Quick Revision Notes: Class 9 Science

Chapter: Tissues (ऊतक)

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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).

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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.

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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.

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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.