Example of nervous tissue. (Photo credit: Wikipedia)
TISSUES
Plant Tissues
Meristematic Tissue
Permanent Tissue
Animal Tissue
Connective Tissue
Muscles
Epithelial
Nerves
Tissue is a group of cells. The cells in a tissue can be similar or different. The group
of cells thus formed carry specific functions. A group of different tissues make an organ.
Plant Tissues
Plant tissue culture is a practice used to develop plant under ste rile laboratory
conditions, often to produce clones of a plant. The production of exact copies of plants
that produce particularly good flowers, fruits, or have other desirable traits.
Advantages of Tissue Culture
• To quickly produce mature plants.
• The production of multiples of plants in the absence of seeds or necessary
pollinators to produce seeds.
• The regeneration of whole plants from plant cells that have been genetically
modified.
• The production of plants in sterile containers that allows them to be moved with
greatly reduced chances of transmitting diseases, pests, and pathogens.
• The production of plants from seeds that otherwise have very low chances of
germinating and growing, i.e.: orchids and nepenthes.
• To clean particular plant of viral and other infections and to quickly multiply
these plants as ‘cleaned stock’ for horticulture and agriculture.
Types of Plant Tissues
1) MERISTEMATIC TISSUE
Meristematic tissue is growth tissue and the location of most cell division. It is
known as undifferentiated tissue because cells in the meristematic tissue will
eventually become vascular, ground, or dermal tissue.
Location of meristematic tissue in plant body
Plants generally grow where meristematic tissue is present. At the tips of roots and
stems, the meristematic tissue is called the apical meristem.
Primary Growth
The primary growth of the plant occurs in the apical meristem. The growth in length of
a plant part is due to primary growth.
Secondary Growth
Lateral growth or growth in thickness in a plant is called secondary growth, which
occurs in lateral meristem tissue. Woody trees and shrubs display secondary growth
when the plants become enlarged and thickened.
2) PERMANENT TISSUE
When the cells formed by meristematic tissue take up a specific role and lose the ability
to divide. As a result, they form a permanent tissue. This process of taking up a
permanent shape, size, and a function is called differentiation. Cells of meristematic
tissue differentiate to form different types of permanent tissue.
Simple permanent tissues
These tissues are called simple because they are composed of similar types of cells
which have common origin and function. They are further classified into:
(II)Parenchyma
(III) Collenchyma
(IV) Sclerenchyma
1. Parenchyma
Parenchyma is Greek word where “parn” means besides and “enchien” means to pour.
Parenchyma is the most specialized primitive tissue. It mainly consist of thinwalled
cells which have intermolecular spaces between them. The cell wall is made up of
cellulose. Each parenchymatous cell is iso-diametric, spherical, or oval in shape. It is
widely distributed in various plant organs like root, stem, leaf, flowers and fruits. They
mainly occur in cortex epidermis, piths and mesophyll of leaves.
Function of Parenchyma
The main function of parenchymatous tissue is assimilation and storage of reserve food
materials like starch, fats and proteins. They also store waste products such as gums,
resins, and inorganic waste materials.
2. Collenchyma
Collenchyma is Greek word where “Collen” means gum and “enchyma” means infusion.
It is a living tissue of primary body like Parenchyma. Cells are thin-walled but possess
thickening of cellulose and pectin substances at the corners where number of cells join
together. This tissue gives a tensile strength to the plant and the cells are compactly
arranged and do not have intermolecular spaces. It occurs chiefly in hypodermis of
stems and leaves. It is absent in monocots and in roots.
Functions of Collenchyma
Collenchymatous tissue acts as a supporting tissue in stems of young plants. It provides
mechanical support, elasticity, and tensile strength to the plant body. It helps in
manufacturing sugar and storing it as starch. It is present in margin of leaves and
resists tearing effect of the wind.
3. Sclerenchyma
Sclerenchyma is Greek word where “Sclrenes” means hard and “enchyma” means
infusion. This tissue consists of thick-walled, dead cells. These cells have hard and
extremely thick secondary walls due to uniform distribution of ligin. Lignin deposition
is so thick that the cell walls become strong, rigid and impermeable to water.
Sclerenchymatous cells are closely packed without intra-cellular spaces between them.
Thus, they appear as hexagonal net in transverse section. The cells are cemented with
the help of lamella. The middle lamella is a wall that lies between adjacent cells.
Sclerenchymatous cells mainly occur in hypodermis, pricycle, secondary xylem and
phloem. They also occur in endocorp of almond and coconut. It is made of pectin,
lignin, protein.
