Chapter 3: Tissues in Action
1. Tissue — Meaning and Importance
- A tissue is a group of cells that work together to perform a particular function.
- In multicellular organisms, organisation occurs as:
Cells → Tissues → Organs → Organ systems → Organism
- Division of labour among tissues makes the body more efficient and allows complex life processes.
Plants vs Animals
- Plants are generally fixed in one place, so they need strong supporting tissues.
- Plant cells have a cell wall, which provides rigidity.
- Animals need greater flexibility for movement.
- Plants make food by photosynthesis, while animals obtain and digest food.
- Growth patterns also differ because the tissues responsible for growth are different.
2. Plant Tissues
Plant tissues are broadly divided into:
- Meristematic tissues — actively dividing
- Permanent tissues — specialised and generally no longer dividing
Meristematic Tissue
Meristematic cells:
- Divide continuously.
- Are small and closely packed.
- Have thin cell walls.
- Have dense cytoplasm and a prominent nucleus.
- Usually have little or no vacuole.
- Produce new cells for plant growth.
Types of Meristems
| Type | Location | Main function |
|---|---|---|
| Apical meristem | Root and shoot tips | Increases length |
| Lateral meristem | Along the circumference of stems | Increases girth |
| Intercalary meristem | Near nodes/base of internodes in certain plants | Helps regeneration after cutting |
Easy Memory Trick
A-L-I = Along Length, Increase girth, Intercalary regeneration
- Apical → Length
- Lateral → Girth
- Intercalary → Regrowth
Differentiation
Meristematic cells that stop dividing undergo structural and functional changes and become specialised permanent cells.
This process is called differentiation.
3. Permanent Tissues
Permanent tissues are specialised tissues formed from meristematic cells.
They may be:
- Simple permanent tissues — mainly one type of cell
- Complex permanent tissues — more than one type of cell working together
A. Protective Tissue — Epidermis
- Epidermis forms the outermost covering of the plant.
- Protects against mechanical injury, microorganisms and excessive water loss.
- It is generally a tightly packed single layer of cells.
- It may have a waxy cuticle.
- In roots, epidermal cells form root hairs, which increase the surface area for absorption.
- Leaves contain stomata for gaseous exchange and transpiration.
- Transpiration contributes to the upward movement of water through transpiration pull.
Important terms
Root hair → absorption of water and minerals
Stomata → gaseous exchange + transpiration
Cuticle → protection + reduced water loss
4. Simple Permanent Tissues
There are three major types:
Parenchyma
- Living cells
- Thin cell walls
- Usually loosely packed with intercellular spaces
- Mainly stores food
- Can perform photosynthesis in green parts
- In aquatic plants, air spaces help the plant float
Key word: Storage
Collenchyma
- Living cells
- Corners have unevenly thickened walls.
- Provides support and flexibility.
- Allows plant parts such as stems and tendrils to bend without breaking.
Key word: Flexibility
Sclerenchyma
- Cells have thick walls due to lignin.
- Most cells are dead.
- Provides hardness, strength and mechanical support.
- Found in structures such as stems, leaf veins, coconut husk and hard seed coverings.
Key word: Strength
Quick Comparison
| Tissue | Main feature | Main function |
|---|---|---|
| Parenchyma | Thin-walled, living | Storage/photosynthesis |
| Collenchyma | Unevenly thickened corners | Flexibility + support |
| Sclerenchyma | Thick, lignified walls | Strength + rigidity |
5. Complex Permanent Tissues
The two major conducting tissues are:
Xylem
Function: Transports water and minerals from roots to other parts of the plant.
It also provides mechanical strength.
Components:
- Tracheids
- Vessels
- Xylem parenchyma
- Xylem fibres
Important: Xylem parenchyma is the living component; tracheids, vessels and fibres are primarily sclerenchymatous.
Phloem
Function: Transports food from leaves to other parts of the plant.
Components:
- Sieve tubes
- Companion cells
- Phloem parenchyma
- Phloem fibres
Companion cells help regulate loading and unloading of sugars in sieve tubes.
Easy Difference
Xylem → Water + minerals
Phloem → Food
6. Plant Tissue Systems
Three major tissue systems are:
1. Dermal tissue system
- Forms the outer covering.
- Protects internal parts.
- Reduces water loss.
2. Ground tissue system
- Forms much of the plant body between dermal and conducting tissues.
- Includes parenchyma, collenchyma and sclerenchyma.
3. Vascular tissue system
- Made of xylem and phloem.
- Responsible mainly for conduction.
7. Animal Tissues
Four major types:
- Epithelial
- Connective
- Muscular
- Nervous
8. Epithelial Tissue
- Forms the outer covering of the body.
- Also lines internal organs such as the mouth, lungs, blood vessels and intestine.
- Cells are closely packed with very little space between them.
- Provides protection and performs functions such as exchange, secretion and absorption.
Major forms/functions
| Function | Important feature | Example/location |
|---|---|---|
| Exchange | Thin, flat single layer | Lungs, blood vessels |
| Protection | Many layers | Skin, mouth, oesophagus |
| Secretion | Specialised secretory cells | Glands, stomach lining |
| Sensory function | Receptor cells | Nostrils, taste buds, inner ear |
| Absorption | Tall cells, often with hair-like structures | Small intestine |
Exam point: Thin epithelial layers allow rapid exchange of gases and substances.
