The number of cells in the body varies with different
organisms. In some lower forms of life (Example: Euglena, Amoeba)
The body is formed of a single cell;
these organism are described as unicellular. In a unicellular
organism, all life
activities are carried out by itself with its internal structures. The
intracellular structures are called the organelles.
In the vast majority of plants and animals, the body is
made up of numerous cells. They are called multicellular organisms. A multicellular organism is actually an aggregation of
cells. Here a group of cells functions in a same way to form a tissue or an organ
(Example: Xylem vessels, cork cells, cells in the skin). Multicellular
organisms have a great capacity to survive than unicellular organisms.
Unicellular Organism vs Multicellular Organism
Unicellular Organism
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Multicellular Organism
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The body of the
organism is composed of a single cell.
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The body of the
organism is composed of numerous cells.
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Division of
labour is at the organelle level.
It gives a low level of operation efficiency. |
Division of
labour may be at cellular, tissue, organ and organ system level.
It gives high degree of operational efficiency. |
A single cell
carries out all the life processes.
 |
Different cells
are specialized to perform different functions.
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The cell body is
exposed to the environment on all sides.
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Only outer cells
are specialized to face the environment. Inner cells are devoted to other
functions.
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A cell body
cannot attain a large size because of the limit imposed by surface area to volume
ratio.
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A multicellular
body can attain a large size increasing the number of small cells.
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An injury of the
cell can cause death of the organism.
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Injury or death
of some cells does not affect the organism as the same can be replaced by new
one.
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Power of
division is not lost.
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Certain
specialised cells lose power of division.
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A well marked
capacity of regeneration is present.
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The capacity of
regeneration decreases with increasing specialisation.
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The cells has
the same role for itself and the organism.
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Cells have
double role. One for themselves and other for the organism.
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Life span is
short due to heavy load of work.
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Life span is
ling due to limited load of work for each cell type.
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