Introduction
Life begins from a single cell. This single cell divides repeatedly and forms many cells. In multicellular organisms, these cells do not work randomly. Cells become specialised and form tissues, tissues form organs, organs form organ systems, and organ systems together form the complete organism.
A tissue is a group of similar cells that work together to perform a particular function.
For example:
| Organism | Tissue | Function |
|---|---|---|
| Animals | Muscle tissue | Helps in movement |
| Animals | Nervous tissue | Carries messages and coordinates body activities |
| Plants | Xylem | Transports water and minerals |
| Plants | Phloem | Transports food |
The formation of tissues leads to division of labour, which means different groups of cells perform different functions. This makes the body more efficient.
3.1 Why are Plant and Animal Tissues Different?
Plant and animal tissues are different because plants and animals have different body structures, needs, and ways of living.
Main differences between plant and animal tissues
| Basis | Plant Tissues | Animal Tissues |
|---|---|---|
| Movement | Plants are mostly fixed in one place | Animals generally move from place to place |
| Cell wall | Plant cells have a rigid cell wall | Animal cells do not have a cell wall |
| Support | Plants need strong supporting tissues to remain upright | Animals have bones, muscles, and connective tissues for support and movement |
| Nutrition | Plants prepare food by photosynthesis | Animals obtain food from other sources |
| Growth | Growth occurs in specific regions because of meristematic tissues | Growth usually occurs in most parts during early life |
| Transport | Xylem and phloem transport water, minerals, and food | Blood transports nutrients, gases, hormones, and wastes |
Plant cells have cell walls, so plant tissues are often more rigid. Animal cells do not have cell walls, so they can change shape more easily. This flexibility helps animals in movement.
3.2 Tissues for Growth in Plants
Plants grow in different ways:
- They grow in length.
- They grow in girth or thickness.
- They regrow after cutting or grazing.
This growth happens due to meristematic tissue.
Meristematic Tissue
Meristematic tissue is made up of cells that divide continuously.
Features of meristematic cells
Meristematic cells:
- are small in size,
- have thin cell walls,
- have dense cytoplasm,
- have a large and prominent nucleus,
- have many organelles,
- usually do not have vacuoles,
- are tightly packed with little or no intercellular space.
These features help them divide rapidly and continuously.
3.2.1 Apical Meristem — How do plants grow in length?
Apical meristem is found at the tips of roots and shoots.
Function
It helps plants grow in length.
Example
In the onion root experiment, roots continue to grow if the root tips are present. But when the root tips are cut, root growth stops. This shows that the tip contains actively dividing cells.
Location
| Meristem | Location | Function |
|---|---|---|
| Apical meristem | Root tips and shoot tips | Increases length of roots and shoots |
3.2.2 Lateral Meristem — How do plants grow in girth?
Lateral meristem is found along the sides or circumference of stems.
Function
It increases the girth or thickness of the stem.
In woody plants, lateral meristem forms new cells in concentric layers. This increases the diameter of the stem.
Annual rings
In the cut trunk of a tree, ring-like structures are seen. These are called annual growth rings. They help scientists estimate:
- the age of the tree,
- the growth conditions of different years,
- climatic conditions during growth.
Wide rings show favourable conditions, while narrow rings show unfavourable conditions.
3.2.3 Intercalary Meristem — How do plants grow after being cut?
Intercalary meristem is located at the base of internodes or just above the nodes.
Important terms
| Term | Meaning |
|---|---|
| Node | Point on the stem where leaves or branches arise |
| Internode | Part of the stem between two nodes |
Function
Intercalary meristem helps in regrowth after cutting or grazing.
Example
Grass grows again after being cut or eaten by animals because it has intercalary meristem near the nodes.
Types of Meristematic Tissues
| Type of Meristem | Location | Function |
|---|---|---|
| Apical meristem | Root and shoot tips | Growth in length |
| Lateral meristem | Sides of stem | Growth in girth |
| Intercalary meristem | Base of internodes or above nodes | Regrowth after cutting |
Differentiation
When some meristematic cells lose the ability to divide, they become specialised to perform specific functions. This process is called differentiation.
