NCERT Textbook - Tissues Class 9 Notes | EduRev

 Page 1


From the last chapter, we recall that all living
organisms are made of cells. In unicellular
organisms, a single cell performs all basic
functions. For example, in Amoeba, a single
cell carries out movement, intake of food,
gaseous exchange and excretion. But in multi-
cellular organisms there are millions of cells.
Most of these cells are specialised to carry out
specific functions. Each specialised function
is taken up by a different group of cells. Since
these cells carry out only a particular function,
they do it very efficiently. In human beings,
muscle cells contract and relax to cause
movement, nerve cells carry messages, blood
flows to transport oxygen, food, hormones and
waste material and so on. In plants, vascular
tissues conduct food and water from one part
of the plant to other parts. So, multi-cellular
organisms show division of labour. Cells
specialising in one function are often grouped
together in the body. This means that a
particular function is carried out by a cluster
of cells at a definite place in the body. This
cluster of cells, called a tissue, is arranged and
designed so as to give the highest possible
efficiency of function. Blood, phloem and
muscle are all examples of tissues.
A group of cells that are similar in structure
and/or work together to achieve a particular
function forms a tissue.
6.1 Are Plants and Animals Made
of Same Types of Tissues?
Let us compare their structure and functions.
Do plants and animals have the same
structure? Do they both perform similar
functions?
There are noticeable differences between
the two. Plants are stationary or fixed – they
don’t move. Since they have to be upright, they
have a large quantity of supportive tissue. The
supportive tissue generally has dead cells.
Animals on the other hand move around
in search of food, mates and shelter. They
consume more energy as compared to plants.
Most of the tissues they contain are living.
Another difference between animals and
plants is in the pattern of growth. The growth
in plants is limited to certain regions, while this
is not so in animals. There are some tissues in
plants that divide throughout their life. These
tissues are localised in certain regions. Based
on the dividing capacity of the tissues, various
plant tissues can be classified as growing or
meristematic tissue and permanent tissue. Cell
growth in animals is more uniform. So, there
is no such demarcation of dividing and non-
dividing regions in animals.
The structural organisation of organs and
organ systems is far more specialised and
localised in complex animals than even in very
complex plants. This fundamental difference
reflects the different modes of life pursued by
these two major groups of organisms,
particularly in their different feeding methods.
Also, they are differently adapted for a
sedentary existence on one hand (plants) and
active locomotion on the other (animals),
contributing to this difference in organ system
design.
It is with reference to these complex animal
and plant bodies that we will now talk about
the concept of tissues in some detail.
6
T T T T TISSUES ISSUES ISSUES ISSUES ISSUES
Chapter
2020-21
Page 2


From the last chapter, we recall that all living
organisms are made of cells. In unicellular
organisms, a single cell performs all basic
functions. For example, in Amoeba, a single
cell carries out movement, intake of food,
gaseous exchange and excretion. But in multi-
cellular organisms there are millions of cells.
Most of these cells are specialised to carry out
specific functions. Each specialised function
is taken up by a different group of cells. Since
these cells carry out only a particular function,
they do it very efficiently. In human beings,
muscle cells contract and relax to cause
movement, nerve cells carry messages, blood
flows to transport oxygen, food, hormones and
waste material and so on. In plants, vascular
tissues conduct food and water from one part
of the plant to other parts. So, multi-cellular
organisms show division of labour. Cells
specialising in one function are often grouped
together in the body. This means that a
particular function is carried out by a cluster
of cells at a definite place in the body. This
cluster of cells, called a tissue, is arranged and
designed so as to give the highest possible
efficiency of function. Blood, phloem and
muscle are all examples of tissues.
A group of cells that are similar in structure
and/or work together to achieve a particular
function forms a tissue.
6.1 Are Plants and Animals Made
of Same Types of Tissues?
Let us compare their structure and functions.
Do plants and animals have the same
structure? Do they both perform similar
functions?
There are noticeable differences between
the two. Plants are stationary or fixed – they
don’t move. Since they have to be upright, they
have a large quantity of supportive tissue. The
supportive tissue generally has dead cells.
Animals on the other hand move around
in search of food, mates and shelter. They
consume more energy as compared to plants.
Most of the tissues they contain are living.
