Lecture Notes on Tissues

Introduction to Cells and Tissues

• Cells are the structural and functional unit of life.
• A single cell performs all basic functions of life (movement, intake of food, respiration, excretion).
• Unicellular organisms: Single cells perform all functions.
• Multicellular organisms: Cells are specialized for efficient functioning.
  • Example:
    • Nerve cells: Carry messages from the brain.
    • Muscle cells: Contract and relax for movement.
    • Blood: Transports oxygen, food, hormones, waste.
    • Plants: Xylem and phloem conduct food and water.

Division of Labor in Multicellular Organisms

• Division of Labor: Specific functions carried out by groups of cells (tissues).
• Definition of Tissue: A group of similar cells working together for a specific function.
  • Example: Nerve tissue.

Objectives of the Lesson

At the end of the lesson, you will be able to:

• Define tissue.
• Identify types of tissues.
• Understand the difference between plant and animal tissues.
• Understand plant tissues and their types.
• Learn about meristematic and permanent tissues.

Differences Between Plant and Animal Tissues

• Plants: Autotrophic, fixed in place, primarily composed of tissues that provide strength and mechanical support (some are dead).
• Animals: Heterotrophic, require more energy, mostly living tissues.
• Growth Patterns:
  • Plants: Growth is limited to specific regions (meristematic).
  • Animals: Uniform growth.
  • Structural organization is more specified in animals.

Types of Plant Tissues

• Two Types Based on Dividing Capacity:
  1. Meristematic Tissues:
     • Continuously divide, found in growth regions.
     • Contribute to length and girth of plants.
  2. Permanent Tissues:
     • Derived from meristematic tissues, lost ability to divide.

Activity on Meristematic Tissues

• Demonstration: Place onion bulbs in water to observe root growth difference.
• Conclusion: Meristematic tissues are found in specific regions, responsible for growth.

Characters of Meristematic Tissues

• Active, thin-walled, living cells.
• Cell wall made of cellulose.
• Shapes: Oval, rounded, polygonal.
• Dense cytoplasm, prominent nuclei.
• Continuous division aids growth.

Types of Meristematic Tissues

• Apical Meristem: Found at growing tips of stems and roots.
• Lateral Meristem: Found on the lateral sides of roots and stems.
• Intercalary Meristem: Located at the base of internodes.

Functions of Meristematic Tissues

• Formation of new cells.
• Apical Meristem: Increases height (primary growth).
• Lateral Meristem: Increases diameter (secondary growth).
• Intercalary Meristem: Lengthens organ.

Permanent Tissues

• Formed when meristematic tissues lose division ability (differentiation).

Characters of Permanent Tissues

• Can be living or dead, thin or thick-walled, mature.
• Shapes: Oval, polygonal, elongated, fiber-like.
• Intercellular spaces present; cytoplasm may be vacuolated.

Activity on Permanent Tissues

• Demonstration: Cut a plant stem, stain, and observe under a microscope to see various cell types.

Types of Permanent Tissues

• Two Types:
  1. Simple Permanent Tissues: Composed of similar cells.
     • Types: Parenchyma, Collenchyma, Sclerenchyma.
  2. Complex Permanent Tissues: Composed of multiple cell types.
     • Types: Xylem, Phloem.

Simple Permanent Tissues

• Parenchyma:
  • Thin primary walls, retains protoplasm.
• Collenchyma:
  • Thick primary walls, retains protoplasm, provides support.
• Sclerenchyma:
  • Lignified secondary walls, dead at maturity, provides rigidity.

Activity on Leaf Cells

• Demonstration: Stretch and break a leaf to observe different layers of cells and the epidermis.
• Structure of Epidermis: Protects plant parts, thicker outer walls, contains stomata (gas exchange).

Functions of Simple Permanent Tissues

• Parenchyma: Packaging, storage, gas exchange.
• Collenchyma: Mechanical support.
• Sclerenchyma: Strength and rigidity.

Complex Permanent Tissues

• Composed of more than one type of cell for a shared function.
• Types:
  • Xylem: Transports water and minerals.
  • Phloem: Transports food materials.

Summary of Key Points

• Tissue Definition: Group of cells similar in structure and function.
• Plant Tissues: Two types - Meristematic and Permanent.
• Meristematic Tissue: Dividing tissue in growth regions.
• Permanent Tissues: Derived from meristematic tissues; classified as simple (parenchyma, collenchyma, sclerenchyma) and complex (xylem, phloem).