The Fundamental Unit of Life – Cell & Cell Theory (Part -1)

Discovery of Cell

• While examining a thin slice of cork in the 1665, Robert Hooke discovered Cell. He observed that the cork resembled to the structure of a honeycomb consisting of many little compartments.
• Hooke named these compartments as “Cell’s”. Cell is a Latin word for “a little room”.
• The invention of magnifying lenses led to the discovery of the microscopic world.

Discoverers & Discoveries

• Purkinje –  Protoplasam
• Robert Brown – Nucleus
• Schleiden & Schwann – Cell Theory [(i)All organisms have cell (ii) Cell is the basic unit of life]
• Virchow – All cells arise from pre-existing cells.
• Leeuwenhoek – First Microscope
• Electron microscope was discovered in 1940.

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 Cell

• Cell is defined as the basic structural and functional unit of life/living organism, i.e. the fundamental unit of life.
• Cells are the building blocks of Life, together they form a big structure.

Classification of Organisms in terms of No. of Cells in them

• All organisms are made up of cells. However there are also single cells that live on their own.
• Organism with a single cell ⇒ Unicellular Organism
• Organism with more than one (multiple) cell ⇒ Multicellular Organism.
• Unicellular Organisms → Amoeba, Paramecium,  Chamydomonas
• Multicellular Organisms → Fungi, Plants, Animals

Cell Theory

• The cell theory proposed by Schleiden & Schwann states that :-
  1. All living Organisms are composed of Cells.
  2. Cell is the basic unit of Life.
• The cell theory was further expanded by Virchow by suggesting that :-
  1. All living cells arise from pre-existing cells.
• Every multicellular organism has come from a single cell.
  1. Cells divide to produce cells of their own kind, all cell’s thus came from pre-existing cells.

Division of Labour in Cell’s

• All multicellular  organisms show division of labour i.e. different parts perform different functions.
• Different cells perform different tasks.
• In fact every cell show division of labour, its different cell organelles perform different functions, thus they constitute the building blocks of life.
• Cells perform all the functions in an organism. Therefore, Cell is the basic functional unit of life.

• A GROUP OF CELL’S performing similar functions » Tissue
• A GROUP OF TISSUE’s performing similar functions » Organ
• GROUP OF ORGANS performing similar functions » Organ System
• DIFFERENT ORGAN SYSTEM working together » Organism

Shape of Cells

• The shape & size of the cell’s are related to the specific function’s they perform.
• Amoeba is a cell that can change its shape(pseudopodia).
• The flexibility of the cell membrane in  amoeba enables the cell to engulf in food and other materials from its external environment.