Another difference between animals and
plants is in the pattern of growth. The growth
in plants is limited to certain regions, while this
is not so in animals. There are some tissues in
plants that divide throughout their life. These
tissues are localised in certain regions. Based
on the dividing capacity of the tissues, various
plant tissues can be classified as growing or
meristematic tissue and permanent tissue. Cell
growth in animals is more uniform. So, there
is no such demarcation of dividing and non-
dividing regions in animals.
The structural organisation of organs and
organ systems is far more specialised and
localised in complex animals than even in very
complex plants. This fundamental difference
reflects the different modes of life pursued by
these two major groups of organisms,
particularly in their different feeding methods.
Also, they are differently adapted for a
sedentary existence on one hand (plants) and
active locomotion on the other (animals),
contributing to this difference in organ system
design.
It is with reference to these complex animal
and plant bodies that we will now talk about
the concept of tissues in some detail.
6
T T T T TISSUES ISSUES ISSUES ISSUES ISSUES
Chapter
2020-21
Lateral meristem
uestions
1. What is a tissue?
2. What is the utility of tissues in
multi-cellular organisms?
6.2 Plant Tissues
6.2.1 MERISTEMATIC TISSUE
• From the above observations, answer
the following questions:
1. Which of the two onions has longer
roots? Why?
2. Do the roots continue growing
even after we have removed their
tips?
3. Why would the tips stop growing
in jar 2 after we cut them?
The growth of plants occurs only in certain
specific regions. This is because the dividing
tissue, also known as meristematic tissue, is
located only at these points. Depending on
the region where they are present,
meristematic tissues are classified as apical,
lateral and intercalary (Fig. 6.2). New cells
produced by meristem are initially like those
of meristem itself, but as they grow and
mature, their characteristics slowly change and
they become differentiated as components of
other tissues.
Fig. 6.1: Growth of roots in onion bulbs
Activity ______________ 6.1
• Take two glass jars and fill them with
water.
• Now, take two onion bulbs and place
one on each jar, as shown in
Fig. 6.1.
• Observe the growth of roots in both
the bulbs for a few days.
• Measure the length of roots on day 1,
2 and 3.
• On day 4, cut the root tips of the onion
bulb in jar 2 by about 1 cm. After this,
observe the growth of roots in both the
jars and measure their lengths each
day for five more days and record the
observations in tables, like the table
below:
Length Day 1 Day 2 Day 3 Day 4 Day 5
Jar 1
Jar 2
Q
Apical meristem is present at the growing
tips of stems and roots and increases the
length of the stem and the root. The girth of
the stem or root increases due to lateral
meristem (cambium). Intercalary meristem
seen in some plants is located near the node.
Fig. 6.2: Location of meristematic tissue in plant body
Jar 1 Jar 2
TISSUES 69
Apical meristem
Intercalary meristem
2020-21
Page 3


From the last chapter, we recall that all living
organisms are made of cells. In unicellular
organisms, a single cell performs all basic
functions. For example, in Amoeba, a single
cell carries out movement, intake of food,
gaseous exchange and excretion. But in multi-
cellular organisms there are millions of cells.
Most of these cells are specialised to carry out
specific functions. Each specialised function
is taken up by a different group of cells. Since
these cells carry out only a particular function,
they do it very efficiently. In human beings,
muscle cells contract and relax to cause
movement, nerve cells carry messages, blood
flows to transport oxygen, food, hormones and
waste material and so on. In plants, vascular
tissues conduct food and water from one part
of the plant to other parts. So, multi-cellular
organisms show division of labour. Cells
specialising in one function are often grouped
together in the body. This means that a
particular function is carried out by a cluster
of cells at a definite place in the body. This
cluster of cells, called a tissue, is arranged and
designed so as to give the highest possible
efficiency of function. Blood, phloem and
muscle are all examples of tissues.
A group of cells that are similar in structure
and/or work together to achieve a particular
function forms a tissue.
6.1 Are Plants and Animals Made
of Same Types of Tissues?
Let us compare their structure and functions.
Do plants and animals have the same
structure? Do they both perform similar
functions?
There are noticeable differences between
the two. Plants are stationary or fixed – they
don’t move. Since they have to be upright, they
have a large quantity of supportive tissue. The
supportive tissue generally has dead cells.
Animals on the other hand move around
in search of food, mates and shelter. They
consume more energy as compared to plants.
