Introduction to Tissues

How would you react if I say that your body is made up of building

blocks? I bet you would just laugh it off! If you look at things from a

science perspective, then the building blocks that I am talking about

are nothing but the cells and tissue. Even plants are made of cells and

tissue! Every living organism is made up of cells that form the basic

unit of life. Let us know more about these tissues!

Tissue

Living organisms that are found in the world are classified into

unicellular and multicellular organisms. So, if you see unicellular

organisms like Amoeba, Paramecium, diatoms, bacteria, etc. have

only one cell. They do not have tissue level of organization. Even in

some lower order animals, tissue differentiation is absent.

This means that cells form groups. But they do not perform a definite

function. But if you see multicellular higher order animals like

humans, dogs, etc. different groups of cells perform different specific

functions.

If a cell is called the basic unit of life, then a group of cells together

make up the tissues. These groups of cells have a common origin with

a similar structure. And the groups of cells perform a definite function.

So, in simple terms, tissues can be defined as a group of cells

performing similar functions.

Tissues represent a level of organization in living organisms. Both

plants and animals have tissues. But the kinds of tissues that are

present in both the living organisms are different. If you see in

animals, groups of muscle cells together form the muscle tissue.

Similarly, groups of plant cells form the plant tissue.

(Source Science-resources.co.uk)

Types of Tissues

Tissues are classified into two types. They are Plant tissues and

Animal Tissues.

Plant Tissues

When you see plants and animals, there is quite a bit of difference that

is clearly visible. And therefore the internal cell structure of both these

organisms also differs. In plants, the tissues that are present have to

give structural support to the plant, as plants are stationary.

The pattern of growth that is seen in plants is also limited to certain

areas. There are some tissues in plants that divide throughout their life.

These are generally restricted to certain regions. Therefore we can

aptly differentiate the plant tissues on the basis of the dividing

capacity. According to this classification, there are two types of plant

tissues. They are :

● Meristematic tissue

● Permanent tissue

Animal Tissues

Animals move from one place to the other in search of food, shelter

etc. Therefore the body shows many movements. In order for the body

to perform these activities, the cells and tissues perform definite

functions. You can observe that the growth in animals is generally

uniform.

Apart from this, in animals, the tissue level organization is very

complex, with many organs and organ systems. Each system has

specialized tissues performing specialized functions in a synchronized

manner. Animal tissues are broadly classified as:

● Epithelial tissues

● Muscular tissues

● Connective Tissues

● Nervous Tissues

Solved Question for You

Q: Do unicellular organisms show a true division of labour?

Ans. No. Division of labour is absent in unicellular organism, as only

one cell performs all the essential functions. Multicellular organisms,

which have tissues. exhibit true division of labour.

Meristematic Tissue

Have seen plants grow from small saplings to bigger plants and then

trees? Don’t you think they generally grow from the top? Yes, they

do. There are some specialized cells in plants that are not

differentiated and help in the growth of the plants. These cells in a

plant can be young and have the ability to divide continuously. There

is a special name for these cells, which are called the meristem cells.

The tissue that these meristem cells form in plants is called as the

meristematic tissue.

Meristematic Tissue in Plants

Meristematic tissue or meristems, as they are also called are tissues

that have the ability to enlarge, stretch and differentiate into other

types of cells as they mature. The cells of this tissue are generally

young and immature, with the power of continuous division.

Meristematic cells are all living cells. The meristematic cells can be

oval or rounded or polygonal in shape. They have a large nucleus with

no vacuoles. Intercellular space between cells is absent. The cells are

also small in size but have a high capacity of cell division.

Learn more about the different type of Animal Tissues here.

Types of Meristematic Tissue

Depending on the occurrence of the meristematic tissue on the plant

body, we can classify the meristems into three types. They are:

(Source: BiologyDiscussion)

● Apical Meristems – These meristems are located on the tip of

the root, stem etc. They help in the growth of the root system as

well as the shoot system. The various cell divisions along with

the cellular enlargement help in the growth of the stem above

the ground and the growth of the root below the ground.

● Intercalary Meristems – The intercalary meristems are located

at the internodes or the base of the leaves. The intercalary

meristems help in increasing the length of the internode. This is

usually seen in monocotyledonous plants.

● Lateral Meristems – The lateral meristems are present on the

lateral side of the stem and root of a plant. These meristems

help in increasing the thickness of the plants. The vascular

cambium and the cork cambium are good examples of a lateral

meristematic tissue.

Learn more about Epithelial Tissue, Connective Tissue, Muscular and

Nervous Tissue here.