9. Connective Tissue
Connective tissue connects and supports different tissues and body parts.
Examples:
- Blood
- Bone
- Cartilage
- Tendons
- Ligaments
Blood
- A fluid connective tissue.
- Its matrix is watery.
- RBCs: contain haemoglobin, giving blood its red colour.
- Platelets: help in blood clotting.
- WBCs: participate in defence and accumulate at sites of infection.
Bone
- Has a hard, rigid matrix containing calcium and phosphorus compounds.
- Provides strength, support and protection.
Cartilage
- Has a softer, flexible matrix.
- Provides flexibility and cushions the ends of bones.
Tendon
- Connects muscle to bone.
- Transmits muscular force to bones and helps produce movement.
Ligament
- Connects bone to bone.
- Provides stability and limits excessive movement.
Very Important Difference
Tendon = Muscle → Bone
Ligament = Bone → Bone
10. Muscular Tissue
Muscles produce movement.
Skeletal Muscle
- Responsible for voluntary movements.
- Attached to the skeleton.
- Fibres are long, cylindrical, unbranched, multinucleate and striated.
Example: Running, writing, lifting an object.
Smooth Muscle
- Responsible for involuntary movements.
- Found in organs such as the stomach and intestines.
- Cells are spindle-shaped.
- Have one nucleus.
- Lack striations.
- Help in slow, continuous movements such as digestion.
Cardiac Muscle
- Found only in the heart.
- Works continuously and rhythmically.
- Fibres are branched and have a single nucleus.
- Have faint striations.
- Enables continuous beating of the heart.
Quick Comparison
| Muscle | Control | Location | Appearance |
|---|---|---|---|
| Skeletal | Voluntary | Attached to skeleton | Striated |
| Smooth | Involuntary | Internal organs | Non-striated |
| Cardiac | Involuntary | Heart | Branched, faintly striated |
11. Nervous Tissue
- Nervous tissue controls coordination and communication in the body.
- Its specialised cells are called neurons.
- Neurons receive, process and transmit messages.
Main parts of a neuron
- Cell body: contains nucleus and controls cell activities.
- Dendrites: receive signals.
- Axon: carries messages away from the cell body.
- Axon terminals: transmit messages to other cells.
Key idea:
Dendrites receive → Axon carries → Axon terminals transmit
12. Musculoskeletal System
The musculoskeletal system includes:
Bones + Muscles + Joints + Cartilage + Tendons + Ligaments
Functions:
- Maintains posture.
- Supports the body.
- Produces movement.
- Protects delicate organs.
Muscles are attached to bones through tendons. When a muscle contracts, the tendon transfers the force to the bone, causing movement at a joint.
13. Joints
A joint is a junction between two or more bones.
Ball-and-socket joint
- Allows movement in many directions.
- Example: shoulder.
Hinge joint
- Mainly allows bending and straightening in one direction.
- Examples: elbow and knee.
Pivot joint
- Allows rotation around an axis.
- Example: joint between the skull and backbone, allowing side-to-side head movement.
Fixed joint
- Does not permit movement.
- Example: joints between skull bones.
- Helps protect the brain.
Memory Trick
Ball → Many directions
Hinge → One main direction
Pivot → Rotation
Fixed → No movement
14. Skeletal System
The skeletal system:
- Provides a framework for the body.
- Gives strength and support.
- Protects internal organs.
- Helps maintain posture.
Major structures include:
- Skull
- Vertebral column
- Rib cage
Vertebral column
- Made of small bones called vertebrae.
- Supports the body.
- Cartilage discs between vertebrae provide cushioning and flexibility.
Rib cage
- Contains 12 pairs of ribs.
- Protects important organs such as the heart and lungs.
- Its flexible connections allow expansion and contraction during breathing.
15. Totipotency
Totipotency is the ability of certain mature plant cells, under suitable conditions, to regain the ability to divide and eventually develop into a complete plant.
In the chapter, F. C. Steward demonstrated regeneration of a complete carrot plant from cultured cells.
Important processes:
- Dedifferentiation: specialised cells regain the ability to divide.
- Cells form an unspecialised mass.
- Redifferentiation: cells become specialised again to form roots, shoots and eventually a complete plant.
Exam keyword: Totipotency = ability of a cell to regenerate an entire plant under suitable conditions.
16. Crown Gall Disease
- Crown gall is a plant disease causing tumour-like swellings.
- It results from rapid, uncontrolled cell division.
- It is caused by the bacterium Agrobacterium tumefaciens.
- Scientists studied its ability to transfer genetic material into plant cells.
- This knowledge became useful in plant tissue culture and genetic engineering.
17. Most Important One-Line Facts
- Tissue: Group of cells working together for a specific function.
- Apical meristem: Increases plant length.
- Lateral meristem: Increases plant girth.
- Intercalary meristem: Helps regeneration after cutting in certain plants.
- Differentiation: Development of specialised structure and function in cells.
