Page 90 - Science Class 08

He no ced par oned boxes or compartments Cells in the bodies of all organisms vary in
in the cork slice. number, shape and size as under:

v An organism may have only one cell to
carry out its life-func ons single-handed.
Or it may have several cells that perform all

the life-func ons co-opera ng with one
another. Some single-celled organisms
include amoeba, paramecium, euglena and
bacteria. These organisms are known as
unicellular while those with several cells
are called mul cellular.
Cork cells as observed by Robert Hooke
v The different cells of a mul cellular living
These boxes appeared like a honey-comb.
thing have various shapes in general. They
He also no ced that one box was separated
might be elongated, branched, cuboidal,
from the other by a wall or par on. Hooke
round or columnar.
coined the term ‘cell’ for each box. What
v Cells may be microscopic or small in size.
Hooke observed as boxes or cells in the cork
Muscle-cells in animals and fibre-cells in
were actually dead cells.
plants like jute and hemp are a few
Cells of living organisms could be observed only
cen metres each. A hen’s egg is fairly big
a er the discovery of improved microscopes.
cell while that of an ostrich is the largest
Very li le was known about the cell for the
cell on the earth.
next 150 years a er Robert Hooke’s observ-
The table given below gives the sizes of
a ons. Today, we know a lot about cell
some cells:
structure and its func ons because of improved
microscopes having high magnifica on. No. Cell-Type Size
-6
VARIETY IN CELLS 1. Living red blood cell 4 × 10 m
Having followed that body-cells are to body as 2. Nerve cell 1 meter+
bricks are to building, it is not difficult to 3. Green Algae Chara 10 cm
understand that organisms have cells since life 4. Ostrich egg 170 mm across
began on the earth. These cells were never

studied before the modern age. The reason
was that they are much too small to be seen
with the naked eye. The word cell was coined · Robert Hooke discovered the cell in
by a scien st, called Robert Hooke, in the 17th 1665.
century while observing a cork-slice by a
· In 1674, Leeuwenhoek discovered the
microscope. He observed that spaces in the free cells in the form of bacteria.
cork appeared like the compartments of a
· In 1831, Robert Brown discovered the
honey-comb. So, he gave them the name–cells. nucleus of the cell.

90 Science-8