Solved Questions For You

Q. Apical meristems are found in animals. Is it True or False?

Ans. False. Apical meristems are found in plants. They help in the

increase of the height of a plant.

Q: Stem of date palm increases in girth due to activity of

a. Intercalary Meristem

b. Apical Meristem

c. Both of the above

d. None of the above

Sol: Most monocots either have no secondary growth or else

anomalous secondary growth of some type. For example, palm trees

increase their trunk diameter due to division and enlargement of

parenchyma cells, which is termed as ‘diffuse secondary growth’.

In some other monocot stems with anomalous secondary growth, a

cambium forms but it produces vascular bundles and parenchyma

internally and just parenchyma externally. Some monocot stems

increase in diameter due to the activity of a primary thickening

meristem, which derives itself from the apical meristem.

The stem of date palm increases in girth due to the activity of apical

meristem and not because of intercalary meristem and lateral meristem

(involves is the normal secondary growth of dicots). Thus, option B is

correct.

Permanent Tissue

Have you ever wondered how the tips of tall plants get water that is

absorbed by the roots, deep down in the ground? Is there any special

mechanism by which this happens? Well! It is not exactly a

mechanism, but a group of specialized cells and tissues that help to

carry out this function. You have already learned about one type of

plant tissue, i.e. the Meristematic Tissues(Read). Plants also have

other types of tissue called the permanent tissue in them. It is one of

these tissues that help in the movement of water from the root to the

stem.

Permanent Tissue in Plants

In simple words, the permanent tissues in a plant are those tissues that

contain nondividing cells. The cells are also modified to perform

specific functions in the plants. The cells of the permanent tissue are

derived from the meristematic tissue.

The permanent tissue cells are also fully differentiated. The cells are

large and a definite shape and size. You can see intercellular spaces

being present in between the cells. Large vacuoles are also present

inside these cells. The metabolism that occurs in the cells of the

permanent tissue is fairly at a lower rate.

The permanent tissue in plants mainly helps in providing support,

protection as well as in photosynthesis and conduction of water,

minerals, and nutrients. Permanent tissue cells may be living or dead.

Types of Permanent Tissues

Permanent tissues can be classified into two types. They are:

● Simple permanent tissue

● Complex Permanent tissue

Simple Permanent Tissues

These tissues are simple. They are made up of only one type of cell.

Here, all the cells that make up the tissue are similar and have the

same structure, with the same type parts. Simple permanent tissues are

again classified into three main types. They are parenchyma,

collenchyma, and sclerenchyma.

● Parenchyma – The cells of this tissue are living, with thin cell

walls. Cells can be oval or round in shape. They have a large

central vacuole and a dense cytoplasm. The parenchyma tissue

is located in the soft parts of the plant such as cortex and pith.

It mainly acts as a packing tissue, providing mechanical

support. It also helps in the storage of food. Based on the

specific functions, parenchyma can be further classified into

Aerenchyma and Chlorenchyma.

● Collenchyma – These cells are living cells and have an

elongated shape. The corners of the cell wall are thickened.

There is very little intercellular space present. The collenchyma

tissue can be located in the leaf stalks, below the epidermis etc.

Its main function is to provide flexibility to the plants as well as

mechanical support.

● Sclerenchyma – The cells of the sclerenchyma tissue are dead.

The cell wall is very thick due to the deposition of lignin. The

cells of this tissue can be in different shapes and sizes. They are

generally located in the leaf veins, hard coverings of the seeds

and can also be found surrounding the vascular bundle. The

main function of the sclerenchymatic tissue is to provide

rigidity and mechanical support to the plant body. They also

make the plant stiff and hard.

What are Different Types of Plant Tissues here?

Complex Permanent Tissue

The complex permanent tissues are made up of more than one type of

cell. They coordinate together to perform the same specialized

functions in the plant body. They are classified into two types –

Xylem and Phloem

● Xylem – The xylem tissue is responsible for the conduction of

water and minerals from the roots to the leaves and stem. It

also provides support to the plants. It has four elements. They

are tracheids, vessels, xylem parenchyma and xylem fibres.

● Phloem – This complex permanent tissue helps in the

translocation of food that is prepared by photosynthesis in the

leaves to various parts of the plant. Phloem consists of four

elements. They are sieve tubes, companion cells, phloem fibres

and phloem parenchyma.

Solved Questions For You

Q: Name the tissues that are present in the various parts of the plants.

Ans. The names are as follows:

● Husk of a coconut – Sclerenchyma

● Cortex of the root – Parenchyma

● Veins of the leaves- Sclerenchyma

● Vascular bundle – Xylem and Phloem

Epithelial Tissue

You know that your body is made up of many cells and tissues.

