Cell The Unit of Life - Notes | Class 11 | Part 1: Cell theory, An Overview of Cell
Cell: The Unit of Life - Cell Theory and Overview
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 and 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 a cell wall. He proposed a hypothesis that animals and plants are composed of cells and products of cells.
Schleiden and 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:
All living organisms are composed of cells and products of cells.
All cells arise from pre-existing cells.
An Overview of Cell
All cells contain:
Cytoplasm: A semi-fluid matrix where cellular activities and chemical reactions occur. This keeps the cell in a ‘living state’.
Ribosomes: Non-membrane bound organelles seen in cytoplasm, chloroplasts, mitochondria, and on rough ER.
Cells differ in size, shape, and activities.
Smallest cells: Mycoplasmas (0.3 µm in length).
Largest isolated single cell: Egg of ostrich.
Longest cells: E.g., Nerve cell.
Size of bacteria: 3 to 5 µm (Typical: 1 to 2 µm).
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 of two types: Prokaryotic cells and Eukaryotic cells.
