The Fundamental Unit of Life

• Introduction

  • Cell: Structural and functional unit of life
  • Discovery by Robert Hooke (1665) using primitive microscope
  • Leeuwenhoek discovered free-living cells in pond water
  • Cell Theory: Schleiden and Schwann (All plants/animals are composed of cells)
  • Virchow: All cells come from pre-existing cells
  • Unicellular (Amoeba, Paramecium) vs Multicellular (Plants, Animals)

• Plasma Membrane (Cell Membrane)

  • Outer covering of the cell
  • Selectively permeable
  • Made of lipids and proteins
  • Diffusion: Movement of molecules from high to low concentration
  • Osmosis: Diffusion of water across a selectively permeable membrane
    • Hypotonic solution: Cell swells (endosmosis)
    • Isotonic solution: Cell size remains same
    • Hypertonic solution: Cell shrinks (exosmosis)
  • Endocytosis: Engulfing food/materials (e.g., Amoeba)

• Cell Wall

  • Found only in plant cells (outside plasma membrane)
  • Rigid and non-living
  • Made of cellulose
  • Provides structural strength and prevents bursting in hypotonic medium
  • Plasmolysis: Shrinkage of plant cytoplasm away from cell wall

• Nucleus

  • Brain of the cell / Control center
  • Double-layered nuclear membrane with pores
  • Contains chromosomes (DNA and proteins)
  • Genes: Functional units of DNA
  • Plays central role in cellular reproduction

• Cytoplasm

  • Fluid content inside plasma membrane
  • Contains various specialized cell organelles

• Cell Organelles

  • Endoplasmic Reticulum (ER)
    • Network of membrane-bound tubes/sheets
    • Rough ER (RER): Has ribosomes, synthesizes proteins
    • Smooth ER (SER): Lacks ribosomes, synthesizes lipids/fats and detoxifies poisons
  • Golgi Apparatus
    • System of membrane-bound vesicles (cisternae)
    • Function: Storage, modification, and packaging of products
    • Formation of lysosomes
  • Lysosomes
    • Membrane-bound sacs filled with digestive enzymes
    • Waste disposal system ("Suicide bags" of the cell)
  • Mitochondria
    • Powerhouse of the cell
    • Double membrane (inner folded into cristae)
    • Generates energy in the form of ATP (Adenosine Triphosphate)
    • Has its own DNA and ribosomes
  • Plastids
    • Found only in plant cells
    • Chromoplasts: Colored plastids (contain pigments like chlorophyll)
    • Leucoplasts: Colorless plastids (store starch, oils, protein)
    • Chloroplasts: Photosynthesis site (contain chlorophyll)
  • Vacuoles
    • Storage sacs for solid or liquid contents
    • Large and central in plant cells (provides turgidity)
    • Small in animal cells

• Cell Division

  • Mitosis
    • Growth and repair division
    • Produces two identical daughter cells (same chromosome number)
  • Meiosis
    • Reproduction division
    • Produces four daughter cells with half the chromosome number (gametes)