Through differentiation, meristematic tissue changes into permanent tissue.
3.2.4 Permanent Tissues
Permanent tissues are formed from meristematic tissues. Their cells have lost the ability to divide and are specialised for particular functions.
Permanent tissues are of two main types:
- Simple permanent tissues
- Complex permanent tissues
| Type | Meaning | Examples |
|---|---|---|
| Simple permanent tissue | Made of one type of cell | Parenchyma, collenchyma, sclerenchyma |
| Complex permanent tissue | Made of more than one type of cell | Xylem, phloem |
(i) Protective Tissue — Epidermis
The epidermis is the outermost layer of the plant body.
Structure
- It is usually a single layer of tightly packed cells.
- Cells are flat and rectangular.
- It may be covered by a waxy layer called cuticle.
Functions of epidermis
The epidermis:
- protects the plant from mechanical injury,
- prevents entry of harmful microorganisms,
- reduces water loss,
- protects against parasites,
- helps in absorption through root hairs,
- helps in gaseous exchange through stomata.
Cuticle
The cuticle is a waxy layer made of cutin. It reduces water loss. It is thick in desert plants because they need to conserve water.
Root hairs
Root hairs are hair-like projections from epidermal cells of roots. They increase the surface area for absorption of water and minerals.
Stomata
Stomata are small pores present in the epidermis of leaves. They help in:
- gaseous exchange,
- transpiration,
- elimination of some wastes.
Transpiration is the loss of water vapour through stomata. It helps create a transpiration pull, which helps water move upward through xylem.
(ii) Supporting Tissue — Simple Permanent Tissues
Supporting tissues help plants stay upright, flexible, strong, and protected.
There are three types of simple permanent tissues:
- Parenchyma
- Collenchyma
- Sclerenchyma
a. Parenchyma
Parenchyma is made up of living cells with thin cell walls.
Structure
- Cells are living.
- Cell walls are thin.
- Cells are loosely packed.
- Intercellular spaces are present.
Functions
Parenchyma:
- stores food,
- performs photosynthesis in green parts,
- helps aquatic plants float when it forms air spaces.
In aquatic plants, parenchyma with air spaces is called aerenchyma.
b. Collenchyma
Collenchyma is made up of living cells with unevenly thickened corners.
Structure
- Cells are living.
- Corners are thickened due to pectin deposition.
- Cells provide flexibility.
Functions
Collenchyma:
- provides support,
- gives flexibility,
- allows plant parts to bend without breaking.
Example
Young stems and tendrils bend without breaking because of collenchyma.
c. Sclerenchyma
Sclerenchyma cells have thick, hard walls due to lignin deposition.
Structure
- Cells have thick lignified walls.
- Most cells are dead.
- Cells are hard and strong.
Functions
Sclerenchyma:
- provides strength,
- forms woody parts,
- gives hardness to seed coats and nut shells.
Examples
Sclerenchyma is found in:
- stems,
- leaf veins,
- coconut husk,
- walnut shell,
- hard seed coats.
Difference between Parenchyma, Collenchyma and Sclerenchyma
| Feature | Parenchyma | Collenchyma | Sclerenchyma |
|---|---|---|---|
| Nature of cells | Living | Living | Mostly dead |
| Cell wall | Thin | Unevenly thickened at corners | Very thick and lignified |
| Intercellular space | Present | Less | Absent |
| Main function | Storage, photosynthesis, floating | Support and flexibility | Strength and hardness |
| Example | Soft parts of plants | Young stems, tendrils | Coconut husk, walnut shell |
(iii) Conducting Tissues — Complex Permanent Tissues
Plants need tissues to transport water, minerals, and food. These tissues are called conducting tissues.
There are two main conducting tissues:
- Xylem
- Phloem
Together, xylem and phloem form the vascular tissue system.
Xylem
Xylem transports water and minerals from roots to other parts of the plant.
Components of xylem
Xylem consists of:
- tracheids,
- vessels,
- xylem parenchyma,
- xylem fibres.
