Understanding Cells: The Building Blocks of Life

🔬 Key Historical Discoveries

  • Schwann (1839) discovered the plasma membrane in animal cells 🐾
  • He identified cell walls as unique to plant cells 🌱
  • Schleiden & Schwann proposed: All living things are made of cells and cell products
  • Rudolf Virchow (1855) added: New cells come from pre-existing cells 🔄 (Omnis cellula-e cellula)

🧪 Modern Cell Theory

  1. All living organisms are made of cells and their products
  2. All cells arise from pre-existing cells

🔍 Basic Cell Structure

Eukaryotic Cells (with nucleus):

  • Have a membrane-bound nucleus containing DNA 🧬
  • Include organelles: Endoplasmic Reticulum, Golgi, Lysosomes, Mitochondria, Vacuoles
  • Examples: Plant cells 🌿 (with cell wall) & animal cells 🐾 (without cell wall)

Prokaryotic Cells (no nucleus):

  • No membrane-bound nucleus
  • Lack membrane-bound organelles
  • Examples: Bacteria, Blue-green algae, Mycoplasma

Both cell types have:

  • Cytoplasm – Semi-fluid matrix where cellular activities occur 🌀
  • Ribosomes – Non-membrane structures that make proteins 💪

🌈 Amazing Cell Diversity

Sizes:

  • Smallest: Mycoplasma (0.3 μm)
  • Bacteria: 3-5 μm
  • Largest single cell: Ostrich egg 🥚
  • Human RBC: 7.0 μm diameter
  • Longest cells: Nerve cells

Shapes: (See Figure 8.1)

  • RBCs: Round & biconcave
  • White blood cells: Amoeboid
  • Nerve cells: Branched & long
  • Epithelial cells: Columnar
  • Mesophyll cells: Round/oval
  • Shape relates to function! 🎯

🦠 Prokaryotic Cells

Features:

  • Smaller than eukaryotic cells
  • Multiply rapidly ⚡
  • Fundamental organization same despite shape variations

Bacterial Shapes:

  • Bacillus: Rod-like 🥖
  • Coccus: Spherical ⚽
  • Vibrio: Comma-shaped ⛵
  • Spirillum: Spiral 🌀

💡 NEET Must-Knows

  1. Cell Theory – 2 principles + Virchow’s contribution
  2. Eukaryotic vs Prokaryotic – Nucleus presence, organelles, examples
  3. Cell Size & Shape – Mycoplasma (smallest), ostrich egg (largest), nerve cells (longest)
  4. Prokaryotic Features – Bacterial shapes, rapid multiplication
  5. Universal Cell Structures – Ribosomes (all cells), cytoplasm (all cells)