- A cell is the fundamental, structural and functional unit of all living organisms.
- Robert Hooke: Discovered cell.
- Anton Von Leeuwenhoek: First observed and described a live cell.
- The invention of the compound & electron microscopes revealed all the structural details of the cell.
- Matthias Schleiden (1838) observed that all plants are composed of different kinds of cells.
- Theodore Schwann (1839) found that cells have a thin outer layer (plasma membrane). He also found that plant cells have cell wall. He proposed a hypothesis that animals and plants are composed of cells and products of cells.
- Schleiden & Schwann formulated the cell theory.
- Rudolf Virchow (1855) first explained that cells divide and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the cell theory.
- Cell theory states that:
(i) All living organisms are composed of cells and products of cells.
(ii) All cells arise from pre-existing cells.
- All cells contain
o Cytoplasm: A semi-fluid matrix where cellular activities and chemical reactions occur. This keeps the cell in ‘living state’.
o Ribosomes: Non-membrane bound organelles seen in cytoplasm, chloroplasts, mitochondria & on rough ER.
- Cells differ in size, shape and activities.
o Smallest cells: Mycoplasmas (0.3 µm in length).
o Largest isolated single cell: Egg of ostrich.
o Longest cells: E.g. Nerve cell.
o Size of bacteria: 3 to 5 µm (Typical: 1 to 2 µm).
o Human RBCs are about 7.0 µm in diameter.
- Based on the functions, shape of cells may be disc-like, polygonal, columnar, cuboid, thread like, or irregular.
- Cells are 2 types: Prokaryotic cells & Eukaryotic cells.