Cell: The Unit of Life

🌱 8.1 What is a Cell?

  • All living things (organisms) are made of cells 🧫.
  • Unicellular organisms (like bacteria) have one cell and live independently.
  • Multicellular organisms (like humans) have many cells working together.
  • 💡 Key fact: A cell is the smallest unit that can perform life functions. Anything smaller can’t live alone!
  • History: Anton Von Leeuwenhoek first saw live cells. Robert Brown discovered the nucleus.

📜 8.2 Cell Theory

  • Matthias Schleiden (1838): Studied plants 🌿 and said “All plants are made of cells!”
  • Theodore Schwann (1839): Studied animals 🐇 and found:
    • Cells have a plasma membrane (thin outer layer).
    • Plant cells have a cell wall (unique to plants).
    • Proposed: “Animals and plants are made of cells + cell products!”
  • Rudolf Virchow (1855): Solved the mystery of new cells:
    “All cells come from pre-existing cells!” (Omnis cellula-e cellula) 🔄

⭐ Modern Cell Theory ⭐

  1. All living things are made of cells and cell products.
  2. New cells come from pre-existing cells.

🔬 8.3 Cell Overview

  • Plant cell (e.g., onion):
    • Outer cell wall + inner cell membrane.
  • Animal cell (e.g., human cheek):
    • Only cell membrane as outer layer.
  • Nucleus:
    • Dense, membrane-covered control center 🎯.
    • Holds chromosomes (with DNA).
  • Eukaryotic cells: Have a nucleus (e.g., plants, animals).
  • Prokaryotic cells: No nucleus (e.g., bacteria).
  • Cytoplasm: Jelly-like fluid filling the cell where life activities happen! 🧪

🧩 Organelles

  • Eukaryotic organelles (membrane-bound):
    • Endoplasmic reticulum, Golgi complex, Lysosomes, Mitochondria, Vacuoles.
  • Prokaryotes: Have no membrane-bound organelles.
  • Ribosomes (all cells):
    • Make proteins 🧬.
    • Found in cytoplasm, chloroplasts (plants), mitochondria, and rough ER.
  • Centrosome (animal cells only): Helps in cell division ➗.

Fun fact: Cells vary in size! Smallest = Mycoplasma (0.3 μm), Bacteria = a few μm.

🚀 NEET Must-Know Concepts

  1. Cell theory postulates: All living things made of cells; cells arise from pre-existing cells.
  2. Prokaryotes vs Eukaryotes: Presence/absence of a membrane-bound nucleus.
  3. Ribosomes: Non-membrane organelles making proteins in ALL cells.
  4. Cell organelles: Know membrane-bound ones (mitochondria, ER, etc.) in eukaryotes.
  5. Key contributions: Schleiden (plants), Schwann (animals), Virchow (cell division).