Class 9 Science Chapter - 6th Tissues Notes, Previous Year Questions & NCERT Solutions

Class 9 Science

Chapter - 6th

Tissues

Notes, Previous Year Questions & NCERT Solutions

----- Notes -----

Living organisms are comprise of cells.
Living organisms can be unicellular or multicellular.
In unicellular organisms, the 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 labour. There are different types as well as groups of cells that perform different functions in a multicellular organism.

The Formation of Tissues

𑇐 The groups of cells that perform a single task.

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 the 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 the 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 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 specialised as compared to animals	The organs and organ systems in animals are highly developed.

Plant Tissues

Figure 1: Types of Plant Tissues

Meristematic Tissue

Only certain parts of a plant tend to grow. The tissues located in such parts are called meristematic tissues.
They can divide themselves and form new tissues.
They have a thin cell wall made of cellulose.
They have a dense nucleus and cytoplasm but lack vacuoles.
They can further be classified differently based on the areas of the plants where they are located -
- Apical
- Lateral
- Intercalary

Figure 2: Location of meristematic tissue

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 of stem regions between the places at which leaves attach.

Why are there no vacuoles in the intercalary meristem?

Vacuoles are responsible for the storage of food in the water. The intercalary tissues do not store them. They are rather responsible for manufacturing them.
Moreover, vacuoles contain sap which provides rigidity to a cell. This property of vacuoles may not allow the intercalary tissues to divide and manufacture new cells. Hence vacuoles are not present in them.

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 permanent tissue by taking a fixed shape, size and function is called differentiation.
Types of Permanent Tissues:
- Simple Permanent Tissues
- Complex Permanent Tissues
Simple Permanent Tissues are of five types:
- Parenchyma
- Chlorenchyma
- Aerenchyma
- Collenchyma
- Sclerenchyma

Figure 3: Simple Permanent Tissue

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 a cell wall made of cellulose.	They are a group of living cells with a cell wall made of cellulose and pectin.	They are made up of dead cells having a 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 the leaves and stems of a plant.	They are found in stems, veins of the leaves and coverings of nuts and seeds.

Chlorenchyma

These tissues are similar to that of parenchyma but they also contain chlorophyll in them.
Due to the presence of chlorophyll, they are capable of performing the process of photosynthesis in plants.

Aerenchyma

They are found in aquatic plants.
They are also similar in structure to that of the parenchyma but they have large air cavities in them.
These cavities allow the aquatic plants to float in water.

What is Lignin?

The cell walls of dead cells have a substance called lignin in them which provides rigidity to the cells. Lignin acts as the cement for the cells.

Epidermis

The outermost layer of the cell is known as the Epidermis.

It covers the entire plant.
It is a thin layer of single cells but in places with less water, the epidermis of the plants can become thick in order to avoid frequent water loss.
The cells are flat and they have no intercellular spaces between them.
The outer walls of the epidermal cells are thick and the inner walls are thin.
The epidermal cells often have long hair-like structures in roots which facilitate the absorption of water.
The main function of the epidermis is to protect the plants from fungi, water loss and any injuries by secreting a wax-like water-resistant substance called a Cuticle on the surface of the plants which protects the plants.

Figure 4: Epidermis

Stomata

Stomata are pore-like structures that are present in the epidermis of the leaves.
These pores are enclosed by two cells that have a similar shape as a kidney. These are called Guard Cells of Stomata. Guard cells are modified epidermal cells.
Guard cells are responsible for the exchange of gases and transpiration.

Transpiration

Figure 5: Transpiration

The plant cells sometimes have extra they lose it in the form of water that evaporates through stomata. This process is called Transpiration.

Role of Transpiration in Plants

Exchange of Gases - Plants absorb carbon dioxide and release oxygen through transpiration.
Prevent the Plants from Overheating - The leaves absorb sunlight during the process of photosynthesis. Some of it is used in the photosynthesis process while the rest is radiated as Heat Energy. We know that absorption of water causes cooling of the surrounding area. Therefore transpiration keeps the leaves cool.
Transportation of Food and Water in Plants - The roots of the plants absorb minerals and water present in the soil through transpiration and they are then distributed in the plant through the transpiration stream.
Movement of Water in Plants – As plants lose water in the form of water vapours, the density of water in leaves becomes low. So the water from the higher density areas such as the roots move up to lower density areas through a force called Transpirational Pull.

Which gas is necessary for the process of photosynthesis?

Carbon dioxide gas is necessary for the process of photosynthesis. Plants use carbon dioxide along with water and sunlight to produce glucose in the process of photosynthesis. Plants take in carbon dioxide and release oxygen as a byproduct of the photosynthesis process.

