Tissues Class 9 Science Notes Chapter 6

Tissue Short Notes | Class 9

What is a Tissue?

A tissue is a group of cells that collectively perform a particular function. In multicellular organisms, tissues constitute the building blocks of organs, and they specialize in performing different functions such as support, transport, or secretion.

Types of Tissues

Tissues are broadly classified into two categories based on the organism:

  1. Plant Tissues
  2. Animal Tissues

1. Plant Tissues

Plant tissues are classified into two categories:

  1. Meristematic Tissue (Growth tissue)
  2. Permanent Tissue (Tissue that has ceased to divide)

Meristematic Tissue

  • Location: Present in areas of plant growth such as the tips of shoots and roots.
  • Function: Involved in plant growth.
  • Types:

  1. Apical Meristem: Present at the tip of roots and shoots, involved in primary growth.
  2. Lateral Meristem: Present in the sides of stems and roots, involved in secondary growth.
  3. Intercalary Meristem: Present at the base of leaves or internodes, involved in the growth of leaves and internodes.

Permanent Tissue

Developed from meristematic tissues, these cells lose the power of division and become specialized to perform specific functions.

  • Types:

1. Simple Permanent Tissue: Composed of similar types of cells.
  • Parenchyma: Allows storage, photosynthesis (if chloroplasts are present), and floating (if air spaces are present). Present in soft parts of plants.
  • Collenchyma: Provides mechanical support and elasticity, present in leaf stalks and beneath the epidermis.
  • Sclerenchyma: Provides strength, composed of dead cells with thick walls, present in seeds, nuts, and fibers.
2. Complex Permanent Tissue: Composed of different types of cells.

  • Xylem: Carrying water and minerals from roots to other parts of the plant. Constituents: tracheids, vessels, xylem fibers, and xylem parenchyma.
  • Phloem: Carrying food from leaves to other parts. Constituents: sieve tubes, companion cells, phloem fibers, and phloem parenchyma.

2. Animal Tissues

Animal tissues are divided into four broad categories:

  1. Epithelial Tissue
  2. Connective Tissue
  3. Muscular Tissue
  4. Nervous Tissue

1. Epithelial Tissue:

<<Function: Forms the covering or lining of body structures (e.g., skin, inner lining of the mouth).

Types:

  • Squamous Epithelium: Thin and flat, lines blood vessels and alveoli.
  • Cuboidal Epithelium: Cube-shaped, present in glands and kidney tubules.
  • Columnar Epithelium: Tall and pillar-like, present in the intestine.
  • Ciliated Epithelium: Has cilia, present in respiratory tract.
  • Glandular Epithelium: Specialized for secretion, present in glands.

2. Connective Tissue:

<<Function: Binds and supports other tissues and organs.

Types:

  • Blood: Carries nutrients, oxygen, and waste.
  • Bone: Gives structure and support.
  • Cartilage: Gives flexibility, present in nose, ears, and joints.
  • Tendons: Connects muscle to bones.
  • Ligaments: Connects bones to bones.
  • Adipose Tissue: Stores fat, insulates body.

3. Muscular Tissue:

Function: Assists in movement by contracting and relaxing.

Types:

  • Striated Muscle: Also known as skeletal muscle, voluntary in nature, attached to bones.
  • Smooth Muscle: Involuntary, present in walls of internal organs (e.g., stomach, intestine).
  • Cardiac Muscle: Involuntary, present only in the heart, pumps blood.

4. Nervous Tissue:

Function: Receives stimuli and transmits impulses. Neurons, the cells of nervous tissue, are the ones that carry signals throughout the body.

Key Points to Remember:

Tissues are groups of similar cells with specialized functions.

Plant tissues consist of meristematic (growth) and permanent tissues (support and transport).

Animal tissues are classified as epithelial (covering), connective (binding), muscular (movement), and nervous (communication).