Nature of xylem cells
Most xylem cells are dead, except xylem parenchyma, which is living.
Functions of xylem
Xylem:
- transports water,
- transports minerals,
- provides mechanical strength.
Phloem
Phloem transports food prepared in leaves to other parts of the plant.
Components of phloem
Phloem consists of:
- sieve tubes,
- companion cells,
- phloem parenchyma,
- phloem fibres.
Nature of phloem cells
Phloem is mostly made up of living cells.
Functions of phloem
Phloem:
- transports food,
- stores food materials, resins, tannins, and latex,
- provides support through phloem fibres.
Companion cells
Companion cells help sieve tubes in loading and unloading sugars.
Difference between Xylem and Phloem
| Feature | Xylem | Phloem |
|---|---|---|
| Main function | Transports water and minerals | Transports food |
| Direction of transport | Mainly upward | Both upward and downward |
| Nature of cells | Mostly dead | Mostly living |
| Components | Tracheids, vessels, xylem parenchyma, xylem fibres | Sieve tubes, companion cells, phloem parenchyma, phloem fibres |
| Additional function | Gives strength | Stores food and other materials |
Tissue Systems in Plants
Plant tissues are organised into three tissue systems:
| Tissue System | Main Components | Function |
|---|---|---|
| Dermal tissue system | Epidermis | Protection and reduction of water loss |
| Ground tissue system | Parenchyma, collenchyma, sclerenchyma | Storage, support, photosynthesis |
| Vascular tissue system | Xylem and phloem | Transport of water, minerals, and food |
3.3 Animal Tissues
Animal tissues are groups of specialised cells that perform different functions in the animal body.
The four main types of animal tissues are:
- Epithelial tissue
- Connective tissue
- Muscular tissue
- Nervous tissue
3.3.1 Epithelial Tissues — Structure and Functions
Epithelial tissue forms the outer covering of the body and lines internal organs.
Locations
Epithelial tissue is found in:
- skin,
- mouth,
- lungs,
- blood vessels,
- intestine,
- stomach lining,
- glands.
Structure
- Cells are closely packed.
- Very little intercellular space is present.
- It forms protective coverings and linings.
Functions
Epithelial tissue helps in:
- protection,
- absorption,
- secretion,
- exchange of gases and liquids,
- sensory functions,
- movement of substances.
Types of Epithelial Tissue Based on Function
| Function | Structure | Location |
|---|---|---|
| Exchange | Single layer of thin, flat cells | Blood vessels and lungs |
| Protection | Many layers of tightly packed cells | Skin, mouth, oesophagus |
| Secretion | Cuboidal or columnar cells specialised for secretion | Salivary glands, sweat glands, stomach lining |
| Sensory function | Receptor cells with cilia | Nostrils, taste buds, inner ear |
| Absorption | Tall pillar-like cells | Small intestine |
3.3.2 How are various parts connected in our body?
The tissue that connects and supports other tissues is called connective tissue.
Examples of connective tissue:
- blood,
- bone,
- cartilage,
- tendon,
- ligament.
Connective tissues differ because of differences in their matrix.
The matrix may be:
- fluid,
- jelly-like,
- hard,
- rigid.
Blood as Connective Tissue
Blood is a fluid connective tissue. It connects different parts of the body by transporting materials.
Components of blood
Blood contains:
- plasma,
- red blood cells,
- white blood cells,
- platelets.
Functions of blood components
| Component | Function |
|---|---|
| Plasma | Transports nutrients, hormones, gases, and wastes |
| RBCs | Carry oxygen because they contain haemoglobin |
| WBCs | Fight infection |
| Platelets | Help in blood clotting |
The red colour of blood is due to haemoglobin, an iron-rich protein present in RBCs.
Bone
Bone is a hard connective tissue.
Function
Bones:
- provide support,
- give shape to the body,
- protect internal organs,
- help in movement with muscles.
The matrix of bone contains calcium and phosphorus compounds, which make it hard and strong.
Cartilage
Cartilage is a flexible connective tissue.
