1.1 The Cell – A Unit of Life

The Cell Theory

  • Formulated by: Schleiden, Schwann, and Virchow.
  • Key Principles:
    1. All living organisms are composed of one or more cells.
    2. The cell is the basic unit of structure and function in organisms.
    3. Cells arise from pre-existing cells ("Omnis cellula e cellula").
  • Modern Additions: Cells contain hereditary information (DNA), similar chemical composition, energy flow within cells.

Protoplasm and Cytoplasm

  • Protoplasm: The entire living content within the cell membrane (cytoplasm + nucleoplasm).
  • Cytoplasm: Part of protoplasm outside the nucleus, within the cell membrane.
    • Composed of cytosol (fluid portion) and cell organelles.
    • Site of many cellular activities and metabolic pathways.

Prokaryotic vs. Eukaryotic Cells

Feature Prokaryotic Cell Eukaryotic Cell
Nucleus Absent (nucleoid region) Present (true nucleus)
Membrane-bound Organelles Absent Present
Cell Wall Usually present (peptidoglycan) Present in plants/fungi, absent in animals
Ribosomes 70S type 80S type
Size Typically small (0.1-5.0 µm) Typically larger (10-100 µm)

Plant vs. Animal Cells

Feature Plant Cell Animal Cell
Cell Wall Present (cellulose) Absent
Plastids Present (chloroplasts, chromoplasts, leucoplasts) Absent
Vacuoles Large, central vacuole Small, temporary vacuoles
Centrosome Absent (in higher plants) Present

Cell Organelles: The City Within a Cell

  • Cell Wall: (Plants, Fungi) Rigid outer layer, structural support.
  • Cell Membrane: Selectively permeable barrier.
  • Nucleus: Control center, contains DNA.
    • Nucleolus: Site of ribosome synthesis.
  • Mitochondria: "Powerhouses," site of ATP production.
  • Endoplasmic Reticulum (ER): Network of membranes.
    • Rough ER: With ribosomes, protein synthesis.
    • Smooth ER: Lipid synthesis, detoxification.

Cell Organelles: The City Within a Cell (Continued)

  • Ribosomes: Sites of protein synthesis.
  • Golgi Bodies: Modifies, sorts, packages proteins/lipids.
  • Plastids: (Plants) Chloroplasts (photosynthesis), Chromoplasts (pigments), Leucoplasts (storage).
  • Lysosomes: (Mainly animal cells) Digestive enzymes, waste breakdown.
  • Centrosome: (Animal cells) Organizes microtubules for cell division.
  • Vacuole: Storage, turgor pressure (large in plants).