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Cell Structure and Micro-organisms

  • Cell
    • Cells are the basic structural units and the building blocks of all living organisms.
  • Discovery of the Cell

  • Cell was discovered by Robert Hooke in 1665 after observing a piece of cork under a magnifying device.

  • Robert Hooke coined the term “cell”.

  1. Schleiden and Schwann proposed the cell theory. According to cell theory-

    Cells are the basic structural and functional units of life.

    All living organisms are made up of one or more cells.

    New cells arise from pre-existing cells.

  • Number of Cells

  • Organisms made of only a single cell are called unicellular organisms.

  • For example: Amoeba and Paramecium

  • Single cell in these organisms performs all the basic functions such as digestion, respiration, excretion, etc.

  • Organisms made up of more than one cells are called multicellular organisms.

  • For example: Humans, cow, rose, etc.

  • In these organisms, the cells show division of labour as particular set of cells are involved in performing a specific body function.

  • Shape of the Cells

  • Most of the cells have a definite shape.

  • Some cells such as that in Amoeba have no definite shape.

  • The human red blood cell (RBC) is spherical-shaped.

  • The muscle cells in humans are spindle-shaped.

  • The human nerve cells have elongated branched structure.

  • In plants and bacteria, the cell is enclosed in a protective covering called cell wall, which gives shape and rigidity to the cells.

  • Size of the Cells

  • The smallest cell is 0.1 to …

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