8. CELL: THE UNIT OF LIFE
- 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.
CELL THEORY
- 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.
AN OVERVIEW OF CELL
- 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.
- Topic 1: Cell Theory, Overview of cells
- Topic 2: Prokaryotic cell
- Topic 3: Eukaryotic cell - 1
- Topic 4: Eukaryotic cell - 2