Most of the tissues they contain are living.
Another difference between animals and
plants is in the pattern of growth. The growth
in plants is limited to certain regions, while this
is not so in animals. There are some tissues in
plants that divide throughout their life. These
tissues are localised in certain regions. Based
on the dividing capacity of the tissues, various
plant tissues can be classified as growing or
meristematic tissue and permanent tissue. Cell
growth in animals is more uniform. So, there
is no such demarcation of dividing and non-
dividing regions in animals.
The structural organisation of organs and
organ systems is far more specialised and
localised in complex animals than even in very
complex plants. This fundamental difference
reflects the different modes of life pursued by
these two major groups of organisms,
particularly in their different feeding methods.
Also, they are differently adapted for a
sedentary existence on one hand (plants) and
active locomotion on the other (animals),
contributing to this difference in organ system
design.
It is with reference to these complex animal
and plant bodies that we will now talk about
the concept of tissues in some detail.
6
T T T T TISSUES ISSUES ISSUES ISSUES ISSUES
Chapter
2020-21
Lateral meristem
uestions
1. What is a tissue?
2. What is the utility of tissues in
multi-cellular organisms?
6.2 Plant Tissues
6.2.1 MERISTEMATIC TISSUE
• From the above observations, answer
the following questions:
1. Which of the two onions has longer
roots? Why?
2. Do the roots continue growing
even after we have removed their
tips?
3. Why would the tips stop growing
in jar 2 after we cut them?
The growth of plants occurs only in certain
specific regions. This is because the dividing
tissue, also known as meristematic tissue, is
located only at these points. Depending on
the region where they are present,
meristematic tissues are classified as apical,
lateral and intercalary (Fig. 6.2). New cells
produced by meristem are initially like those
of meristem itself, but as they grow and
mature, their characteristics slowly change and
they become differentiated as components of
other tissues.
Fig. 6.1: Growth of roots in onion bulbs
Activity ______________ 6.1
• Take two glass jars and fill them with
water.
• Now, take two onion bulbs and place
one on each jar, as shown in
Fig. 6.1.
• Observe the growth of roots in both
the bulbs for a few days.
• Measure the length of roots on day 1,
2 and 3.
• On day 4, cut the root tips of the onion
bulb in jar 2 by about 1 cm. After this,
observe the growth of roots in both the
jars and measure their lengths each
day for five more days and record the
observations in tables, like the table
below:
Length Day 1 Day 2 Day 3 Day 4 Day 5
Jar 1
Jar 2
Q
Apical meristem is present at the growing
tips of stems and roots and increases the
length of the stem and the root. The girth of
the stem or root increases due to lateral
meristem (cambium). Intercalary meristem
seen in some plants is located near the node.
Fig. 6.2: Location of meristematic tissue in plant body
Jar 1 Jar 2
TISSUES 69
Apical meristem
Intercalary meristem
2020-21
SCIENCE 70
Cuticle
Epidermis
Collenchyma
Parenchyma
Phloem
Vascular bundle
Xylem
Fig. 6.3: Section of a stem
Cells of meristematic tissue are very active,
they have dense cytoplasm, thin cellulose walls
and prominent nuclei. They lack vacuoles. Can
we think why they would lack vacuoles? (You
might want to refer to the functions of vacuoles
in the chapter on cells.)
6.2.2 PERMANENT TISSUE
What happens to the cells formed by
meristematic tissue? They 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. Differentiation
leads to the development of various types of
permanent tissues.
3. Can we think of reasons why there
would be so many types of cells?
• We can also try to cut sections of plant
roots. We can even try cutting sections
of root and stem of different plants.
6.2.2 (i) SIMPLE PERMANENT TISSUE
A few layers of cells beneath the epidermis are
generally simple permanent tissue.
Parenchyma is the most common simple
permanent tissue. It consists of relatively
unspecialised cells with thin cell walls. They
are living cells. They are usually loosely
arranged, thus large spaces between cells
(intercellular  spaces) are found in this tissue
(Fig. 6.4 a). This tissue generally stores food.
Activity ______________ 6.2
• Take a plant stem and  with the help
of your teacher cut into very thin slices
or sections.
• Now, stain the slices with safranin.
Place one neatly cut section on a slide,
and put a drop of glycerine.
