1. What is a Tissue?
✅ Key Definition
A tissue is a group of similar cells that work together to perform a specific function.
🌱 Why Do We Need Tissues?
In unicellular organisms like Amoeba, one cell performs all functions.
But in multicellular organisms (like humans and plants):
- Different cells perform different functions.
- This is called division of labour.
- To perform specific functions efficiently, similar cells group together and form tissues.
Example:
- Muscle cells form muscle tissue (for movement).
- Nerve cells form nervous tissue (for control).
📌 Flow of Organisation
Cells → Tissues → Organs → Organ Systems → Organism
🧠 Exam Tip
The definition of tissue is very important for 1 mark.
Always write: “Group of similar cells performing a specific function.”
2. Plant Tissues
Plant tissues are divided into two main types:
- Meristematic Tissue
- Permanent Tissue
2.1 Meristematic Tissue
✅ Definition
Meristematic tissue consists of actively dividing cells that are responsible for plant growth.
🌿 Characteristics
- Cells divide continuously.
- Cells are small in size.
- Thin cell wall.
- Dense cytoplasm.
- Prominent nucleus.
- Vacuoles are absent or very small.
- No intercellular spaces.
📚 Types of Meristematic Tissue
1️⃣ Apical Meristem
- Present at root and shoot tips.
- Helps in increase in length of plant.
2️⃣ Intercalary Meristem
- Present at nodes.
- Helps in growth of internodes.
3️⃣ Lateral Meristem
- Present at sides of stem.
- Helps in increase in girth (thickness).
🖊 Diagram Description
In a stem diagram:
- Label the top tip as Apical meristem
- Label side region as Lateral meristem
- Label node region as Intercalary meristem
🧠 Memory Trick
A–I–L
Apical → Increase in Length
Intercalary → Between nodes
Lateral → Increase in thickness
2.2 Permanent Tissue
✅ Definition
Permanent tissues are formed from meristematic tissues. Their cells lose the power of division and perform specific functions.
Permanent tissues are of three types:
- Simple Permanent Tissue
- Complex Permanent Tissue
- Protective Tissue
2.2.1 Simple Permanent Tissue
Made up of only one type of cells.
🌿 (A) Parenchyma
Definition:
Living tissue with thin cell walls and intercellular spaces.
Functions:
- Storage of food
- Photosynthesis (if chlorophyll present → Chlorenchyma)
- Provides buoyancy in aquatic plants (Aerenchyma)
🌿 (B) Collenchyma
Definition:
Living tissue with unevenly thickened cell corners.
Function:
- Provides flexibility and support.
Example: Leaf stalk.
🌿 (C) Sclerenchyma
Definition:
Dead tissue with thick and lignified cell walls.
Function:
- Provides strength and hardness.
Example: Coconut husk.
📊 Comparison Table
| Feature | Parenchyma | Collenchyma | Sclerenchyma |
|---|---|---|---|
| Nature | Living | Living | Dead |
| Cell wall | Thin | Uneven thick | Very thick |
| Function | Storage | Support | Strength |
🧠 Important Point
Living tissues → Parenchyma & Collenchyma
Dead tissue → Sclerenchyma
2.2.2 Complex Permanent Tissue
Made up of more than one type of cells.
🌿 (A) Xylem
Function:
Transports water and minerals from roots to other parts.
Components:
- Tracheids
- Vessels
- Xylem fibres
- Xylem parenchyma
Most parts are dead.
🌿 (B) Phloem
Function:
Transports food from leaves to other parts.
Components:
- Sieve tubes
- Companion cells
- Phloem fibres
- Phloem parenchyma
Mostly living tissue.
🧠 Exam Tip
Xylem → Water
Phloem → Food
Very commonly asked in 2–3 mark questions.
2.2.3 Protective Tissue
🌿 Epidermis
- Outer covering of plant.
- Protects plant.
- Has stomata for gas exchange.
🌿 Cork
- Formed by lateral meristem.
- Cells are dead.
- Waterproof due to suberin.
3. Animal Tissues
Animal tissues are of four types:
- Epithelial
- Connective
- Muscular
- Nervous
3.1 Epithelial Tissue
Definition:
Tissue that covers body surfaces and lines internal organs.
Types:
Squamous
- Thin and flat.
- Helps in diffusion. Example: Lungs.
Cuboidal
- Cube-shaped.
- Helps in secretion. Example: Kidney tubules.
Columnar
- Long cells.
- Helps in absorption. Example: Intestine.
Ciliated
- Has hair-like structures.
- Moves substances. Example: Respiratory tract.
Glandular
- Secretes substances.
Important Point
Cells are tightly packed with no intercellular space.
3.2 Connective Tissue
Definition:
Tissue that connects, supports and binds different parts of body.
Types:
- Areolar tissue (packing tissue)
- Adipose tissue (fat storage)
- Bone (hard support)
- Cartilage (flexible support)
- Blood (fluid connective tissue)
Blood Components:
- RBC
- WBC
- Platelets
- Plasma
🧠 Important
Blood is connective tissue because it transports materials.
3.3 Muscular Tissue
Types:
Striated Muscle
- Voluntary
- Present in limbs
Smooth Muscle
- Involuntary
- Present in stomach
Cardiac Muscle
- Involuntary
- Present in heart
- Branched fibres
Exam Tip
Striations are present only in striated muscle.
3.4 Nervous Tissue
Definition:
Tissue responsible for control and coordination.
Structure of Neuron:
- Cell body
- Dendrites
- Axon
Function:
Transmits nerve impulses.
Diagram Description
Draw a neuron:
- Central cell body
- Short branches → Dendrites
- Long extension → Axon
🌟 Quick Revision Summary
Plant Tissues
- Meristematic → Growth
- Permanent → Function
Simple → Parenchyma, Collenchyma, Sclerenchyma
Complex → Xylem (water), Phloem (food)
Animal Tissues
- Epithelial → Covering
- Connective → Support
- Muscular → Movement
- Nervous → Control
