Introduction and Structure of the Cell

Jun 22, 2025

Overview

This lecture covers the entire concept of "Cell - The Unit of Life," including cell structure, types, major scientific discoveries, cell theory, and main organelles.

Definition and Importance of the Cell

  • "Cell is the structural and functional unit of life" - the smallest unit of life.
  • All living organisms are made up of cells or products of cells.
  • There are unicellular and multicellular organisms.

Prokaryotic and Eukaryotic Cells

  • Prokaryotic cells do not have a well-defined nucleus or nuclear membrane.
  • Eukaryotic cells have a well-defined nucleus, double membrane-bound.
  • Prokaryotic: plasmid, nucleoid, cell wall, fimbriae, mesosome, chromatophore, etc.
  • Mycoplasma is the smallest living cell; viruses are not living.

Cell Theory and Scientific Discoveries

  • 1665: Robert Hooke first observed dead cells.
  • 1831: Robert Brown discovered the nucleus.
  • 1838-39: Schleiden (plant) and Schwann (animal) proposed cell theory.
  • 1855: Rudolf Virchow said "Omnis cellula e cellula."
  • Electron microscope revealed structures like ribosomes (1953).

Basic Components of the Cell

  • Cell membrane: lipid bilayer, proteins, carbohydrates, cholesterol present.
  • Cytoplasm: site of all metabolic reactions.
  • Ribosome: protein factory, 70s (prokaryotic), 80s (eukaryotic), not membrane-bound.
  • Nucleus: chromatin, chromosomes, nucleolus (rRNA factory).

Organelles and Their Functions

  • Endoplasmic reticulum (rough/smooth): protein/lipid synthesis.
  • Golgi complex: packaging and transport, glycosylation.
  • Lysosome: digestive enzymes ("suicide bags").
  • Vacuole: storage, tonoplast membrane.
  • Mitochondria: double membrane, ATP production, semi-autonomous.
  • Chloroplast: photosynthesis, grana/stroma, own DNA.
  • Cilia/flagella: for movement, 9+2 microtubule arrangement.

Differences Between Plant and Animal Cells (Four 'C's)

  • Cell wall, central vacuole, chloroplast (only in plants), centriole (only in animals).

Key Terms & Definitions

  • Cell тАФ structural and functional unit of life.
  • Prokaryotic cell тАФ cell without a well-defined nucleus.
  • Eukaryotic cell тАФ cell with a well-defined nucleus.
  • Ribosome тАФ site of protein synthesis.
  • Endoplasmic reticulum тАФ protein/lipid synthesis.
  • Golgi complex тАФ packaging and transport.
  • Lysosome тАФ digestive organelle.
  • Mitochondria тАФ organelle for energy (ATP) production.
  • Chloroplast тАФ site of photosynthesis in plants.
  • Cytoplasm тАФ fluid part of the cell where most activities occur.

Action Items / Next Steps

  • Print your notes and revise them repeatedly.
  • Next chapter: "Cell Cycle and Cell Division" to be read.
  • Solve past 5 years' PYQs.
  • Read Botany Made Easy (Med-Easy) and NCERT together.

Full transcript