Function
Cartilage:
- provides flexibility,
- cushions the ends of bones,
- absorbs shock.
Examples
Cartilage is found in:
- ear,
- nose,
- joints,
- between vertebrae.
Tendon
Tendon connects muscle to bone.
Function
It transmits the force of muscle contraction to bones and helps in movement.
Ligament
Ligament connects bone to bone.
Function
It:
- provides stability to joints,
- limits excessive movement,
- prevents dislocation.
Difference between Tendon and Ligament
| Feature | Tendon | Ligament |
|---|---|---|
| Connects | Muscle to bone | Bone to bone |
| Function | Helps in movement | Stabilises joints |
| Nature | Strong and flexible | Strong and elastic |
3.3.3 Can we control movement in our body?
Movement in our body happens due to muscular tissue.
There are two types of movements:
- Voluntary movements
- Involuntary movements
Voluntary movements
Movements that are under our conscious control are called voluntary movements.
Examples:
- running,
- writing,
- lifting objects,
- walking.
These movements are performed by skeletal muscles.
Involuntary movements
Movements that occur automatically without conscious control are called involuntary movements.
Examples:
- movement of food in the intestine,
- heartbeat,
- movement of internal organs.
These movements are performed by smooth muscles and cardiac muscles.
Types of Muscles
1. Skeletal Muscle
Skeletal muscles are attached to bones.
Features
- Cells are long and cylindrical.
- Cells are unbranched.
- Cells are multinucleate.
- They have light and dark bands, so they are striated.
- They are voluntary.
Function
They help in body movement.
2. Smooth Muscle
Smooth muscles are found in internal organs like the stomach and intestine.
Features
- Cells are spindle-shaped.
- Each cell has one nucleus.
- No striations are present.
- They are involuntary.
Function
They help in slow and continuous movements, such as movement of food in the digestive tract.
3. Cardiac Muscle
Cardiac muscles are found only in the heart.
Features
- Cells are cylindrical and branched.
- Each cell has one nucleus.
- They have faint striations.
- They are involuntary.
- They work rhythmically without fatigue.
Function
They help the heart beat throughout life.
Difference between Skeletal, Smooth and Cardiac Muscles
| Feature | Skeletal Muscle | Smooth Muscle | Cardiac Muscle |
|---|---|---|---|
| Location | Attached to bones | Stomach, intestine, internal organs | Heart |
| Shape | Long, cylindrical | Spindle-shaped | Cylindrical and branched |
| Nucleus | Many nuclei | One nucleus | One nucleus |
| Striations | Present | Absent | Faintly present |
| Control | Voluntary | Involuntary | Involuntary |
| Function | Body movement | Movement in internal organs | Heartbeat |
3.3.4 How does the body sense, communicate and respond?
The body senses, communicates, and responds through nervous tissue.
Nervous tissue forms the control and coordination network of the body.
Main functions of nervous tissue
Nervous tissue:
- receives messages,
- processes information,
- sends signals to different body parts,
- controls muscles,
- helps in memory,
- coordinates responses.
The brain acts as the control centre of the body.
Neuron
The cells of nervous tissue are called neurons or nerve cells.
Parts of a neuron
A neuron has three main parts:
- Cell body
- Dendrites
- Axon
| Part | Function |
|---|---|
| Cell body | Contains nucleus and controls cell activities |
| Dendrites | Receive signals from other neurons |
| Axon | Carries messages away from the cell body |
| Axon terminals | Pass messages to other cells |
3.4 The Musculoskeletal System
The musculoskeletal system is made up of:
- bones,
- muscles,
- joints,
- cartilage,
- tendons,
- ligaments.
Functions of musculoskeletal system
It helps us to:
- stand upright,
- move,
- maintain posture,
- protect delicate organs.
The musculoskeletal system works under the control of the nervous system.
How movement occurs
- The brain sends signals through nervous tissue.
- Muscles receive the signal.
- Muscles contract.
- Tendons transmit the force to bones.
- Bones move at joints.
Muscles pull bones to produce movement.
3.4.1 The Musculoskeletal System in Action
Different body parts move in different ways because they have different types of joints.
