xylem is dark in colour, hard, and resistant to
attacks by microorganisms and nonentity. This region is made of dead rudiments
with largely lignified walls. This wood is called heartwood. The heartwood
gives mechanical support but doesn't conduct water.
The supplemental part
of the secondary xylem is smoothly coloured. This is known as sapwood. It helps
in conduction of water and minerals.
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Cork Cambium
· Meristematic tissues which develops in the
cortex region is called cork cambium or phellogen.
· The phellogen cuts off cells on both sides. The
external cells separate to form cork or phellem while the inner cells separate
into secondary cortex or phelloderm.
· Phellogen, phellem and phelloderm are
inclusively called periderm.
· Due to exertion of the cork cambium, pressure
builds up on the remaining layers supplemental to phellogen. These layers
gradationally die and fall off.
Lenticels
· At certain regions, the phellogen cuts off
nearly arranged parenchymatous cells on the external side rather of cork cells.
These parenchymatous cells soon rupture the epidermis, forming a lens- shaped
openings called lenticels.
· Lenticels permit the exchange of feasts between
the external atmosphere and the internal tissues of the stem.
Anatomy of Flowering Plants NCERT Notes PDF
Secondary
Growth in Roots
The vascular cambium of the dicot root originates from the tissues located just below the phloem packets. A portion of pericycle tissues present above the protoxylem forms a nonstop crimpy ring. It gradationally becomes indirect. Rest of the way are analogous as in dicot stem.
· Secondary growth takes place in stems and roots
of gymnosperms. No secondary growth occurs in monocots.
anatomy of flowering plants notes pdf