In multicellular organisms like animals, cells are organized into tissues, tissues form organs, and organs work together as organ systems. This hierarchical organization allows efficient functioning and coordination of various life processes.
This chapter mainly focuses on animal tissues and the structural organization of organisms like cockroach, frog, and earthworm.
Animal Tissues
A tissue is a group of similar cells that perform a specific function.
Animal tissues are classified into four main types:
- Epithelial tissue
- Connective tissue
- Muscular tissue
- Neural tissue
1. Epithelial Tissue
Definition
Epithelial tissue forms the outer covering of the body and lines internal organs and cavities.
Characteristics
- Cells are tightly packed
- Little or no intercellular space
- Rest on a basement membrane
- Avascular (no blood vessels)
Types of Epithelial Tissue
1. Simple Epithelium
It consists of a single layer of cells.
Types:
- Squamous epithelium: Thin and flat cells for diffusion (e.g., alveoli)
- Cuboidal epithelium: Cube-shaped cells for secretion and absorption
- Columnar epithelium: Tall cells for absorption and secretion
- Ciliated epithelium: Helps in movement of substances
2. Compound Epithelium
- Multilayered
- Provides protection
- Example: Skin
2. Connective Tissue
Definition
Connective tissue connects, supports, and binds different parts of the body.
Components
- Cells
- Fibers (collagen, elastic)
- Matrix (ground substance)
Types of Connective Tissue
1. Loose Connective Tissue
- Areolar tissue
- Adipose tissue (fat storage)
2. Dense Connective Tissue
- Tendons (connect muscle to bone)
- Ligaments (connect bone to bone)
3. Specialized Connective Tissue
Blood
- Fluid connective tissue
- Transports gases, nutrients, and wastes
Bone
- Hard and rigid
- Provides support and protection
Cartilage
- Flexible
- Present in joints and nose
3. Muscular Tissue
Definition
Muscular tissue is responsible for movement due to contraction and relaxation.
Types of Muscles
1. Skeletal Muscle
- Voluntary
- Striated
- Attached to bones
2. Smooth Muscle
- Involuntary
- Non-striated
- Found in internal organs
3. Cardiac Muscle
- Involuntary
- Striated
- Found in heart
4. Neural Tissue
Definition
Neural tissue is responsible for transmission of impulses.
Components
- Neurons (nerve cells)
- Neuroglia (supporting cells)
Structure of Neuron
- Cell body
- Dendrites
- Axon
Organ and Organ System
- Organ: Group of tissues performing a specific function
- Organ system: Group of organs working together
Earthworm (Brief Structure)
Key Features
- Body segmented (metamerism)
- Closed circulatory system
- Respiration through skin
- Hermaphrodite
Cockroach (Brief Structure)
Key Features
- Body divided into head, thorax, abdomen
- Open circulatory system
- Tracheal respiration
- Jointed appendages
Frog (Brief Structure)
Key Features
- Amphibian (lives on land and water)
- Moist skin
- Three-chambered heart
- Respiration through lungs and skin
Important Differences
Bone vs Cartilage
| Feature | Bone | Cartilage |
|---|---|---|
| Nature | Hard | Flexible |
| Matrix | Calcified | Non-calcified |
Voluntary vs Involuntary Muscles
| Feature | Voluntary | Involuntary |
|---|---|---|
| Control | Conscious | Automatic |
| Example | Skeletal | Smooth |
Important NEET & CBSE Points
- Epithelial tissue → covering and protection
- Connective tissue → support and transport
- Muscle tissue → movement
- Neural tissue → coordination
- Earthworm → closed circulation
- Cockroach → open circulation
Quick Revision Notes
- Tissue → group of cells
- Epithelium → protection
- Muscle → movement
- Neuron → impulse transmission
- Organ → group of tissues
Frequently Asked Questions (FAQs)
Q1. What are tissues?
Groups of similar cells performing specific functions.
Q2. What is epithelial tissue?
Tissue covering body surfaces.
Q3. What is the function of connective tissue?
Support and binding.
Q4. What is a neuron?
Basic unit of nervous system.
Conclusion
Structural organisation in animals explains how cells, tissues, and organs are arranged to perform complex functions. This chapter is very important for CBSE exams and NEET, especially for conceptual understanding and diagram-based questions.