Cell Structure and Micro-organisms
- Cell
- Cells are the basic structural units and the building blocks of all living organisms.
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Discovery of the Cell
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Cell was discovered by Robert Hooke in 1665 after observing a piece of cork under a magnifying device.
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Robert Hooke coined the term “cell”.
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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.
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Number of Cells
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Organisms made of only a single cell are called unicellular organisms.
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For example: Amoeba and Paramecium
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Single cell in these organisms performs all the basic functions such as digestion, respiration, excretion, etc.
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Organisms made up of more than one cells are called multicellular organisms.
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For example: Humans, cow, rose, etc.
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In these organisms, the cells show division of labour as particular set of cells are involved in performing a specific body function.
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Shape of the Cells
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Most of the cells have a definite shape.
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Some cells such as that in Amoeba have no definite shape.
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The human red blood cell (RBC) is spherical-shaped.
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The muscle cells in humans are spindle-shaped.
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The human nerve cells have elongated branched structure.
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In plants and bacteria, the cell is enclosed in a protective covering called cell wall, which gives shape and rigidity to the cells.
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Size of the Cells
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The smallest cell is 0.1 to …
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