• Cover with a cover-slip and observe
under a microscope. Observe the
various types of cells and their
arrangement. Compare it with Fig. 6.3.
• Now, answer the following on the
basis of your observation:
1. Are all cells similar in structure?
2. How many types of cells can
be seen?
In some situations, it contains chlorophyll and
performs photosynthesis, and then it is called
chlorenchyma. In aquatic plants, large air
cavities are present in parenchyma to help
them float. Such a parenchyma type is called
aerenchyma.
The flexibility in plants is due to another
permanent tissue, collenchyma. It allows
bending of various parts of a plant like tendrils
and stems of climbers without breaking. It
also provides mechanical support. We can find
this tissue in leaf stalks below the epidermis.
The cells of this tissue are living, elongated
and irregularly thickened at the
corners. There is very little intercellular space
(Fig. 6.4 b).
2020-21
Page 4


From the last chapter, we recall that all living
organisms are made of cells. In unicellular
organisms, a single cell performs all basic
functions. For example, in Amoeba, a single
cell carries out movement, intake of food,
gaseous exchange and excretion. But in multi-
cellular organisms there are millions of cells.
Most of these cells are specialised to carry out
specific functions. Each specialised function
is taken up by a different group of cells. Since
these cells carry out only a particular function,
they do it very efficiently. In human beings,
muscle cells contract and relax to cause
movement, nerve cells carry messages, blood
flows to transport oxygen, food, hormones and
waste material and so on. In plants, vascular
tissues conduct food and water from one part
of the plant to other parts. So, multi-cellular
organisms show division of labour. Cells
specialising in one function are often grouped
together in the body. This means that a
particular function is carried out by a cluster
of cells at a definite place in the body. This
cluster of cells, called a tissue, is arranged and
designed so as to give the highest possible
efficiency of function. Blood, phloem and
muscle are all examples of tissues.
A group of cells that are similar in structure
and/or work together to achieve a particular
function forms a tissue.
6.1 Are Plants and Animals Made
of Same Types of Tissues?
Let us compare their structure and functions.
Do plants and animals have the same
structure? Do they both perform similar
functions?
There are noticeable differences between
the two. Plants are stationary or fixed – they
don’t move. Since they have to be upright, they
have a large quantity of supportive tissue. The
supportive tissue generally has dead cells.
Animals on the other hand move around
in search of food, mates and shelter. They
consume more energy as compared to plants.
Most of the tissues they contain are living.
Another difference between animals and
plants is in the pattern of growth. The growth
in plants is limited to certain regions, while this
is not so in animals. There are some tissues in
plants that divide throughout their life. These
tissues are localised in certain regions. Based
on the dividing capacity of the tissues, various
plant tissues can be classified as growing or
meristematic tissue and permanent tissue. Cell
growth in animals is more uniform. So, there
is no such demarcation of dividing and non-
dividing regions in animals.
The structural organisation of organs and
organ systems is far more specialised and
localised in complex animals than even in very
complex plants. This fundamental difference
reflects the different modes of life pursued by
these two major groups of organisms,
particularly in their different feeding methods.
Also, they are differently adapted for a
sedentary existence on one hand (plants) and
active locomotion on the other (animals),
contributing to this difference in organ system
design.
It is with reference to these complex animal
and plant bodies that we will now talk about
the concept of tissues in some detail.
6
T T T T TISSUES ISSUES ISSUES ISSUES ISSUES
Chapter
2020-21
Lateral meristem
uestions
1. What is a tissue?
2. What is the utility of tissues in
multi-cellular organisms?
6.2 Plant Tissues
6.2.1 MERISTEMATIC TISSUE
• From the above observations, answer
the following questions:
1. Which of the two onions has longer
roots? Why?
2. Do the roots continue growing
even after we have removed their
tips?
3. Why would the tips stop growing
in jar 2 after we cut them?
The growth of plants occurs only in certain
specific regions. This is because the dividing
tissue, also known as meristematic tissue, is
located only at these points. Depending on
the region where they are present,
meristematic tissues are classified as apical,
lateral and intercalary (Fig. 6.2). New cells
produced by meristem are initially like those
of meristem itself, but as they grow and
mature, their characteristics slowly change and
they become differentiated as components of
other tissues.
Fig. 6.1: Growth of roots in onion bulbs
Activity ______________ 6.1
• Take two glass jars and fill them with
water.
