Class 9 Science – Chapter 6: Tissues (Detailed Notes)

Class 9 Science – Chapter 6: Tissues (Detailed Notes)

1. What is a Tissue?

• A tissue is a group of similar cells that perform a specific function.
• Organisms are made up of tissues, which form organs, and organs form organ systems.
• Plants and animals have different types of tissues because of their different lifestyles.

2. Plant Tissues

Plant tissues are of two types:

• Meristematic Tissues – Actively dividing cells.
• Permanent Tissues – Cells that have lost their ability to divide.

2.1 Meristematic Tissue

• Cells are small, thin-walled, with large nuclei and no vacuoles.
• Types:
  • Apical Meristem: Present at root and shoot tips; responsible for primary growth.
  • Intercalary Meristem: Present at nodes; helps in growth of internodes (e.g., grasses).
  • Lateral Meristem: Present along sides of stems and roots; helps in secondary growth (e.g., cambium).

2.2 Permanent Tissue

• Formed from meristematic tissue; cells do not divide.
• Types:
  • Simple Permanent Tissue (Made of similar cells)
  • Complex Permanent Tissue (Made of different types of cells)

Simple Permanent Tissues:

(a) Parenchyma

• Living cells with thin walls and large vacuoles.
• Functions: Storage, photosynthesis, and support.
• Chlorenchyma: Parenchyma with chloroplasts (photosynthesis).
• Aerenchyma: Parenchyma with air spaces (buoyancy in aquatic plants).

(b) Collenchyma

• Living, elongated cells with unevenly thickened walls.
• Function: Provides mechanical support and flexibility (e.g., petioles, stems).

(c) Sclerenchyma

• Dead cells with thick lignified walls and no protoplasm.
• Function: Provides hardness and strength (e.g., coconut husk).

Complex Permanent Tissues:

(a) Xylem

• Conducts water and minerals from roots to other parts.
• Components: Tracheids, Vessels, Xylem parenchyma, Xylem fibres.
• Mostly dead tissues, except Xylem parenchyma.

(b) Phloem

• Transports food from leaves to other parts of the plant.
• Components: Sieve tubes, Companion cells, Phloem fibres, Phloem parenchyma.
• Living tissue, except Phloem fibres.

3. Animal Tissues

Types of Animal Tissues:

• Epithelial Tissue
• Connective Tissue
• Muscular Tissue
• Nervous Tissue

3.1 Epithelial Tissue

• Protective tissue forming the outer and inner lining of organs.
• Types:
  • Simple squamous: Flat cells (e.g., walls of blood vessels).
  • Stratified squamous: Multiple layers (e.g., skin).
  • Columnar: Tall, pillar-like cells (e.g., intestine).
  • Ciliated: Columnar cells with cilia (e.g., respiratory tract).
  • Cuboidal: Cube-shaped cells (e.g., kidney tubules).

3.2 Connective Tissue

• Supports and binds other tissues and organs.
• Types:
  • Areolar tissue: Fills spaces between organs.
  • Adipose tissue: Stores fat and provides insulation.
  • Bone: Hard tissue providing structural support.
  • Cartilage: Smooth tissue at joints, flexible.
  • Tendon: Connects muscle to bone.
  • Ligament: Connects bone to bone.
  • Blood: Fluid connective tissue that transports gases, nutrients, etc.

3.3 Muscular Tissue

• Responsible for movement.
• Types:
  • Skeletal muscles: Voluntary, striated, multinucleated.
  • Smooth muscles: Involuntary, non-striated (e.g., stomach, intestines).
  • Cardiac muscles: Involuntary, striated, found only in the heart.

3.4 Nervous Tissue

• Found in brain, spinal cord, and nerves.
• Made up of neurons and supporting cells.
• Function: Transmits messages between different parts of the body.