Epithelial tissue is one of them. The skin that covers your body is

made up of epithelial tissue. Let us know more about this tissue in

detail.

What Is Epithelial Tissue?

Epithelial tissues are animal tissues. The cells that are present in these

tissues show all the characteristics of animal cells. The cells are

eukaryotic with a nucleus and membrane-bound organelles. Animal

cells do not have a cell wall and this is what gives them flexibility.

The cells of the tissue can take up different shapes to become

specialized and perform specific functions.

And so, epithelial tissues have cells that have different shapes, sizes,

and arrangements. Accordingly, they are classified into different

types. Epithelial cells can be seen in different parts of the body. They

cover the body’s surface and also line the internal body organs and

body cavities.

Browse more Topics under Tissues

● Introduction to Tissues

● Meristematic Tissue

● Permanent Tissue

● Epithelial Tissue

● Connective Tissues

● Muscular and Nervous Tissues

Their functions include protection of the underlying tissues,

absorption of substances, regulation of chemicals between the tissues

and body cavity etc. And they are able to perform such varied

functions since they do not have a definite shape

What is the Connection between Blood and Bones? Learn about

Connective Tissue here.

Types of Epithelial Tissue

The different types of epithelial tissues are given below. Let us learn a

little bit about each type. You will see how their shape adapts

according to the functions that they perform.

● Squamous Epithelium – These are thin, flat cells that are

closely packed. The squamous epithelial cells line the cavities

of the mouth, esophagus, alveoli, and blood vessels. This tissue

gives protection against mechanical injury and also blocks the

entry of germs. If the squamous epithelium is arranged in many

layers, it is a compound squamous tissue called the stratified

squamous epithelium. We find these kinds of tissues in the skin

and also the lining of the esophagus.

● Cuboidal Epithelium – These cells are cuboidal in shape. They

are found in the salivary glands, kidney tubules, sweat glands,

etc. Their main function includes absorption, secretion, and

excretion. If the cuboidal epithelium is arranged in many layers

it forms the stratified cuboidal epithelium. It is found on the

inner side of the pancreatic ducts and salivary glands. They

mainly help in protection.

● Columnar Epithelium – The columnar epithelium has cells that

are pillar-like and column-like. We can find them in the lining

of the stomach and intestine. Its functions include absorption

and secretion.

● Ciliated Epithelium – When the columnar epithelial tissues

have cilia, then they are ciliated epithelium. They are present in

the lining of the trachea, kidney tubules, etc. The rhythmic

movement of the cilia helps in the movement of material in one

direction.

● Glandular Epithelium – These are modified columnar epithelial

tissues. They are large cells that present in the tear glands,

sweat glands etc. Their main function is secretion.

Learn more about Meristematic Tissue here.

Solved Questions For You

Q: Name the type of epithelium found in the lining of the following

organs.

Ans. The names are as follows:

● Lining of the small intestine – Columnar epithelium

● The lining of the kidney tubules – Cuboidal epithelium

● Lining of blood vessels – Squamous epithelium

● Respiratory tract – Ciliated Epithelium

Connective Tissues

The human body contains an average of 5.5 litres of blood. The bones

make up around 15% of the body’s weight. But what is the connection

between bones and blood? The answer lies in the word itself!

Actually, both blood and bones form a part of the connective tissue in

animals. Let us educate ourselves about the various types of

connective tissue. 

Connective Tissue

Connective tissues connect and help hold our body together. They

provide internal support as well as give and maintain form to the body.

They protect the body. The connective tissue can be found everywhere

in the body. The connective tissue mainly consists of blood, bones,

and areolar tissue.

Blood

Blood is a fluid connective tissue. It consists of a liquid matrix called

the plasma, in which blood cells are present. So it can be said blood is

an important lifeline. It travels all around the body in specialized

blood vessels. Blood has many functions to play in the body.

Primarily, it helps in the transport of gases, nutrients, hormones as

well as the elimination of the waste materials.

There are three types of blood cells that are found in the plasma. They

are the Red blood cells (RBC) or Erythrocytes; White blood cells or

Leucocytes (WBC) and Thrombocytes or Blood Platelets. The RBCs

and the WBC’s are the living components of the blood.

The RBCs have a pigment called hemoglobin, due to which blood

appears red in colour. The WBCs help in protecting the body by

attacking any foreign body that enters into the body, while the blood

platelets are responsible for clotting of blood.

Browse more Topics under Tissues

● Introduction to Tissues

● Meristematic Tissue

● Permanent Tissue

● Epithelial Tissue

● Muscular and Nervous Tissues

Bones

If blood is a fluid connective tissue, bones are the hard connective

tissue. Bones give support and framework to the body. They protect

the internal organs and the muscle tissue attached to the bones helps in

movement. The bone tissue is strong and non-flexible. The cells are

embedded inside a hard matrix, which is made up of proteins, calcium

and phosphorous.