• Now, take two onion bulbs and place
one on each jar, as shown in
Fig. 6.1.
• Observe the growth of roots in both
the bulbs for a few days.
• Measure the length of roots on day 1,
2 and 3.
• On day 4, cut the root tips of the onion
bulb in jar 2 by about 1 cm. After this,
observe the growth of roots in both the
jars and measure their lengths each
day for five more days and record the
observations in tables, like the table
below:
Length Day 1 Day 2 Day 3 Day 4 Day 5
Jar 1
Jar 2
Q
Apical meristem is present at the growing
tips of stems and roots and increases the
length of the stem and the root. The girth of
the stem or root increases due to lateral
meristem (cambium). Intercalary meristem
seen in some plants is located near the node.
Fig. 6.2: Location of meristematic tissue in plant body
Jar 1 Jar 2
TISSUES 69
Apical meristem
Intercalary meristem
2020-21
SCIENCE 70
Cuticle
Epidermis
Collenchyma
Parenchyma
Phloem
Vascular bundle
Xylem
Fig. 6.3: Section of a stem
Cells of meristematic tissue are very active,
they have dense cytoplasm, thin cellulose walls
and prominent nuclei. They lack vacuoles. Can
we think why they would lack vacuoles? (You
might want to refer to the functions of vacuoles
in the chapter on cells.)
6.2.2 PERMANENT TISSUE
What happens to the cells formed by
meristematic tissue? They 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. Differentiation
leads to the development of various types of
permanent tissues.
3. Can we think of reasons why there
would be so many types of cells?
• We can also try to cut sections of plant
roots. We can even try cutting sections
of root and stem of different plants.
6.2.2 (i) SIMPLE PERMANENT TISSUE
A few layers of cells beneath the epidermis are
generally simple permanent tissue.
Parenchyma is the most common simple
permanent tissue. It consists of relatively
unspecialised cells with thin cell walls. They
are living cells. They are usually loosely
arranged, thus large spaces between cells
(intercellular  spaces) are found in this tissue
(Fig. 6.4 a). This tissue generally stores food.
Activity ______________ 6.2
• Take a plant stem and  with the help
of your teacher cut into very thin slices
or sections.
• Now, stain the slices with safranin.
Place one neatly cut section on a slide,
and put a drop of glycerine.
• Cover with a cover-slip and observe
under a microscope. Observe the
various types of cells and their
arrangement. Compare it with Fig. 6.3.
• Now, answer the following on the
basis of your observation:
1. Are all cells similar in structure?
2. How many types of cells can
be seen?
In some situations, it contains chlorophyll and
performs photosynthesis, and then it is called
chlorenchyma. In aquatic plants, large air
cavities are present in parenchyma to help
them float. Such a parenchyma type is called
aerenchyma.
The flexibility in plants is due to another
permanent tissue, collenchyma. It allows
bending of various parts of a plant like tendrils
and stems of climbers without breaking. It
also provides mechanical support. We can find
this tissue in leaf stalks below the epidermis.
The cells of this tissue are living, elongated
and irregularly thickened at the
corners. There is very little intercellular space
(Fig. 6.4 b).
2020-21
TISSUES 71
Fig. 6.4: Various types of simple tissues: (a) Parenchyma (b) Collenchyma (c) Sclerenchyma (i) transverse section,
(ii) longitudinal section.
Yet another type of permanent tissue is
sclerenchyma. It is the tissue which makes the
plant hard and stiff. We have seen the husk of
a coconut. It is made of sclerenchymatous
tissue. The cells of this tissue are dead. They
are long and narrow as the walls are thickened
due to lignin. Often these walls are so thick
that there is no internal space inside the cell
(Fig. 6.4 c). This tissue is present in stems,
around vascular bundles, in the veins of leaves
and in the hard covering of seeds and nuts. It
provides strength to the plant parts.
Activity ______________ 6.3
• Take a freshly plucked leaf of Rhoeo.
• Stretch and break it by applying
pressure.
• While breaking it, keep it stretched
gently so that some peel or skin
projects out from the cut.
• Remove this peel and put it in a petri
dish filled with water.
• Add a few drops of safranin.
• Wait for a couple of minutes and then
transfer it onto a slide. Gently place
a cover slip over it.
• Observe under microscope.
