CELL DIVISION AND TISSUE

CELL DIVISION
• Cell division is the process by which a parent cell divides into two or more daughter cells.
• It is essential for growth, repair, reproduction and continuity of life.
• The process of cell division was first observed by Walther Flemming in the early 1880s.

Types of Cell Division
• Amitosis
• Mitosis
• Meiosis

Amitosis (Binary Fission)
• It is the simplest form of cell division.
• The parent cell directly divides into two daughter cells without distinct stages.
• No spindle formation or chromosome organization is observed.
• Commonly seen in primitive and less developed organisms.
• Example:
  – Bacteria
• Also known as binary fission.

Mitosis
• Occurs in somatic (body) cells.
• Responsible for growth, tissue repair and regeneration.
• Produces two genetically identical daughter cells.
• Maintains the chromosome number of the parent cell.
• Important for:
  – Growth of multicellular organisms
  – Healing of wounds
  – Replacement of dead or worn-out cells

Meiosis
• Occurs in reproductive cells (germ cells).
• Produces four genetically different daughter cells.
• Chromosome number is reduced to half.
• Essential for sexual reproduction.
• Maintains genetic variation in populations.

TISSUE
• A tissue is a group of cells that are similar in structure and function and work together to perform a specific function.

Classification of Tissues
• Plant Tissues
• Animal Tissues

PLANT TISSUE

Types of Plant Tissue
• Meristematic Tissue
• Permanent Tissue

Meristematic Tissue
• Consists of actively dividing cells.
• Responsible for growth in plants.
• Cells are:
  – Small
  – Thin-walled
  – Dense cytoplasm
  – Large nucleus

Types of Meristematic Tissue (Based on Location)
• Apical Meristem
  – Present at the tips of roots and shoots
  – Increases length of plant

• Lateral Meristem
  – Present in stems and roots
  – Responsible for increase in girth (thickness)

• Intercalary Meristem
  – Present at the base of leaves or internodes
  – Helps in elongation of plant parts

PERMANENT TISSUE
• Formed after differentiation of meristematic cells.
• Cells lose the ability to divide.

Types of Permanent Tissue
• Simple Permanent Tissue
• Complex Permanent Tissue
• Protective Tissue

Simple Permanent Tissue
• Consists of only one type of cell.

Types:
• Parenchyma
  – Living cells
  – Thin cell walls
  – Storage of food
  – Photosynthesis (in chlorenchyma)

• Collenchyma
  – Living cells
  – Unevenly thickened cell walls
  – Provides flexibility and support

• Sclerenchyma
  – Dead cells
  – Thick lignified walls
  – Provides strength and rigidity

Complex Permanent Tissue
• Made up of more than one type of cell.
• Helps in transportation of substances.

Types:
• Xylem
  – Conducts water and minerals from roots to other parts
  – Components:
    • Vessels
    • Tracheids
    • Xylem fibres
    • Xylem parenchyma

• Phloem
  – Transports food from leaves to other parts
  – Components:
    • Sieve tubes
    • Companion cells
    • Phloem fibres
    • Phloem parenchyma

Protective Tissue
• Protects plants from injury and water loss.

Types:
• Epidermis
  – Outer protective layer
  – Contains stomata
  – Helps in transpiration and gaseous exchange

• Cork
  – Found in mature stems and roots
  – Dead cells
  – Cell walls impregnated with suberin
  – Prevents water loss and infection

ANIMAL TISSUE

Types of Animal Tissue
• Epithelial Tissue
• Connective Tissue
• Muscular Tissue
• Nervous Tissue

Epithelial Tissue
• Forms protective covering of body surfaces.
• Lines internal organs and cavities.
• Cells are tightly packed with little intercellular space.
• Functions:
  – Protection
  – Absorption
  – Secretion

Connective Tissue
• Connects, supports and binds body parts.
• Cells are embedded in an extracellular matrix.

Types:
• Fibrous Connective Tissue
  – Tendons (connect muscles to bones)
  – Ligaments (connect bones to bones)

• Skeletal Connective Tissue
  – Bone
  – Cartilage
  – Provides support and protection

• Fluid Connective Tissue
  – Blood
  – Lymph

Blood
• Fluid matrix called plasma.
• Components:
  – Red Blood Cells (RBCs)
  – White Blood Cells (WBCs)
  – Platelets

Muscular Tissue
• Made up of elongated muscle fibres.
• Responsible for movement of body parts.
• Contains contractile proteins.
• Types:
  – Skeletal muscles
  – Smooth muscles
  – Cardiac muscles

Nervous Tissue
• Found in brain, spinal cord and nerves.
• Made up of neurons (nerve cells).
• Highly sensitive and excitable.
• Responsible for transmission of nerve impulses.
• Helps in coordination and control of body activities.

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Subject: Science

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