📝 Chapter Notes & Revision

Tissues

🏫 MP BoardClass 9Science

📐 Formula & Cheat Sheet (English)

Quick Revision Notes: Class 9 Science

Chapter: Tissues (ऊतक)

1. Introduction to Tissues

  • Tissue (ऊतक): A group of cells that are similar in structure and/or work together to achieve a particular function.
  • Histology (हिस्टोलॉजी): The study of tissues.
  • Why tissues? Multiorgan organisms have division of labor. Plant and animal tissues differ because plants are stationary (need structural strength/dead cells), while animals are mobile (need more energy/living cells).

2. Plant Tissues (पादप ऊतक)

Plant tissues are broadly divided into two main types based on their dividing capacity:

                  Plant Tissues
                        |
        +---------------+---------------+
        |                               |
Meristematic Tissues            Permanent Tissues
(Dividing Tissues)            (Non-dividing Tissues)
        |                               |
        +-- Apical                      +-- Simple (Parenchyma, Collenchyma, Sclerenchyma)
        +-- Intercalary                 +-- Complex (Xylem, Phloem)
        +-- Lateral

A. Meristematic Tissues (विभज्योतक ऊतक)

  • Cells are actively dividing and responsible for growth.
  • Features: Dense cytoplasm, thin cellulose walls, prominent nuclei, and lack vacuoles.
  • Types:
    1. Apical Meristem: Present at the growing tips of roots and stems. Increases height.
    2. Intercalary Meristem: Located at the base of leaves or internodes (on twigs). Increases length of internodes.
    3. Lateral Meristem (Cambium): Found beneath the bark. Increases girth (thickness) of the stem/root.

B. Permanent Tissues (स्थाई ऊतक)

  • Cells have lost the ability to divide and have taken up a permanent shape, size, and function (Differentiation).
  • Types:
I. Simple Permanent Tissues (सरल स्थाई ऊतक) - Made of only one type of cells:
  1. Parenchyma (पैरेन्काइما):
    • Most common, unspecialized cells with thin walls.
    • Stores food and water.
    • Chlorenchyma: Parenchyma containing chlorophyll; performs photosynthesis.
    • Aerenchyma: Parenchyma with large air cavities found in aquatic plants for buoyancy.
  2. Collenchyma (कॉलेन्काइमा):
    • Living cells with unevenly thickened corners (due to pectin).
    • Provides mechanical support and flexibility (bending of tendrils/stems without breaking).
  3. Sclerenchyma (स्क्लेरेन्काइमा):
    • Dead cells with thick walls containing lignin.
    • Cells are long and narrow. Makes plant hard and stiff (e.g., husk of coconut).
II. Complex Permanent Tissues (जटिल स्थाई ऊतक) - Made of more than one type of cells working together:
  1. Xylem (जाइलम) - Water-conducting tissue:
    • Transports water and minerals upwards from roots to leaves.
    • Components: Tracheids, Vessels (main water-conducting), Xylem parenchyma, and Xylem fibers.
    • Note: Except xylem parenchyma, all other xylem elements are dead.
  2. Phloem (फ्लोएम) - Food-conducting tissue:
    • Transports food from leaves to other parts of the plant.
    • Components: Sieve tubes, Companion cells, Phloem parenchyma, and Phloem fibers.
    • Note: Except phloem fibers (which are dead), all other phloem elements are living.

3. Animal Tissues (जंतु ऊतक)

Animal tissues are grouped into four basic types based on their functions:

A. Epithelial Tissue (उपःकलीय ऊतक)

  • The covering or protective tissue in the animal body.
  • Acts as a barrier to keep different body systems separate.
  • Types:
    • Squamous Epithelium: Extremely thin and flat; forms delicate lining (e.g., mouth lining, blood vessels, lung alveoli).
    • Cuboidal Epithelium: Cube-like cells; forms lining of kidney tubules and salivary glands (provides mechanical support).
    • Columnar Epithelium: Pillar-like, tall cells; found where absorption and secretion occur (e.g., inner lining of intestine). Has microvilli sometimes.
    • Ciliated Epithelium: Columnar or cuboidal cells with hair-like projections called cilia (e.g., in respiratory tract to push mucus forward).
    • Glandular Epithelium: Specialized epithelial cells folded inward to form glands that secrete substances.

B. Connective Tissue (संयोजी ऊतक)

  • Cells are loosely spaced and embedded in an intercellular matrix.
  • Types:
    1. Blood: Fluid connective tissue. Matrix is plasma, containing RBCs, WBCs, and platelets. Transports gases, digested food, hormones, and waste.
    2. Bone: Strong and non-flexible tissue. Matrix is rich in calcium and phosphorus compounds. Provides skeletal support.
    3. Ligaments: Connects bone to bone. Very elastic and has considerable strength.
    4. Tendons: Connects bone to skeletal muscle. Tough and non-elastic.
    5. Cartilage: Solid matrix containing proteins and sugars. Smoothens bone surfaces at joints (found in nose, ear, trachea, larynx).
    6. Areolar Tissue: Found between skin and muscles, around blood vessels and nerves. Fills space inside organs and helps repair tissues.
    7. Adipose Tissue: Fat-storing tissue found below skin and between internal organs. Acts as an insulator.

C. Muscular Tissue (पेशीय ऊतक)

  • Made of muscle fibers; responsible for movement in the body. Contains contractile proteins (actin and myosin).
  • Types:
    1. Striated Muscles (Skeletal / Voluntary):
      • Striped (light and dark bands), voluntary (under our control).
      • Attached to bones (e.g., biceps of arms). Long, cylindrical, unbranched, multinucleated.
    2. Smooth Muscles (Unstriated / Involuntary):
      • No stripes, involuntary (not under our control).
      • Found in walls of blood vessels, stomach, intestine, ureters. Spindle-shaped, uninucleated.
    3. Cardiac Muscles (Heart Muscles):
      • Involuntary, striated, and branched.
      • Show rhythmic contraction and relaxation throughout life without getting fatigued. Uninucleated cells joined by intercalated discs.

D. Nervous Tissue (तंत्रिका ऊतक)

  • Found in the brain, spinal cord, and nerves.
  • Composed of nerve cells or Neurons (तंत्रिका कोशिका).
  • Structure of a Neuron:
    • Cyton (Cell body): Contains nucleus and cytoplasm.
    • Dendrites: Short, branched hair-like projections that receive signals.
    • Axon: A long, single tail-like fiber that transmits impulses away from the cell body.
    • Synapse: The functional junction between two neurons.
  • Function: Responds to stimuli and transmits messages rapidly across the body.

Key Terminology Quick Check

  • Lignin (लिग्निन): A chemical substance acting as cement in plant cell walls (found in Sclerenchyma).
  • Stomata (रंध्र): Tiny pores in epidermis of leaves for gaseous exchange and transpiration, guarded by guard cells.
  • Matrix (मैट्रिक्स / आधात्री): The non-living intercellular ground substance in connective tissues.
  • Voluntary vs. Involuntary: Voluntary muscles are controlled consciously; involuntary muscles work automatically.