Tissues
By : Ashutosh Lal (TGT Science, KV Etawah)
Introduction
·
Living organisms in
this world comprise of cells.
·
There are unicellular
as well as multicellular organisms present in this world.
·
In unicellular
organisms, the only single cell is capable of performing several functions such
as Respiration, Digestion and Clearing of the cell.
·
In multicellular
organisms, there is a division of labor. There are different types as well as
groups of cells that perform different functions in a multicellular
organism. For Example,
In animals muscle cells are responsible for causing movement, nerve cells are
responsible for carrying messages and signals from one part of the body to
another and blood is responsible for transportation of food and oxygen to
different parts of the body.
·
In plants, there are
vascular tissues that are responsible for carrying food and water two different
parts of a plant.
The Formation of Tissues
·
Cells form groups
cells that need to perform a single task often group together.
·
This grouping of cells
together to perform a function efficiently is called a Tissue.
·
For Example,
Muscles and Blood.
·
The tissue cells have
the same structure and they perform the same function.
Tissues of Plants and Animals
|
Plant Tissues |
Animal Tissues |
|
Plants do not move so their tissues are predominantly the ones
that provide support to them so that they can stand erect. |
Animals need more energy as compared to plants because they
are not stationary. Their tissues are the ones that can support movement. |
|
These tissues are made up of dead cells because dead cells can
also provide mechanical strength to the plants and do not require much
maintenance. |
The tissues in case of animals are made up of living cells so
that they can move and perform several functions. |
|
Only certain parts of the plant can grow. The tissues present
in such regions of and divide themselves and form new tissues. |
Cells in animals grow uniform early and not only in certain
regions of the body. |
|
The structure of plant tissues is not very specialized as
compared to animals |
The organs and organ systems in animals are highly developed. |
|
Apical Meristem |
Lateral Meristem |
Intercalary Meristem |
|
·
They
are responsible for the growth of stems and roots in the plants ·
They
are found on the tips of the roots and stems. |
·
They
are responsible for increasing the circumference of the middle part of the
stem and hence are found there. |
·
These
tissues are present at internodes or stem regions between the places at which
leaves attach. |
Permanent Tissue
·
The cells that are
formed by the meristematic tissues often have to take a certain role in the
plant and thus, they lose their ability to divide and form more cells. They
then become the permanent tissues of the plants.
·
Differentiation - The process by which cells of the meristematic tissues convert
themselves into a permanent tissue by taking a fixed shape, size and function
is called differentiation.
·
Types of Permanent Tissues:
o Simple Permanent Tissues
o Complex Permanent Tissues
·
Simple Permanent Tissues are of five types:
o Parenchyma
o Chlorenchyma
o Aerenchyma
o Collenchyma
o Sclerenchyma
|
Parenchyma |
Collenchyma |
Sclerenchyma |
|
These tissues are responsible for photosynthesis, storage of
food, gaseous exchange and floating of plants. |
These tissues are responsible for providing flexibility to the
plants so that they can bend easily. |
These tissues are responsible for making plants hard and
rigid. |
|
They are a group of living cells with cell wall made of
cellulose. |
They are a group of living cells with cell wall made of
cellulose and pectin. |
They are made up of dead cells having cell wall made of
lignin. |
|
The parenchyma cells have large intercellular spaces between
them. |
They have a little intercellular space in between them. |
The cells do not have any intercellular spaces. |
|
There are thin walls that surround each cell. |
The cells present in these tissues are broad and irregularly
thick at corners. |
The cells have a long structure with thick walls. |
|
They are found in leaves and newly formed branches. |
They are present in leaves and stems of a plant. |
They are found in stems, veins of the leaves and coverings of
nuts and seeds. |
Complex Permanent Tissues
Complex Permanent Tissues comprise of different kinds of cells. These different types of cells coordinate with each other and perform a common function in these tissues. Two Complex Permanent Tissues are - Xylem and Phloem
Similarities between
Xylem and Phloem
·
Their main function is
to carry food and water in the plant.
·
Both have a vascular
bundle which is a conductive tissue in plants that helps them survive in
different environmental conditions.
Xylem
Xylem is made up of
dead cells having a thick cell lining. It consists of following elements-
·
Tracheids and Vessels – They have broad tubular structure so that we can allow
transportation of food and water in the plants vertically.
·
Xylem Parenchyma – It stores food and helps in transportation of water
horizontally in the plants.
·
Xylem Fibers –
They support transportation
Phloem : Phloem is made up
of living cells and it allows the movement of food from leaves to other parts
of the plant. It has the following elements –
Sieve Tubes –
Broad shaped cells with porous walls
·
Companion Cells – They facilitate the functions of the sieve tubes
·
Phloem Fibers – Provide flexibility to the phloem
·
Phloem Parenchyma – Stores starch and proteins
|
Properties |
Xylem |
Phloem |
|
Made of |
Dead Cells |
Living Cells |
|
Cell wall thickness |
Thick |
Thin |
|
Cell wall material |
Lignin (rigid) |
Celluloses |
|
Permeability |
Impermeable |
Permeable |
|
Cytoplasm |
None |
Cytoplasm lining |
|
Transports… |
Water & minerals |
Food |
|
Carried to…. |
Leaves |
Growing parts & storage organs |
|
Direction of flow |
Upwards |
Up & down |
|
Tissue alos has … |
Fibres |
Companion cells |