The ligament is the tissue that connects two bones. It is an elastic

tissue which has considerable strength. Ligaments have a very little

matrix. The bones are also connected to muscles. The tendons are the

types of tissues that connect the bones and muscles. They are fibrous

tissues and have great strength. But the flexibility of the tendon tissue

is limited.

Similarly, cartilage is another type of connective tissue that has a solid

matrix. It contains proteins and sugars. The cartilage tissue has widely

spaced cells. Cartilage is also an important connective tissue as it

helps in smoothening the bone surfaces at the joints. Cartilage is also

present in the trachea, nose, ears, and larynx.

Areolar Tissue

The areolar tissue is a loose connective tissue that can be seen

between the skin and muscles; in the bone marrow as well as around

the blood vessels and nerves. The areolar tissue fills the spaces

between the different organs and connects the skin to the underlying

muscles. And therefore, it provides support to the internal organs as

well as help in the repair of tissues.

Learn more about Muscular and Nervous Tissue.

The areolar tissue consists of many types of fibres and cells. Among

the cells are the adipocytes. These adipocyte cells together make the

adipose tissue or the fat tissue. It is in these cells that fat is stored in

the form of fat globules. Due to the storage of fat, the adipose tissue

acts as an insulator.

Solved Questions For You

Q. Name the connective that joins two bones.

Ans. The names are as follows:

a. Ligament

b. Tendon

c. Areolar tissue

d. Cartilage

Ans. The correct option is “A”. The ligament is the connective tissue

that joins two bones.

Q. Fat is stored in which tissue? What is its function?

Ans. Fat is stored in the adipose tissue. It acts as an insulator.

Muscular and Nervous Tissues

Something that differentiates animals from other organisms is the

presence of the nervous tissue and muscular tissue. Can you imagine a

man or even an animal without these tissues? If they are not present,

the very basic function of thinking and reacting to stimuli will be

absent. And man cannot survive! Let us explore these tissues in detail.

Suggested Videos

Muscular Tissue

(Source: Learnscience.org)

This is a tissue that helps in the movement of the various body parts.

They are generally attached to the bones, and thus help in movement.

There are three types of muscular tissue. They are:

● Smooth Muscle – These muscle cells do not have striations or

stripes. Hence they are called smooth muscle cells. They are

also called as involuntary muscles. The cells have a single

nucleus and the cells are spindle-shaped. They are found in the

walls of the hollow organs like the stomach, uterus etc. Their

main function is to move the material through the body. The

involuntary muscles are controlled by the brain.

● Skeletal Muscle – The skeletal muscles have stripes or

striations. Hence they are also called as the striated muscles.

These muscles are voluntary muscles that are controlled by us.

They mainly help in the locomotion and are attached to the

skeleton. The cells are long and cylindrical with many nuclei.

The skeletal muscles can be found in the muscles of the limbs,

face, neck etc.

● Cardiac Muscle – This is a muscle that is found only in the

heart. The rhythmic contractions of this muscle help in the

pumping of blood through the blood vessels to various parts of

the body. The brain controls this muscle and is an involuntary

muscle. The cells of this muscle tissue are branched and

cylindrical with a single nucleus and striations present.

Video on Nervous Tissue

Nervous Tissue

The nervous tissue is a highly specialized tissue that is present in the

animals. They help in transmitting messages from the brain to various

parts of the body and vice versa.

The nervous tissue is made of come specialized cells called neurons or

nerve cells. They can receive and transmit electrical impulses from

different areas of the body to specific locations. The nervous tissue

cells are present in the brain, spinal cord, and the nerves.

Browse more Topics under Tissues

● Introduction to Tissues

● Meristematic Tissue

● Permanent Tissue

● Epithelial Tissue

● Connective Tissues

The neuron is a specialized cell in the nervous system. It consists of

mainly three parts, the cell body or the cyton, the axon and the

dendrites. The dendrites of one neuron are attached to the dendrites of

the other neuron and thus help in the transmission of impulses or

messages.

Solved Questions For You

Q: Which tissue is responsible for the movement in our body?

Ans. The muscular tissue is responsible for the locomotion/movement

in our body. These are present in all animals to enable movement.

Q: Where is the nervous tissue located in the body?

Ans: The nervous tissue is made up of specialized cells called

neurons. The nervous tissue is located in the brain, spinal cord, and

nerves. These cells collectively make up the nervous tissue.