Types of Sclerenchyma
Fibres- Fibres are long, elongated sclerenchyamtous cells with pointed ends.
Sclerides- Sclerenchymatous cells which are short and possess extremely thick,
lamellated, lignified walls with long singular piths. They are called sclerides.
Function of Sclerenchyma
The main function of Sclerenchymatous tissues is to give support to the plant.
2. Complex permanent tissue
A complex permanent tissue may be classified as a group of more than one type of
tissue having a common origin and working together as a unit to perform a function.
These tissues are concerned with transportation of water, mineral, nutrients and
organic substances. The important complex tissues in vascular plants are xylem,
phloem.
1. Xylem
Xylem is a chief, conducting tissue of vascular plants. It is responsible for conduction
of water and inorganic solutes.
1. Tracheids Trachids are elongated, tube-like dead cells with elongated endwalls.
End walls remain intact and possess piths. In transverse section, they usually
occur as polygonal cells and lignified walls.
2. Vessels – Vessels are placed one upon another. Their end walls are perforated.
They form long tubes or channels for conduction of water and minerals.
3. Xylem Parenchyma – Xylem Parenchymatous cells are living cells present in
xylem. They help in lateral conduction of organic solutes and storage reserves.
4. Xylem Fibres – Xylem Fibres are lignified fibres present in xylem which provide
mechanical strength to the plant body.
Xylem is a major conducting tissue of vascular plants. It serves in upward movement
of water and minerals from root to different parts of plant.
2. Phloem
Phloem is a chief conducting tissue of vascular plants. It is regarded as a living tissue
responsible for translocation of organic solutes.
1. Sieve tube – Sieve tubes are long tubular structures composed of elongated
Flax stem cross-section (Photo credit: Wikipedia)sieve tube elements placed one above other forming a continuous tube.
2. Companion cell – Companion cells are living cells always associated with sieve
tubes. Sieve tube elements and companion cells arrive from the same, initial
cell and therefore forms a single functional unit. Each companion cell shows
presence of fine piths with all the living components of the cell.
3. Phloem Parenchyma – These cells are living parenchymatous cells that are
present in phloem. These cells help in storage of food.
4. Phloem Fibres – Phloem fibres are formed by dead, sclerenchymatous fibres.
The main function of phloem is translocation of organic solutes from the leaves to the
storage organ and later from the storage organ to the growing part. Sieve tube allows
free diffusion of soluble, organic substances across sieve plates due to the presence of
large number of sieve pores.
Animal Tissues
Based on morphology, animal tissues can be grouped into four basic types. Multiple
tissue types comprise organs and body structures. While all animals can generally be
considered to contain the four tissue types, the manifestation of these tissues can differ
depending on the type of organism.
The four basic Animal Tissues are:
2. a) Connective tissue
Connective tissue is comprised of cells separated by non-living material, which is called
extra cellular matrix. As the name suggests connective tissues are meant to make
connections. Connective tissue holds other tissues together such as in the formation
of organs, and has the ability to stretch and contract passively. Bone, often referred to
as osseous tissue, and blood are examples of specialized connective tissues
b) Muscle tissue
Muscle cells form the active contractile tissue of the body known as muscle tissue.
Muscle tissue functions to produce force and cause motion, either locomotion or
movement within internal organs.
Types of Muscles
1.Smooth Muscle or Visceral Muscle found in inner linings of organs.
2 .Skeletal Muscle is attached to bone to provide movement.
3 .Cardiac Muscle is in heart and makes possible the pumping action of the heart.
3. c) Nervous tissue
Cells comprising the central nervous system and peripheral nervous system are
classified as neural tissue. In the central nervous system, neural tissue forms the brain,
cranial nerves and spinal cord and, in the peripheral nervous system, peripheral nerves
inclusive of the motor neurons. You can imagine the nervous tissue like an electrical
wiring in which the brain is the power generator, the spinal cord is the main line and
peipheral nerves are lines going to different organs.
4. d) Epithelial tissue
Epithelial tissues are formed by layers of cells that cover organ surfaces such as the
surface of the skin, the airways, and the inner lining of the digestive tract. The cells
comprising an epithelial layer are linked via semi-permeable, tight junctions.
Functions of Epithelial Tissues:
Protection of internal organs in case of intestine, kidney and heart and protection of
external organs also. In fact skin is an epithelial tissue covering the body. Skin is the
first line of defence against foreign substances. A burn victim doesn’t die because of
burn but because the whole defensive layer of skin is broken exposing the body to
various infections.
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