CBSE Class 9 Science Notes: Tissues

Concept of Tissues, Organs, and Organ Systems

Let’s dive into the fascinating world of tissues, organs, and organ systems! Understanding these concepts is fundamental to grasping how living organisms are structured and function.

Definitions

• Tissue: A group of similar cells performing a specific function. Think of it as a team of specialized workers.
• Organ: A structure composed of different tissues working together to perform a specific function. Consider it a department within a larger organization.
• Organ System: A group of organs that cooperate to perform a major biological function. This is the entire company, with all the departments working in concert.

Core Principle

The hierarchical organization: Cells -> Tissues -> Organs -> Organ Systems allows for complex functions by dividing labor and increasing efficiency. This organizational structure is a key feature of multicellular organisms.

Animal Tissues

Animal tissues are specialized to perform various functions. We’ll explore the four major types.

Epithelial Tissue

Epithelial tissues cover the body surface, line body cavities, and form glands.

• Functions: Protection, secretion, absorption, excretion, and sensation.
• Types:
  • Squamous (flat cells): Found in the lining of blood vessels and air sacs of lungs.
  • Cuboidal (cube-shaped cells): Found in kidney tubules and glands.
  • Columnar (column-shaped cells): Found in the lining of the stomach and intestines.

Connective Tissue

Connective tissues support and connect different tissues and organs.

• Functions: Binding, support, protection, and transport.
• Types:
  • Blood: Transports substances.
  • Bone: Provides support.
  • Cartilage: Provides flexibility.
  • Loose connective tissue (e.g., areolar tissue): Provides support and flexibility.
  • Dense connective tissue (e.g., tendons and ligaments): Connects muscles to bones and bones to bones.

Muscular Tissue

Muscular tissues enable movement.

• Functions: Contraction and relaxation, enabling movement.
• Types:
  • Skeletal muscle (voluntary): Attached to bones, responsible for body movements.
  • Smooth muscle (involuntary): Found in the walls of internal organs (e.g., stomach, intestines).
  • Cardiac muscle (involuntary): Found in the heart.

Nervous Tissue

Nervous tissue is responsible for communication and control.

• Functions: Conducting nerve impulses, receiving and transmitting information.
• Types:
  • Neurons (nerve cells): Transmit electrical signals.
  • Glial cells (supporting cells): Support and protect neurons.

Plant Tissues

Plant tissues are crucial for the structure and function of plants.

Meristematic Tissue

Meristematic tissues are responsible for plant growth.

• Characteristics: Cells are actively dividing.
• Types:
  • Apical meristem: Found at the tips of roots and shoots, responsible for increasing the length of the plant.
  • Lateral meristem: Found along the sides of the stem and root, responsible for increasing the girth (width) of the plant.

Permanent Tissue

Permanent tissues perform specific functions and are derived from meristematic tissue. They no longer divide.

• Types:
  • Simple permanent tissue: Composed of one type of cell. Includes:
    • Parenchyma (storage and photosynthesis).
    • Collenchyma (provides flexibility).
    • Sclerenchyma (provides rigidity).
  • Complex permanent tissue: Composed of more than one type of cell. Includes:
    • Xylem (transports water and minerals).
    • Phloem (transports food).