CELL — STRUCTURE AND FUNCTIONS
Y
ou have already learnt that things These boxes appeared like a honey-
around us are either living or comb. He also noticed that one box was
non-living. Further, you may separated from the other by a wall or
recall that all living organisms carry out partition. Hooke coined the term ‘cell’
certain basic functions. Can you list for each box. What Hooke observed as
these functions? boxes or cells in the cork were actually
Different sets of organs perform the dead cells.
various functions you have listed. In this Cells of living organisms could be
chapter, you shall learn about the basic observed only after the discovery of
structural unit of an organ, which is the improved microscopes. Very little was
cell. Cells may be compared to bricks. known about the cell for the next 150
Bricks are assembled to make a building. years after Robert Hooke’s observations.
Similarly, cells are assembled to make Today, we know a lot about cell
the body of every organism. structure and its functions because of
improved microscopes having high
8.1 Discovery of the Cell magnification.
Robert Hooke in 1665 observed slices of
cork under a simple magnifying device.
8.2 The Cell
Cork is a part of the bark of a Both, bricks in a building and cells in
tree. He took thin slices of cork and the living organisms, are b a s i c
observed them under a microscope. He structural units [Fig. 8.2(a), (b)]. The
noticed partitioned boxes or buildings, though built of similar bricks,
compartments in the cork slice (Fig. 8.1). have different designs, shapes and sizes.
Similarly, in the living world, organisms
differ from one another but all are made
up of cells. Cells in the living organisms
are complex living structures unlike
non-living bricks.
A hen’s egg can be seen
easily. Is it a cell or a
Fig. 8.1: Cork cells as observed by group of cells?
Robert Hooke
2022-23
, (a) Brick wall (b) Onion peel
Fig. 8.2 : Brick wall and onion peel
The egg of a hen represents a single Organisms made of more than one
cell and is big enough to be seen by the cell are called multicellular (multi :
unaided eye. many; cellular : cell) organisms. The
number of cells being less in smaller
8.3 Organisms show Variety organisms does not, in any way, affect
in Cell Number, Shape and the functioning of the organisms. You
Size will be surprised to know that an
How do scientists observe and study the organism with billions of cells begins
living cells? They use microscopes which life as a single cell which is the fertilised
magnify objects. Stains (dyes) are used egg. The fertilised egg cell multiplies and
to colour parts of the cell to study the the number of cells increase as
detailed structure. development proceeds.
There are millions of living Look at Fig 8.3 (a) and (b). Both
organisms. They are of different shapes organisms are made up of a single cell.
and sizes. Their organs also vary in The single-celled organisms are called
shape, size and number of cells. Let us unicellular (uni : one; cellular : cell)
study about some of them.
Number of Cells
Can you guess the number of cells in a
tall tree or in a huge animal like the
elephant? The number runs into
billions and trillions. Human body has
trillions of cells which vary in shapes
and sizes. Different groups of cells
perform a variety of functions.
A billion is a thousand million. A (a) (b)
trillion is a thousand billion.
Fig. 8.3 : (a) Amoeba (b) Paramecium
CELL — STRUCTURE AND FUNCTIONS 91
2022-23
Y
ou have already learnt that things These boxes appeared like a honey-
around us are either living or comb. He also noticed that one box was
non-living. Further, you may separated from the other by a wall or
recall that all living organisms carry out partition. Hooke coined the term ‘cell’
certain basic functions. Can you list for each box. What Hooke observed as
these functions? boxes or cells in the cork were actually
Different sets of organs perform the dead cells.
various functions you have listed. In this Cells of living organisms could be
chapter, you shall learn about the basic observed only after the discovery of
structural unit of an organ, which is the improved microscopes. Very little was
cell. Cells may be compared to bricks. known about the cell for the next 150
Bricks are assembled to make a building. years after Robert Hooke’s observations.
Similarly, cells are assembled to make Today, we know a lot about cell
the body of every organism. structure and its functions because of
improved microscopes having high
8.1 Discovery of the Cell magnification.
Robert Hooke in 1665 observed slices of
cork under a simple magnifying device.
8.2 The Cell
Cork is a part of the bark of a Both, bricks in a building and cells in
tree. He took thin slices of cork and the living organisms, are b a s i c
observed them under a microscope. He structural units [Fig. 8.2(a), (b)]. The
noticed partitioned boxes or buildings, though built of similar bricks,
compartments in the cork slice (Fig. 8.1). have different designs, shapes and sizes.
Similarly, in the living world, organisms
differ from one another but all are made
up of cells. Cells in the living organisms
are complex living structures unlike
non-living bricks.
A hen’s egg can be seen
easily. Is it a cell or a
Fig. 8.1: Cork cells as observed by group of cells?
Robert Hooke
2022-23
, (a) Brick wall (b) Onion peel
Fig. 8.2 : Brick wall and onion peel
The egg of a hen represents a single Organisms made of more than one
cell and is big enough to be seen by the cell are called multicellular (multi :
unaided eye. many; cellular : cell) organisms. The
number of cells being less in smaller
8.3 Organisms show Variety organisms does not, in any way, affect
in Cell Number, Shape and the functioning of the organisms. You
Size will be surprised to know that an
How do scientists observe and study the organism with billions of cells begins
living cells? They use microscopes which life as a single cell which is the fertilised
magnify objects. Stains (dyes) are used egg. The fertilised egg cell multiplies and
to colour parts of the cell to study the the number of cells increase as
detailed structure. development proceeds.
There are millions of living Look at Fig 8.3 (a) and (b). Both
organisms. They are of different shapes organisms are made up of a single cell.
and sizes. Their organs also vary in The single-celled organisms are called
shape, size and number of cells. Let us unicellular (uni : one; cellular : cell)
study about some of them.
Number of Cells
Can you guess the number of cells in a
tall tree or in a huge animal like the
elephant? The number runs into
billions and trillions. Human body has
trillions of cells which vary in shapes
and sizes. Different groups of cells
perform a variety of functions.
A billion is a thousand million. A (a) (b)
trillion is a thousand billion.
Fig. 8.3 : (a) Amoeba (b) Paramecium
CELL — STRUCTURE AND FUNCTIONS 91
2022-23