Why do plants in desert areas have a waxy coating of cutting over them?

The epidermis cells of plants that are found in deserts have a waxy coating of cutting over them because it prevents water loss from the surface of plants since water is already scarce in such areas.

Why are the branches of old trees different from the stems of a new plant?

As a plant grows older the meristematic cells start covering the upper layer of the plants instead of the epidermis.
These are the dead cells that have no special function in the plants but to provide rigidity. They make the branches of the plants thick.
This is often called the Bark or the thick cork of the tree.
The bark of the trees contains a substance called Suberin which makes it waterproof and does not allow gaseous exchanges.

Complex Permanent Tissues

Complex Permanent Tissues comprise 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.

Figure 6: 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 the following elements-

Tracheids and Vessels – They have a 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 the transportation of water horizontally in the plants.
Xylem Fibres – 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 Fibres – Provide flexibility to the phloem
Phloem Parenchyma – Stores starch and proteins

Characteristic	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 also has …	Fibres	Companion cells

Animal Tissue

Figure 7: Types of Animal Tissues

1. Epithelial Tissue

They are the protective tissues of the human body. They cover many organs and cavities that are present inside the body.

Where are the epithelial tissues found in the human body?
- The lining of the blood vessels
- The lining of the mouth
- Kidney tubules
- Skin
- Lung alveoli
Structure and functions of the epithelial tissues -
- The main function of the epithelial tissues is to act as a barrier and separate different organs and systems from each other.
- There is no space between the cells of epithelial tissues
- The cells are permeable. This makes it possible for them to exchange materials between different parts of the body and also between the body and the external environment.
- The epithelial tissues remain separated from the tissues beneath them because of a thin membrane over them.

Figure 8: Types of Epithelium

Different types of epithelium tissues	Simple Squamous	Stratified Squamous	Columnar	Ciliated Columnar	Cuboidal	Glandular
Structure	They have delicate cell lining and possess a flat thin structure	The epithelium Squamous cells are arranged in several layers	They are the column-like shape tissues	Columnar epithelial tissues which have Cilia present on them	They are cube-shaped cells which are involved in absorption and secretion.	These are special gland cells that can secrete substances
Found in	Alveoli and bowman’s capsule- nephron in the kidney	Skin	Intestine	Respiratory system	Kidney tubules	Sweat glands in the skin

2. Connective Tissues

Structure and function of connective tissues
- They are loosely bound cells present in an intercellular Matrix.
- This matrix can be of different types – Dense, Rigid, Fluid or Jelly-like.
- Depending upon the functionality of the connective tissue, the nature of the matrix varies.
Examples of Connective Tissues

Figure 9: Connective Tissues

Blood

The main function of blood is to transport gases, food, waste materials and hormones in the body.
Therefore, blood has a fluid Matrix present in it which is called Plasma.
The plasma contains red blood cells, white blood cells and blood platelets.
The RBC has haemoglobin pigment which carries oxygen to tissues.
White blood cells fight diseases and platelets are involved in the clotting of blood when injured.
The plasma also contains proteins and hormones in it.

Lymph

Lymph is a colourless fluid that carries white blood cells throughout the human body in lymphatic vessels. There are lymphoid organs present in the body that produce lymph and together form the lymphatic system. Some of them are lymph nodes and tonsils.

Figure 10: Lymph Capillaries

Lymph is similar to blood except for a few differences:

It contains only white blood cells.
It contains less amount of blood proteins, calcium and phosphorus but more glucose.
It flows in one direction only.
Lymph moves in the body through its normal function, unlike blood which is pumped by the heart.

Constituents of Lymph:

Lymph Plasma – Lymph Plasma carries infection-fighting proteins along with other substances such as water, calcium and phosphorus.

Lymph Corpuscles – Lymph Corpuscles comprises white blood cells. Red blood cells and platelets are not present in lymph.

Functions of Lymph:

It carries oxygen and minerals to the cells in the body and carries back carbon dioxide and waste materials back into the blood.
It keeps the body cells moist.
It maintains the volume of the blood.
It helps in eliminating harmful bacteria and viruses from the body and hence is responsible for the immunity of human beings.
It absorbs fats from the intestine and transports them throughout the body.

Bones

Bones form a framework of the body over which the muscles are wrapped together.
The bone tissue is strong and inflexible.
Therefore, the bone cells are present in a rigid matrix that is formed from calcium and phosphorus.