- Epidermis: Protective outer covering of plants.
- Parenchyma: Mainly storage; may also photosynthesise.
- Collenchyma: Flexible support.
- Sclerenchyma: Hard and strong support.
- Xylem: Water and mineral transport.
- Phloem: Food transport.
- Epithelial tissue: Covering and lining tissue.
- Connective tissue: Connects and supports body parts.
- Tendon: Muscle to bone.
- Ligament: Bone to bone.
- Skeletal muscle: Voluntary movement.
- Smooth muscle: Involuntary movement in internal organs.
- Cardiac muscle: Rhythmic movement of the heart.
- Neuron: Functional cell of nervous tissue.
- Ball-and-socket: Multidirectional movement.
- Hinge: Mainly one-directional movement.
- Pivot: Rotational movement.
- Fixed joint: No movement.
- Totipotency: Ability of certain plant cells to regenerate a whole plant.
18. High-Priority Exam Questions
Short-answer questions
- Define tissue.
- Why are plant and animal tissues different?
- Name the three types of meristematic tissue.
- Differentiate between xylem and phloem.
- What are the functions of stomata?
- Differentiate between parenchyma, collenchyma and sclerenchyma.
- What are the functions of epithelial tissue?
- Differentiate between tendon and ligament.
- Compare skeletal, smooth and cardiac muscles.
- What are the functions of a neuron?
- What is a joint?
- Name four types of joints with examples.
- Define totipotency and differentiation.
Very likely comparison questions
Xylem vs Phloem
- Xylem → water/minerals
- Phloem → food
Tendon vs Ligament
- Tendon → muscle to bone
- Ligament → bone to bone
Collenchyma vs Sclerenchyma
- Collenchyma → flexible support, living cells
- Sclerenchyma → rigid support, mostly dead cells
Voluntary vs Involuntary movement
- Voluntary → conscious control
- Involuntary → automatic control
Skeletal vs Smooth vs Cardiac muscle
- Skeletal → voluntary, striated
- Smooth → involuntary, non-striated
- Cardiac → involuntary, branched, faintly striated
Last-Minute Revision Map
PLANT TISSUES
Meristematic
→ Apical → length
→ Lateral → girth
→ Intercalary → regeneration
Permanent
→ Simple → Parenchyma / Collenchyma / Sclerenchyma
→ Complex → Xylem / Phloem
ANIMAL TISSUES
Epithelial → covering/lining
Connective → joining/support
Muscular → movement
Nervous → control/communication
MOVEMENT
Muscle → Tendon → Bone → Joint movement
JOINTS
Ball-and-socket → many directions
Hinge → bending/straightening
Pivot → rotation
Fixed → no movement
🌱 What are Tissues?
A tissue is a group of similar cells working together to perform a specific function.
👉 In multicellular organisms, cells don’t work alone — they organize into tissues for efficiency.
🔬 Why are Tissues Important?
- Improve efficiency of work
- Enable division of labour
- Help in forming organs and organ systems
- Allow organisms to perform complex functions
🌿 Plant Tissues
Plant tissues are mainly divided into two types:
1. Meristematic Tissue (Growing Tissue)
These tissues contain actively dividing cells.
🔹 Types:
- Apical Meristem → Found at tips (root & shoot), helps in length growth
- Intercalary Meristem → Found at nodes, helps in regrowth
- Lateral Meristem → Helps in increase in thickness
🔹 Features:
- Cells divide continuously
- Small, dense cytoplasm
- No vacuole or very small
2. Permanent Tissue
Cells that have lost the ability to divide and perform specific functions.
🔹 Types:
(A) Simple Permanent Tissue
Made of one type of cells
- Parenchyma
- Living cells
- Store food, help in photosynthesis
- Collenchyma
- Provide flexibility
- Found in stems and leaves
- Sclerenchyma
- Dead cells
- Provide strength (e.g., coconut husk)
(B) Complex Permanent Tissue
Made of different types of cells
- Xylem
- Transports water and minerals
- Mostly dead cells
- Phloem
- Transports food
- Living cells
🧍 Animal Tissues
Animal tissues are more specialized and are of four main types:
1. Epithelial Tissue (Covering Tissue)
- Covers body surfaces and organs
- Protects, absorbs, and secretes
Types:
- Squamous (thin)
- Cuboidal (cube-shaped)
- Columnar (tall cells)
- Ciliated (movement with cilia)
2. Connective Tissue
- Connects and supports body parts
Examples:
- Blood → transports substances
- Bone → provides structure
- Cartilage → flexible support
- Areolar tissue → fills spaces
3. Muscular Tissue
- Responsible for movement
Types:
- Skeletal muscle → voluntary
- Smooth muscle → involuntary
- Cardiac muscle → heart muscle
4. Nervous Tissue
- Controls and coordinates body functions
- Made of neurons
👉 Carries messages through electrical signals
⚖️ Plant vs Animal Tissues (Quick Difference)
| Feature | Plant Tissue | Animal Tissue |
|---|---|---|
| Growth | Continuous | Limited |
| Support | Mostly dead cells | Mostly living cells |
| Movement | Absent | Present |
| Complexity | Simpler | More complex |