What you observe is the outermost layer
of cells, called epidermis. The epidermis is
usually made of a single layer of cells. In some
plants living in very dry habitats, the epidermis
may be thicker since protection against water
loss is critical. The entire surface of a plant has
an outer covering epidermis. It protects all the
parts of the plant. Epidermal cells on the aerial
a
Intercellular spaces
b
Wall thickenings
Nucleus
Vacuole
Cell wall
Narrow lumen
Lignified
thick wall
c (ii)
c (i)
Thick lignified
walls
Fig. 6.5: Guard cells and epidermal cells: (a)  lateral
view, (b) surface view
(a) (b)
Guard
cell
Stoma
Epidermal
cell
Guard
cells
parts of the plant often secrete a waxy, water-
resistant layer on their outer surface. This aids
in protection against loss of water, mechanical
injury and invasion by parasitic fungi. Since
it has a protective role to play, cells of
epidermal  tissue form a continuous layer
without intercellular spaces. Most epidermal
cells are relatively flat. Often their outer and
side walls are thicker than the inner wall.
We can observe small pores here and
there in the epidermis of the leaf. These pores
are called stomata (Fig. 6.5). Stomata are
enclosed by two kidney-shaped cells
called guard cells. They are necessary for
exchanging gases with the atmosphere.
Transpiration (loss of water in the form of
water vapour) also takes place through
stomata.
2020-21
Page 5


From the last chapter, we recall that all living
organisms are made of cells. In unicellular
organisms, a single cell performs all basic
functions. For example, in Amoeba, a single
cell carries out movement, intake of food,
gaseous exchange and excretion. But in multi-
cellular organisms there are millions of cells.
Most of these cells are specialised to carry out
specific functions. Each specialised function
is taken up by a different group of cells. Since
these cells carry out only a particular function,
they do it very efficiently. In human beings,
muscle cells contract and relax to cause
movement, nerve cells carry messages, blood
flows to transport oxygen, food, hormones and
waste material and so on. In plants, vascular
tissues conduct food and water from one part
of the plant to other parts. So, multi-cellular
organisms show division of labour. Cells
specialising in one function are often grouped
together in the body. This means that a
particular function is carried out by a cluster
of cells at a definite place in the body. This
cluster of cells, called a tissue, is arranged and
designed so as to give the highest possible
efficiency of function. Blood, phloem and
muscle are all examples of tissues.
A group of cells that are similar in structure
and/or work together to achieve a particular
function forms a tissue.
6.1 Are Plants and Animals Made
of Same Types of Tissues?
Let us compare their structure and functions.
Do plants and animals have the same
structure? Do they both perform similar
functions?
There are noticeable differences between
the two. Plants are stationary or fixed – they
don’t move. Since they have to be upright, they
have a large quantity of supportive tissue. The
supportive tissue generally has dead cells.
Animals on the other hand move around
in search of food, mates and shelter. They
consume more energy as compared to plants.
Most of the tissues they contain are living.
Another difference between animals and
plants is in the pattern of growth. The growth
in plants is limited to certain regions, while this
is not so in animals. There are some tissues in
plants that divide throughout their life. These
tissues are localised in certain regions. Based
on the dividing capacity of the tissues, various
plant tissues can be classified as growing or
meristematic tissue and permanent tissue. Cell
growth in animals is more uniform. So, there
is no such demarcation of dividing and non-
dividing regions in animals.
The structural organisation of organs and
organ systems is far more specialised and
localised in complex animals than even in very
complex plants. This fundamental difference
reflects the different modes of life pursued by
these two major groups of organisms,
particularly in their different feeding methods.
Also, they are differently adapted for a
sedentary existence on one hand (plants) and
active locomotion on the other (animals),
contributing to this difference in organ system
design.
It is with reference to these complex animal
and plant bodies that we will now talk about
the concept of tissues in some detail.
6
T T T T TISSUES ISSUES ISSUES ISSUES ISSUES
Chapter
2020-21
Lateral meristem
uestions
1. What is a tissue?
2. What is the utility of tissues in
multi-cellular organisms?
6.2 Plant Tissues
6.2.1 MERISTEMATIC TISSUE
• From the above observations, answer
the following questions:
1. Which of the two onions has longer
roots? Why?
2. Do the roots continue growing
even after we have removed their
tips?
3. Why would the tips stop growing
in jar 2 after we cut them?
