Edunes Online Education
BOARD: CBSE and AHSEC (ASSAM)
CLASS: 9 SCIENCE TISSUE
(CBSE Biology – Concept Master Notes)
All living organisms are made up of cells.
A cell is the basic structural and functional unit of life.
This means:
The structure of an organism is built from cells.
All life processes occur within cells.
Examples of life processes:
Nutrition
Respiration
Growth
Excretion
Movement
Reproduction
Definition
Organisms that consist of only one cell are called unicellular organisms.
That single cell performs all life functions.
Example: Amoeba
In Amoeba, one cell performs:
| Life Function | How Amoeba Performs It |
|---|---|
| Movement | By pseudopodia (false feet) |
| Food intake | Engulfs food particles |
| Respiration | Through cell membrane |
| Excretion | Contractile vacuole removes waste |
Thus,
One cell = Whole organism
Examples:
Amoeba
Paramecium
Euglena
Bacteria
Definition
Organisms made up of many cells are called multicellular organisms.
These organisms contain millions or billions of cells.
Examples:
Humans
Animals
Plants
Birds
In multicellular organisms, all cells do not perform the same function.
Instead, cells become specialized.
What is Cell Specialization?
When cells are modified to perform a specific function, it is called cell specialization.
Example in humans:
| Cell Type | Function |
|---|---|
| Muscle cells | Movement by contraction |
| Nerve cells | Carry electrical messages |
| Blood cells | Transport oxygen and nutrients |
Because cells perform only one specific task, they perform it very efficiently.
Definition
When different groups of cells perform different functions, it is called division of labour.
This concept is similar to division of labour in society.
Example:
| System | Function |
|---|---|
| Muscles | Movement |
| Nerves | Communication |
| Blood | Transport |
| Digestive system | Digestion |
Thus,
Different cells + Different functions = Efficient organism
Cells performing the same function are often grouped together.
Definition of Tissue
A tissue is:
A group of cells that are similar in structure and work together to perform a specific function.
Important Features of a Tissue
Cells have similar structure
Cells perform similar functions
Cells are organized together
They increase efficiency of function
| Tissue | Function | Found In |
|---|---|---|
| Blood tissue | Transport of oxygen and nutrients | Animals |
| Muscle tissue | Movement | Animals |
| Phloem tissue | Transport of food | Plants |
| Xylem tissue | Transport of water | Plants |
Thus,
Cells → Tissues → Organs → Organ systems
This is the hierarchical organization of life.
If every cell performed all functions, the body would become inefficient.
Tissues allow:
1. Efficiency
Specialized cells perform tasks better and faster.
2. Division of Labour
Different tissues perform different roles.
3. Coordination
Organ systems work smoothly.
4. Survival of Large Organisms
Large organisms cannot survive with a single cell performing all tasks.
Plants and animals do not have the same types of tissues.
Their tissues are different because their lifestyles are different.
Reason 1: Movement
| Plants | Animals |
|---|---|
| Stationary (fixed in one place) | Move from place to place |
Because plants are stationary:
They need strong supporting tissues
Reason 2: Energy Requirement
| Plants | Animals |
|---|---|
| Produce their own food (photosynthesis) | Search for food |
Animals therefore:
Use more energy
Require active tissues
Reason 3: Type of Cells
| Plants | Animals |
|---|---|
| Many tissues contain dead cells | Most tissues contain living cells |
Dead cells in plants provide:
Strength
Support
Example: Xylem
Plant Growth
Plant growth occurs only in certain specific regions.
These regions contain dividing cells.
Example:
Root tip
Shoot tip
These cells form Meristematic Tissue.
Animal Growth
In animals:
Growth occurs throughout the body.
Cells divide in many parts of the body.
Therefore:
Animals do not have specific growth regions like plants.
Based on ability to divide, plant tissues are classified into:
1. Meristematic Tissue
Actively dividing cells
Responsible for plant growth
2. Permanent Tissue
Cells that have stopped dividing
Perform specific functions
This classification exists only in plants.
Animal bodies are usually more complex than plant bodies.
Reasons:
Animals:
-
Move actively
Search for food
Escape predators
Interact with environment
Therefore animals require:
Highly specialized organs
Complex organ systems
Examples:
Nervous system
Circulatory system
Digestive system
Plants do not require such complex systems.
Remember These Core Ideas
1️⃣ Cells are the basic unit of life
2️⃣ Unicellular organisms perform all functions in one cell
3️⃣ Multicellular organisms have specialized cells
4️⃣ Specialized cells show division of labour
5️⃣ Similar cells form tissues
6️⃣ Plants and animals have different types of tissues
7️⃣ Plant growth occurs in specific regions
8️⃣ Animal growth occurs throughout the body
Cell
The basic structural and functional unit of life.
Tissue
A group of cells with similar structure that work together to perform a particular function.
Division of Labour
Distribution of different functions among different cells or tissues.
Meristematic Tissue
Plant tissue made of actively dividing cells responsible for growth.
Permanent Tissue
Plant tissue formed after cells lose the ability to divide.
Cell \( \Rightarrow \) Tissue \( \Rightarrow \) Organ \( \Rightarrow \) Organ System \( \Rightarrow \) Organism
Example in Humans:
Muscle Cell \( \Rightarrow \) Muscle Tissue \( \Rightarrow \) Heart \( \Rightarrow \) Circulatory System \( \Rightarrow \) Human Body
17. CBSE Exam Questions
Q1. What is a tissue?
Answer:
A tissue is a group of cells that are similar in structure and work together to perform a specific function.
Q2. What is the utility of tissues in multicellular organisms?
Answer:
Tissues are useful because they enable division of labour. Different tissues perform different functions efficiently, allowing complex organisms to survive and function properly.
18. Exam Tip for Students
Whenever the question asks “Why tissues are important?”, remember the 3 keywords:
✔ Division of labour
✔ Specialization
✔ Efficiency
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