Tissues class 9 Notes

Introduction

A tissue is a group of similar cells that work together to perform a specific function.
In multicellular organisms, cells are organized in the following way:

Cells → Tissues → Organs → Organ System → Organism

Why Do We Need Tissues?

In unicellular organisms, one cell performs all functions.
But in multicellular organisms:

           1) Different cells perform different functions
           2) Division of labour increases efficiency
           3) Body functions properly and systematically

This concept is called division of labour.

Are Plants and Animals Made of Same Types of Tissues?

No, plants and animals are not made of the same types of tissues.
Although both are multicellular and made of cells, their tissues are different in structure and function.

Why Are Plant and Animal Tissues Different?

Plants and animals have different ways of living.

Plants are fixed in one place (non-motile) and make their own food.
Animals move from place to place and depend on others for food.

- So their tissues are designed according to their needs.

Plants Tissues

1) Meristematic Tissue

Meristematic tissue is a special type of plant tissue responsible for growth.
It is found in the growing regions of plants like root tips and shoot tips.
Meristematic tissue consists of actively dividing cells.
These cells continuously divide to increase the length and thickness of plants.
Because of this tissue, plants grow throughout their life.

Characteristics of Meristematic Tissue

Cells are small and actively dividing.
Cell wall is thin.
Cells have dense cytoplasm.
Large nucleus is present.
Vacuoles are absent or very small.
Cells are closely packed (no intercellular spaces).

Types of Meristematic Tissue

Meristematic tissues are classified based on their position in the plant.

1) Apical Meristem

Location: Tips of roots and shoots
Function:

1) Increases the length of the plant

2) Responsible for primary growth

Example: Root tip and shoot tip

2) Intercalary Meristem

Location: At the base of leaves or internodes (near nodes)
Function:

1) Helps in growth of internodes

2) Seen mostly in grasses

Example: Grass plants regrow quickly after cutting because of intercalary meristem.

3) Lateral Meristem

Location: Along the sides of stems and roots
Function:

1) Increases the girth (thickness) of the plant

2) Responsible for secondary growth

Example: Cork cambium and vascular cambium

2) Permanent Tissue

Permanent tissue is a type of plant tissue formed from meristematic tissue.
When meristematic cells stop dividing and become specialized to perform specific functions, they form permanent tissue.
Permanent tissue consists of mature cells that:

1) Have lost the power of division

2) Perform specific functions like support, storage, and transport

Characteristics of Permanent Tissue

Cells do not divide.
Cells are larger than meristematic cells.
Vacuoles are large.
Cell walls may be thin or thick.
Intercellular spaces may be present.
Cells are specialized for particular functions.

Types of Permanent Tissue

Permanent tissues are of two main types:

1) Simple Permanent Tissue

Made up of only one type of cell.

(a) Parenchyma

Found in: soft parts of plant (leaves, fruits, stem)
Functions:

1) Storage of food

2) Photosynthesis (when chlorophyll present → called chlorenchyma)

3) Provides support

Cells are:

1) Thin-walled

2) Living

3) Have intercellular spaces

(b) Collenchyma

Found in: Leaf stalks, below epidermis of stem
Functions:

1) Provides support and flexibility

Cells are:

1) Living

2) Unevenly thickened at corners

3) Help plant parts bend without breaking

(c) Sclerenchyma

Found in: Hard parts like coconut husk
Functions:

1) Provides strength and hardness

Cells are:

1) Dead

2) Thick lignified walls

3) No internal space

Example: Husk of coconut is very hard due to sclerenchyma.

2) Complex Permanent Tissue

Made up of more than one type of cell working together.

(a) Xylem

Function:

1) Transports water and minerals from roots to other parts

Parts of xylem:

1) Tracheids

2) Vessels

3) Xylem parenchyma

4) Xylem fibres

(b) Phloem

Function:

1) Transports food from leaves to other parts

Parts of phloem:

1) Sieve tubes

2) Companion cells

3) Phloem parenchyma

4) Phloem fibres

Animal Tissue

In animals, tissues are mainly divided into four types:

1) Epithelial Tissue

2) Connective Tissue

3) Muscular Tissue

4) Nervous Tissue

1) Epithelial Tissue:

Epithelial tissue is the protective covering tissue of the body. It covers the outer surface of the body and lines the internal organs and cavities.
It forms the skin, lines the mouth, stomach, lungs, blood vessels, etc.

Definition

Epithelial tissue is a group of closely packed cells that form a continuous sheet to protect and support the body.

Characteristics of Epithelial Tissue

1) Cells are tightly packed

2) Very little intercellular space

3) Forms a continuous layer

4) Rests on a thin layer called basement membrane

5) Does not have blood vessels (Non-vascular)

6) Cells can regenerate quickly

Functions of Epithelial Tissue

Protection (Skin protects internal organs)
Absorption (Small intestine absorbs nutrients)
Secretion (Glands secrete enzymes, hormones)
Excretion (Kidney tubules remove waste)
Exchange of gases (Lungs)

Types of Epithelial Tissue

1) Squamous Epithelium

Structure:

Thin, flat cells
Arranged like tiles on a floor

Function:

Allows diffusion and filtration

Location:

Air sacs (alveoli) of lungs
Blood vessels

2) Cuboidal Epithelium

Structure:

Cube-shaped cells
Central nucleus

Function:

Secretion and absorption

Location:

Kidney tubules
Salivary glands

3) Columnar Epithelium

Structure:

Tall and pillar-like cells

Function:

Absorption
Secretion

Location:

Lining of stomach and intestine

4) Ciliated Epithelium

Structure:

Has hair-like projections called cilia

Function:

Moves substances
Pushes mucus forward

Location:

Respiratory tract
Oviduct (fallopian tube)

5) Glandular Epithelium

Structure:

Specialized epithelial cells

Function:

Secretion of hormones, enzymes, sweat

Location:

Endocrine glands (Hormones into blood)
Exocrine glands (Secretion through ducts)

2) Connective Tissue

Connective tissue is the tissue that connects, supports, binds, or separates different organs and tissues in the body.
Unlike epithelial tissue, the cells in connective tissue are loosely packed and embedded in a matrix (a material between cells).

Definition

Connective tissue is a group of cells that are loosely arranged in an intercellular matrix and help in support, transport, and protection of the body.

Characteristics of Connective Tissue

1) Cells are loosely packed

2) Large intercellular space

3) Matrix (can be solid, liquid, or semi-solid) is present

4) Usually has blood supply (except cartilage)

Functions of Connective Tissue

Connects tissues and organs
Provides support and shape
Stores fat
Transports substances
Protects internal organs

Types of Connective Tissue

Connective tissue is mainly divided into three groups:

1) Loose Connective Tissue

(a) Areolar Tissue

Structure:

Loose arrangement of cells and fibers

Function:

Fills spaces inside organs
Supports internal organs
Helps in tissue repair

Location:

Between skin and muscles
Around blood vessels and nerves

(b) Adipose Tissue

Structure:

Cells filled with fat

Function:

Stores fat
Provides insulation
Protects organs

Location:

Under the skin
Around kidneys

2) Supporting Connective Tissue

(a) Cartilage

Structure:

Firm but flexible

Function:

Provides flexibility
Reduces friction in joints

Location:

Nose
Ear
Trachea
Ends of bones

(b) Bone

Structure:

Hard and strong
Contains minerals like calcium and phosphorus

Function:

Forms skeleton
Protects organs
Makes blood cells (in bone marrow)

Location:

All bones of the body

3) Fluid Connective Tissue

(a) Blood

Structure:

Liquid matrix called plasma
Contains:
- RBCs (Red Blood Cells)
- WBCs (White Blood Cells)
- Platelets

Function:

Transports oxygen, nutrients, hormones
Fights infections
Helps in clotting

(b) Lymph

Function:

Transports fats
Helps in immunity

3) Muscular Tissue

Muscular tissue is the tissue responsible for movement in our body. It helps in moving body parts, walking, talking, breathing, and even pumping blood.
Muscles work by contracting (shortening) and relaxing.

Definition

Muscular tissue is a group of muscle cells (muscle fibers) that can contract and relax to produce movement.

Characteristics of Muscular Tissue

1) Cells are long and cylindrical

2) Called muscle fibers

3) Have the ability to contract and relax

4) Contain special proteins (actin and myosin)

5) Well supplied with blood

Functions of Muscular Tissue

Helps in body movement
Maintains posture
Circulates blood
Movement of food in stomach and intestine
Helps in breathing

Types of Muscular Tissue (Very Important)

There are three types of muscular tissue:

1) Striated Muscle (Skeletal Muscle)

Structure:

Long and cylindrical
Multinucleated (many nuclei)
Shows light and dark bands (stripes) → called striations

Function:

Responsible for voluntary movements

Control:

Voluntary (we control it)

Location:

Attached to bones (arms, legs)

Example:

Biceps, triceps

2) Smooth Muscle

Structure:

Spindle-shaped cells
Single nucleus
No stripes

Function:

Moves food in digestive tract
Controls internal movements

Control:

Involuntary (not under our control)

Location:

Stomach
Intestine
Blood vessels

3) Cardiac Muscle

Structure:

Cylindrical and branched
Has striations
Single nucleus
Special junctions (intercalated discs)

Function:

Pumps blood continuously

Control:

Involuntary

Location:

Found only in the heart

4) Nervous Tissue

Nervous tissue is the tissue that controls and coordinates all activities of the body. It receives information (stimulus), processes it, and sends instructions (response).
It helps us to think, feel, react, and remember.

Definition

Nervous tissue is a specialized tissue made of nerve cells (neurons) that carry messages in the form of electrical impulses from one part of the body to another.

Location of Nervous Tissue

Brain
Spinal cord
Nerves throughout the body

These together form the nervous system.

Structure of a Neuron (Nerve Cell)

The basic unit of nervous tissue is the neuron.
A neuron has three main parts:

1) Cell Body (Cyton)

Contains nucleus
Controls activities of the cell

2) Dendrites

Short, branched extensions
Receive signals from other cells

3) Axon

Long extension
Transmits impulses away from cell body

Message flows:
Dendrites → Cell Body → Axon

Characteristics of Nervous Tissue

1) Cells are long and branched

2) Can transmit electrical impulses

3) Communication is very fast

4) Limited ability to regenerate

Functions of Nervous Tissue

Controls body movements
Coordinates body organs
Helps in thinking and memory
Detects pain, heat, cold, touch
Controls reflex actions

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