Cartilage

Cartilage is present over the joints of the bones and provides them with a smooth structure.
For Example in the nose tip and ear pinna, trachea, larynx.
They contain a solid matrix made of protein and sugar. They have a homogenous matrix.
It provides support and flexibility to various parts of our body.

Ligaments

A ligament connects two bones together.
It has an elasticity that facilitates the connection.
The cells of ligaments have a little matrix.

Tendons

The tendon tissues are responsible for connecting bones and muscles together.
They have limited flexibility but very great strength.

Areolar

This tissue acts as a filter in between the spaces present inside the organs of the body.
It helps in repairing other tissues as well.
It is found in the skin and bone marrow.

Components of the Areolar Connective Tissue

Figure 12 Components of the areolar connective tissue

1. Cells

Fat Cells (Adipocytes) – They are responsible for the secretion of lipids.
Fibroblasts – They are present in the highest amount in areolar tissues. They are responsible for the secretion of fibres.
Mast Cells – They release histamine that plays a role in allergic reactions
Macrophages – They eat any germs or infectious cells in the body
Plasma Cells – They produce antibodies

2. Fibres

Collagen Fibres – They provide tensile strength to the tissue
Elastin Fibres – They provide elasticity to the tissue
Ground Substance – It is a fluid matrix that holds cells and fibres of the tissue

Adipose

Fats are stored in our body in the adipose tissues.
They are found below the skin and between the organs of the body.
Provides cushioning to the organs.

3. Muscular Tissue

It is made up of muscle fibres which are long cells.
It allows movements in our bodies.
They contain special proteins called Contractile Proteins. These proteins cause contraction and relaxation of the muscles.

There are two kinds of muscles found in our body - Voluntary Muscles and Involuntary Muscles.

Figure 13: Muscular Tissue

Striated/ Skeletal/ Voluntary muscles	Smooth/ Unstriated/Involuntary muscles
We can move them according to our own will	We cannot start or stop the movement of involuntary muscles.
They are also called Skeletal Muscles as they are attached to the bones.	They are also called Smooth Muscles.
They are also called Striated Muscles because of the presence of dark and light bands over them	They are also called Unstriated Muscles because they do not have any light or dark bands on them.
The cells of voluntary muscles have more than one nucleus, do not have any branches, and have a long cylindrical structure.	The cells of the involuntary muscles are long and have pointed ends.
For Example, Muscles of our hands and legs.	For Example, The muscles in the alimentary canal and the Iris of our eyes.

Cardiac Muscles
- These are special kinds of involuntary muscles.
- The muscles of the heart are called Cardiac Muscles. They perform rhythmic contraction and relaxation throughout our life.
- They are cylindrical in shape, they have branches and there is a single nucleus.
- Cardiac muscle consists of individual heart muscle cells connected by intercalated discs to work as a single functional organ

4. The Nervous Tissue

How do we react to stimuli?
- This is because of the nervous tissues present in our body. They are capable of transmitting information quickly from the brain to different parts of the body and vice-versa.
Therefore nervous tissues are found in nerves, brain, and spinal cord.
Nervous tissue is made up of cells called the Nerve Cells or Neurons.
These neurons connect together to form the nerves of our body.
Structure of a Neuron
- It is an elongated cell with a Cell Body that consists of some branch-like structure called Dendrites.
- There is a Nucleus present in the centre of the cell body.
- The Nerve Endings of the cell are connected with the cell body via Axon.
- A nerve cell can be up to 1 m long.

Figure 14: Structure of Neuron

The Structure of Neuron

1. Dendrites

They are tree-like extensions (highly-branched) at the beginning of a neuron.
They increase the surface area of the neuron.
They receive chemical signals from different neurons of the body.
They then convert these chemical signals into electrical signals and pass them to the neuron cell body.
A neuron can have a single dendrite or multiple dendrites

2. Cell Body

Also called Soma.
The main function of the cell body and nucleus of the neuron is to maintain the functionality of the cell.
It does not play an active role in the transmission of the signal.
It produces proteins that are required by different parts of the neuron to work properly.
It contains different cell organelles such as mitochondria, Golgi apparatus etc that perform various functions of the cell.

3. Axon

Neurons have one axon in general.
It is a long structure that connects the cell body to the terminals and it also connects with other neurons, cells and organs of the body through nerve terminals.
It allows for the fast transmission of signals. The larger the diameter of the axon the faster it will transmit signals.
It is covered with a special insulating substance called myelin. It helps in the rapid transmission of signals.

4. Schwann Cells

The Myelin sheath that covers the axon is produced by Schwann cells.
The Myelin sheath keeps the signal intact.