The growth of plants occurs only in certain
specific regions. This is because the dividing
tissue, also known as meristematic tissue, is
located only at these points. Depending on
the region where they are present,
meristematic tissues are classified as apical,
lateral and intercalary (Fig. 6.2). New cells
produced by meristem are initially like those
of meristem itself, but as they grow and
mature, their characteristics slowly change and
they become differentiated as components of
other tissues.
Fig. 6.1: Growth of roots in onion bulbs
Activity ______________ 6.1
• Take two glass jars and fill them with
water.
• Now, take two onion bulbs and place
one on each jar, as shown in
Fig. 6.1.
• Observe the growth of roots in both
the bulbs for a few days.
• Measure the length of roots on day 1,
2 and 3.
• On day 4, cut the root tips of the onion
bulb in jar 2 by about 1 cm. After this,
observe the growth of roots in both the
jars and measure their lengths each
day for five more days and record the
observations in tables, like the table
below:
Length Day 1 Day 2 Day 3 Day 4 Day 5
Jar 1
Jar 2
Q
Apical meristem is present at the growing
tips of stems and roots and increases the
length of the stem and the root. The girth of
the stem or root increases due to lateral
meristem (cambium). Intercalary meristem
seen in some plants is located near the node.
Fig. 6.2: Location of meristematic tissue in plant body
Jar 1 Jar 2
TISSUES 69
Apical meristem
Intercalary meristem
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SCIENCE 70
Cuticle
Epidermis
Collenchyma
Parenchyma
Phloem
Vascular bundle
Xylem
Fig. 6.3: Section of a stem
Cells of meristematic tissue are very active,
they have dense cytoplasm, thin cellulose walls
and prominent nuclei. They lack vacuoles. Can
we think why they would lack vacuoles? (You
might want to refer to the functions of vacuoles
in the chapter on cells.)
6.2.2 PERMANENT TISSUE
What happens to the cells formed by
meristematic tissue? They 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. Differentiation
leads to the development of various types of
permanent tissues.
3. Can we think of reasons why there
would be so many types of cells?
• We can also try to cut sections of plant
roots. We can even try cutting sections
of root and stem of different plants.
6.2.2 (i) SIMPLE PERMANENT TISSUE
A few layers of cells beneath the epidermis are
generally simple permanent tissue.
Parenchyma is the most common simple
permanent tissue. It consists of relatively
unspecialised cells with thin cell walls. They
are living cells. They are usually loosely
arranged, thus large spaces between cells
(intercellular  spaces) are found in this tissue
(Fig. 6.4 a). This tissue generally stores food.
Activity ______________ 6.2
• Take a plant stem and  with the help
of your teacher cut into very thin slices
or sections.
• Now, stain the slices with safranin.
Place one neatly cut section on a slide,
and put a drop of glycerine.
• Cover with a cover-slip and observe
under a microscope. Observe the
various types of cells and their
arrangement. Compare it with Fig. 6.3.
• Now, answer the following on the
basis of your observation:
1. Are all cells similar in structure?
2. How many types of cells can
be seen?
In some situations, it contains chlorophyll and
performs photosynthesis, and then it is called
chlorenchyma. In aquatic plants, large air
cavities are present in parenchyma to help
them float. Such a parenchyma type is called
aerenchyma.
The flexibility in plants is due to another
permanent tissue, collenchyma. It allows
bending of various parts of a plant like tendrils
and stems of climbers without breaking. It
also provides mechanical support. We can find
this tissue in leaf stalks below the epidermis.
The cells of this tissue are living, elongated
and irregularly thickened at the
corners. There is very little intercellular space
(Fig. 6.4 b).
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TISSUES 71
Fig. 6.4: Various types of simple tissues: (a) Parenchyma (b) Collenchyma (c) Sclerenchyma (i) transverse section,
(ii) longitudinal section.
Yet another type of permanent tissue is
sclerenchyma. It is the tissue which makes the
plant hard and stiff. We have seen the husk of
a coconut. It is made of sclerenchymatous
tissue. The cells of this tissue are dead. They
are long and narrow as the walls are thickened
due to lignin. Often these walls are so thick
that there is no internal space inside the cell
(Fig. 6.4 c). This tissue is present in stems,
around vascular bundles, in the veins of leaves
and in the hard covering of seeds and nuts. It
provides strength to the plant parts.
