Class 9th || Science || Notes || Chapter 6: Tissue

 Introduction to Tissues

• Tissues: A group of cells that have a similar structure and function.
• Cells in multicellular organisms are specialized to perform specific functions, making tissues necessary for efficient biological processes.

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Plant Tissues

1. Meristematic Tissue

• Meristematic tissues are composed of cells that continuously divide, aiding in plant growth.
• These tissues are located in specific regions of the plant, such as the tips of roots and shoots.

Types of Meristematic Tissue

• Apical Meristem: Found at the growing tips of stems and roots, responsible for the increase in length.
• Lateral Meristem: Found in the girth of the plant, responsible for the increase in thickness.
• Intercalary Meristem: Located at the base of leaves or internodes, responsible for the regrowth of leaves and branches.

Characteristics of Meristematic Cells:

• Small, cube-shaped cells
• Thin primary cell walls
• Large nucleus, no vacuole
• Densely packed

2. Permanent Tissue

• After a period of division, meristematic cells differentiate into permanent tissues, which no longer divide but perform specific functions.

Types of Permanent Tissues:

1. Simple Permanent Tissue: Made of similar types of cells.

   • Parenchyma: Loosely packed cells with large intercellular spaces; involved in photosynthesis, storage, and gas exchange.
     • Chlorenchyma: Contains chloroplasts and performs photosynthesis.
     • Aerenchyma: Air-filled spaces to help aquatic plants float.
   • Collenchyma: Provides mechanical support to the plant; cells have unevenly thickened walls.
   • Sclerenchyma: Thick-walled cells that provide strength and rigidity to the plant. These are dead at maturity.
     • Fibres: Elongated cells, providing strength.
     • Sclereids: Short, irregularly shaped cells providing hardness.

2. Complex Permanent Tissue: Made up of more than one type of cell, working together to perform a function.

   • Xylem: Conducts water and minerals from roots to other parts of the plant.
     • Components: Tracheids, Vessels, Xylem Parenchyma, Xylem Fibres
   • Phloem: Transports nutrients (mainly sugars) from leaves to other parts.
     • Components: Sieve Tubes, Companion Cells, Phloem Parenchyma, Phloem Fibres

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Animal Tissues

1. Epithelial Tissue

• Epithelial tissue covers body surfaces, lines organs and cavities, and forms glands. It provides protection, absorption, secretion, and sensation.

Types of Epithelial Tissue:

• Simple Squamous Epithelium: Thin and flat cells, allowing for the exchange of materials (e.g., in lungs).
• Stratified Squamous Epithelium: Layers of cells, providing protection (e.g., skin).
• Cuboidal Epithelium: Cube-shaped cells, involved in absorption and secretion (e.g., in kidneys).
• Columnar Epithelium: Tall cells, involved in secretion and absorption (e.g., in intestines).
• Ciliated Epithelium: Columnar or cuboidal cells with cilia that move materials (e.g., in respiratory tract).

2. Connective Tissue

• Connective tissue supports, connects, and binds various structures of the body.

Types of Connective Tissue:

• Areolar Tissue: Loose connective tissue that fills spaces between organs and supports internal organs.
• Adipose Tissue: Stores fat and provides insulation.
• Bone: Hard and rigid, supporting body structure.
• Cartilage: Smooth tissue at joints, providing flexibility and smooth movement.
• Blood: Fluid connective tissue that transports nutrients, gases, and waste products.
  • Components: Red Blood Cells (RBCs), White Blood Cells (WBCs), Platelets, Plasma

3. Muscular Tissue

• Muscular tissue is responsible for movement and is made up of specialized cells that can contract and relax.

Types of Muscular Tissue:

• Striated Muscle (Skeletal): Voluntary muscles attached to bones for body movement.
• Unstriated Muscle (Smooth): Involuntary muscles found in the walls of internal organs.
• Cardiac Muscle: Specialized muscle found only in the heart, contracting rhythmically to pump blood.

4. Nervous Tissue

• Nervous tissue is responsible for transmitting signals throughout the body.
• Neurons: The basic unit of nervous tissue that transmits impulses.
  • Dendrites: Receive impulses.
  • Axon: Transmits impulses away from the cell body.

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Key Differences Between Plant and Animal Tissues

• Growth: Plant tissues (meristematic) can grow throughout life; animal tissues have limited growth.
• Movement: Animal tissues like muscular and nervous tissues enable movement; plants lack such tissues for movement.
• Types: Plant tissues are more rigid and serve for support and transport, while animal tissues are more diverse for various functions like protection, movement, and communication.

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Summary

• Tissues are groups of cells performing specific functions in plants and animals.
• Plant Tissues: Divided into meristematic and permanent tissues, serving growth and transport.
• Animal Tissues: Include epithelial, connective, muscular, and nervous tissues, each specialized for distinct functions.