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Name : Prasad Annasab Khot
Class : VIII , House : KH ,
Section : B , Roll no : 6781
Subject : Biology
PPT of cell chapter
Discovery of the cell
In 1665 a person named ROBERT HOOKE discovered
the cell.
Robert Hooke ;
One day he was observing slices of cork under a
microscope . He noticed partitioned boxes /
compartments in cork slice.
Cell observed by Robert Hooke
The boxes appeared like a honey comb.
Hooke coined the term ‘cell’ for each box. What
Hooke observed as cells in the cork were actually dead
cells.
Cells of living organisms could be observed only after
discovery of improved microscopes.
Microscope:
The cell
The basic building blocks of all living things is called
sell.
Human body is composed of trillions of cells.
They provide structure for the body, take in
nutrients from food, convert those nutrients into
energy, and carry out specialized functions.
Plant cell:
Animal cell:
The egg of a hen represents a single cell and is big
enough to be seen by the unaided eye.
egg:
Organisms show variety in cell
number, shape and size
Scientists study the cell by staining them and
observing them under microscope.
There are millions of living organisms and they are of
different shapes and size in addition to that their
organs also very in shape, size and number of cells.
Photo of animals :
Human body has trillions of cells which vary in shapes
and sizes.
Different groups of cells perform a variety of function.
Organisms made of more than one cell are called
multicellular organisms.
An organism begins life as a single cell which is the
fertilized egg.
Image of fertilized egg:
The fertilized egg cell multiplies and number of cells
increase as development proceeds.
The single celled organisms are called unicellular
organisms.
Amoeba , paramecium are some examples of it
Photo of amoeba and paramecium :
A single celled organism performs all the necessary
function that multicellular organisms perform.
A single celled organism like amoeba, captures and
digests food, respires, excretes, grows and
reproduces.
Similar functions in multicellular organisms are carried
out by groups of specialized cells forming different
tissues.
Amoeba has no definite shape, unlike other
organisms. It keeps on changing its shape.
Pseudopodium: a temporary protrusion of the surface
of an amoeboid cell for movement and feeding.
Image of pseudopodia:
A white blood cell (WBC) in human blood is another
example of single cell, which can change its shape.
Generally cells are round, spherical or elongated.
Components of the cell are enclosed in a membrane.
This membrane provides shape to the cell of plants
and animals.
Cell wall is an additional covering over the cell
membrane of plant cell.
It gives shape and rigidity to these cells
The smallest cell is 0.1 to 0.5 micrometer in bacteria
and the largest cell measuring 170 mm × 130 mm, is
the egg of ostrich.
Image of smallest and largest cell :
Size of the cells has no relation with the size of the
body of the animal or plant.
The size of cell is related to its function.
Cell structure and function
Each organ is made up of smaller parts called tissues.
A tissue is a group of similar cells performing a specific
function.
A tissue