Activity ______________ 6.3
• Take a freshly plucked leaf of Rhoeo.
• Stretch and break it by applying
pressure.
• While breaking it, keep it stretched
gently so that some peel or skin
projects out from the cut.
• Remove this peel and put it in a petri
dish filled with water.
• Add a few drops of safranin.
• Wait for a couple of minutes and then
transfer it onto a slide. Gently place
a cover slip over it.
• Observe under microscope.
What you observe is the outermost layer
of cells, called epidermis. The epidermis is
usually made of a single layer of cells. In some
plants living in very dry habitats, the epidermis
may be thicker since protection against water
loss is critical. The entire surface of a plant has
an outer covering epidermis. It protects all the
parts of the plant. Epidermal cells on the aerial
a
Intercellular spaces
b
Wall thickenings
Nucleus
Vacuole
Cell wall
Narrow lumen
Lignified
thick wall
c (ii)
c (i)
Thick lignified
walls
Fig. 6.5: Guard cells and epidermal cells: (a)  lateral
view, (b) surface view
(a) (b)
Guard
cell
Stoma
Epidermal
cell
Guard
cells
parts of the plant often secrete a waxy, water-
resistant layer on their outer surface. This aids
in protection against loss of water, mechanical
injury and invasion by parasitic fungi. Since
it has a protective role to play, cells of
epidermal  tissue form a continuous layer
without intercellular spaces. Most epidermal
cells are relatively flat. Often their outer and
side walls are thicker than the inner wall.
We can observe small pores here and
there in the epidermis of the leaf. These pores
are called stomata (Fig. 6.5). Stomata are
enclosed by two kidney-shaped cells
called guard cells. They are necessary for
exchanging gases with the atmosphere.
Transpiration (loss of water in the form of
water vapour) also takes place through
stomata.
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SCIENCE 72
Recall which gas is required for
photosynthesis.
Find out the role of transpiration in plants.
Epidermal cells of the roots, whose function
is water absorption, commonly bear long hair-
like parts that greatly increase the total
absorptive surface area.
In some plants like desert plants,
epidermis has a thick waxy coating of cutin
(chemical substance with waterproof quality)
on its outer surface. Can we think of a reason
for this?
Is the outer layer of a branch of a tree
different from the outer layer of a young stem?
As plants grow older, the outer protective
tissue undergoes certain changes. A strip of
secondary meristem located in the cortex forms
layers of cells which constitute the cork. Cells
of cork are dead and compactly arranged
without intercellular spaces (Fig. 6.6). They
also have a substance called suberin in their
walls that makes them impervious to gases
and water.
is a distinctive feature of the complex plants,
one that has made possible their survival in
the terrestrial environment. In Fig. 6.3 showing
a section of stem, can you see different types
of cells in the vascular bundle?
Xylem consists of tracheids, vessels, xylem
parenchyma (Fig. 6.7 a,b,c) and xylem fibres.
Tracheids and vessels have thick walls, and
many are dead cells when mature. Tracheids
and vessels are tubular structures. This allows
them to transport water and minerals
vertically. The parenchyma stores food. Xylem
fibres are mainly supportive in function.
Phloem is made up of five types of cells:
sieve cells, sieve tubes, companion cells,
phloem fibres and the phloem parenchyma
[Fig. 6.7 (d)]. Sieve tubes are tubular cells with
perforated walls. Phloem transports food from
leaves to other parts of the plant. Except
phloem fibres, other phloem cells are living cells.
6.2.2 (ii) COMPLEX PERMANENT TISSUE
The different types of tissues we have discussed
until now are all made of one type of cells,
which look like each other. Such tissues are
called simple permanent tissue. Yet another
type of permanent tissue is complex tissue.
Complex tissues are made of more than one
type of cells. All these cells coordinate to
perform a common function. Xylem and
phloem are examples of such complex tissues.
They are both conducting tissues and
constitute a vascular bundle. Vascular tissue
Fig. 6.6: Protective tissue
Cork cells
Ruptured epidermis
Nucleus
Cytoplasm
Pits
Pit
(a) Tracheid (b) Vessel (c) Xylem parenchyma
Fig. 6.7: Types of complex tissue
Sieve plate
Sieve tube
Phloem
parenchyma
Companion cell
(d) Section of phloem
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