A joint is a place where two or more bones meet.
Joints allow movement, but they do not move bones by themselves. Movement happens when muscles pull bones.
Examples:
| Body Part | Type of Movement |
|---|---|
| Shoulder | Movement in many directions |
| Elbow | Bending and straightening |
| Knee | Bending and straightening |
| Neck | Turning and partial rotation |
| Fingers | Bending |
| Wrist | Bending, turning, side movement |
3.5 Types of Joints
There are different types of joints in the human body.
3.5.1 Ball and Socket Joint
In a ball and socket joint, the rounded end of one bone fits into a hollow part of another bone.
Movement allowed
It allows movement in many directions:
- forward,
- backward,
- sideways,
- circular movement.
Example
Shoulder joint and hip joint.
3.5.2 Hinge Joint
A hinge joint allows movement in one direction, like a door hinge.
Movement allowed
It allows bending and straightening.
Examples
- Elbow joint
- Knee joint
- Ankle joint
3.5.3 Pivot Joint
A pivot joint allows rotation.
Example
The joint between skull and backbone allows us to move the head side to side, like saying “no”.
3.5.4 Fixed Joints
Fixed joints do not allow movement.
Example
The bones of the skull are joined by fixed joints. This protects the brain, eyes, and ears.
Types of Joints at a Glance
| Joint | Movement | Example |
|---|---|---|
| Ball and socket joint | Movement in many directions | Shoulder, hip |
| Hinge joint | Movement in one direction | Elbow, knee |
| Pivot joint | Side-to-side rotation | Neck |
| Fixed joint | No movement | Skull bones |
3.6 Skeletal System
The skeletal system is the framework of bones in the body.
Functions of skeletal system
The skeletal system:
- gives shape to the body,
- provides support,
- protects delicate organs,
- helps in movement,
- supports muscles.
Main Parts of the Skeletal System
1. Skull
The skull protects the brain, eyes, and ears. The bones of the skull are joined by fixed joints.
2. Vertebral Column
The vertebral column is also called the backbone or spine.
It is made up of many small bones called vertebrae.
Functions
The vertebral column:
- supports the body,
- helps us stand upright,
- protects the spinal cord,
- allows bending and twisting.
Between vertebrae, cartilage discs act as cushions and provide flexibility.
3. Rib Cage
Humans have 12 pairs of ribs. Together, they form the rib cage.
Functions
The rib cage:
- protects the heart,
- protects the lungs,
- helps in breathing.
The ribs are attached to the spine at the back and to the breastbone or sternum in the front. Flexible cartilage allows the rib cage to expand and contract during breathing.
Health of Bones and Muscles
To keep the musculoskeletal system healthy, we should maintain:
- correct posture,
- proper nutrition,
- regular exercise,
- yoga,
- physical activity.
Yoga improves flexibility, posture, breathing, and reduces stress.
Think as a Scientist — From One Cell to an Organism: Totipotency
In 1958, F. C. Steward showed that single cells from the phloem of carrot could develop into a complete carrot plant under suitable laboratory conditions.
What happened in the experiment?
- Phloem cells from carrot were taken.
- These cells were grown in a nutrient medium containing sugars and hormones.
- The cells divided to form a mass of cells.
- These cells differentiated into roots and shoots.
- A complete plant developed.
Important terms
Dedifferentiation
When specialised cells regain the ability to divide, it is called dedifferentiation.
Redifferentiation
When these dividing cells again become specialised to form different tissues and organs, it is called redifferentiation.
Totipotency
The ability of a single plant cell to divide and develop into a complete plant is called totipotency.
Such cells are called totipotent cells.
Importance of Totipotency
Totipotency is useful in:
- plant tissue culture,
- production of disease-free plants,
- crop improvement,
- genetic engineering,
- production of valuable plant chemicals.
Crown Gall Disease and Science
Crown gall disease is caused by a bacterium called Agrobacterium tumefaciens.
In this disease, tumour-like swellings develop on plant stems due to uncontrolled cell division.
Scientists studied how this bacterium transfers genetic material into plant cells. This knowledge is now used in genetic engineering to introduce useful genes into plants.
Important Keywords
| Keyword | Meaning |
|---|---|
| Tissue | Group of similar cells performing a specific function |
| Division of labour | Different cells or tissues performing different functions |
| Meristematic tissue | Tissue made of actively dividing cells |
| Permanent tissue | Tissue formed after differentiation; cells usually do not divide |
| Differentiation | Process by which cells become specialised |
| Epidermis | Outermost protective layer of plant body |
| Cuticle | Waxy layer on epidermis that reduces water loss |
| Stomata | Pores in leaves for gaseous exchange and transpiration |
| Xylem | Tissue that transports water and minerals |
| Phloem | Tissue that transports food |
| Epithelial tissue | Tissue that covers body surfaces and lines organs |
| Connective tissue | Tissue that connects and supports body parts |
| Muscular tissue | Tissue that helps in movement |
| Nervous tissue | Tissue that receives and transmits messages |
| Neuron | Nerve cell |
| Tendon | Connects muscle to bone |
| Ligament | Connects bone to bone |
| Joint | Place where two or more bones meet |
| Totipotency | Ability of a single cell to develop into a complete organism |
Quick Revision Tables
Plant Tissues
| Category | Tissue | Function |
|---|---|---|
| Meristematic tissue | Apical meristem | Growth in length |
| Meristematic tissue | Lateral meristem | Growth in girth |
| Meristematic tissue | Intercalary meristem | Regrowth after cutting |
| Simple permanent tissue | Parenchyma | Storage, photosynthesis, floating |
| Simple permanent tissue | Collenchyma | Support and flexibility |
| Simple permanent tissue | Sclerenchyma | Strength and hardness |
| Complex permanent tissue | Xylem | Transport of water and minerals |
| Complex permanent tissue | Phloem | Transport of food |
Animal Tissues
| Tissue | Main Function | Examples/Location |
|---|---|---|
| Epithelial tissue | Protection, absorption, secretion, exchange | Skin, intestine, lungs |
| Connective tissue | Connects and supports body parts | Blood, bone, cartilage, tendon, ligament |
| Muscular tissue | Movement | Skeletal muscles, smooth muscles, cardiac muscles |
| Nervous tissue | Control and coordination | Brain, spinal cord, nerves |
Summary of the Chapter
In this chapter, we learn that tissues are groups of similar cells that work together to perform specific functions. In multicellular organisms, tissues help in division of labour and increase efficiency.
Plant and animal tissues are different because plants are mostly fixed, have cell walls, prepare their own food, and grow throughout life in specific regions. Animals usually move, do not have cell walls, and have tissues specialised for digestion, movement, support, and coordination.
Plant growth occurs due to meristematic tissues. Apical meristem increases length, lateral meristem increases girth, and intercalary meristem helps in regrowth after cutting or grazing. When meristematic cells become specialised, they form permanent tissues. Permanent tissues may be simple or complex. Simple permanent tissues include parenchyma, collenchyma, and sclerenchyma. Complex permanent tissues include xylem and phloem. Xylem transports water and minerals, while phloem transports food.
Animal tissues are mainly of four types: epithelial, connective, muscular, and nervous. Epithelial tissue protects body surfaces and lines internal organs. Connective tissue connects and supports body parts. Blood, bone, cartilage, tendons, and ligaments are examples of connective tissues. Muscular tissue helps in movement. Skeletal muscles control voluntary movements, while smooth and cardiac muscles control involuntary movements. Nervous tissue contains neurons that receive and transmit messages.
The musculoskeletal system consists of bones, muscles, joints, cartilage, tendons, and ligaments. It helps in movement, posture, and protection of organs. Different types of joints allow different movements. Ball and socket joints allow movement in many directions, hinge joints allow bending and straightening, pivot joints allow rotation, and fixed joints do not allow movement.
The chapter also explains totipotency, the ability of a single plant cell to develop into a complete plant under suitable conditions. This idea is important in plant tissue culture, crop improvement, and genetic engineering.
