includes basics about fundamental unit of life including cell division and division of labour

2. • Cells were first discovered by Robert Hooke in 1665. He observed the cells in a cork slice with
the help of a primitive microscope.
• Leeuwenhoek (1674), with the improved microscope, discovered the free living cells in pond
water for the first time.
• It was Robert Brown in 1831 who discovered the nucleus in the cell.
• Leeuwenhoek (1674), with the improved microscope, discovered the free living cells in pond
water for the first time.
• Purkinje in 1839 coined the term ‘protoplasm’ for the fluid substance of the cell.
• The cell theory, that all the plants and animals are composed of cells and that the cell is the
basic unit of life, was presented by two biologists, Schleiden (1838) and Schwann (1839). The
cell theory was further expanded by Virchow (1855) by suggesting that all cells arise from pre-
existing cells.

3.  The invention of magnifying lenses led
to the discovery of the microscopic
world.
 Microscope are high resolution
instruments that are used for observing
fine details of very small objects.
 Cells are too small to be studied by
naked eye, they are studied with the
help of microscope.
 There are two types of microscope-
light microscope and electron
microscope.

4.  Shape and size of cell greatly vary
depending upon the specific functions
they perform.
 Some cell have the ability to change
shape e.g. Amoeba, WBCs, while others
have fixed shape like most cell of plant
and animals.
 In some cases the cell shape could be
more or less fixed and peculiar for a
particular type of cell; for example, nerve
cells have a typical shape.

5.  Smallest Cell – PPLO (Mycoplasma)
 Longest cell in human body- nerve cell
 The smallest prokaryotic cell – diameter of
400nm
 Range of eukarotic cell – 1-100 µm
 Largest cell- Ostrich’s egg ehich about 10,000
times bigger than a mouse cell which has a
diameter of 10 µm)
 The shape of Red blood cell help them in
moving through capillaries and arteries and
veins.
 The spikes on pollen grain grain help it to stick
to pollinating insect or animal
 Axon of nerve cell have thin extension which
help them in transmission of signal.
INTRESTING FACTS ABOUT SHAPE AND SIZE OF CELL
A- Ostrich’s egg
B- mouse cell
PPLO
(Mycoplasma)

6. Cell Organelles cell inclusions
These are the membrane bound
structures in a cell that perform a special
function.
Non living material in the protoplasm
of a cell, such as pigments, granules,
fat droplets.
Bound by membrane Not enclosed by membrane
Perform a unique function in the cell. Formed as a result of functioning of
cell organelles.
Self replicable Not self replicable
Unique biochemical reaction occur inside
them.
Are the end product of the
biochemical process
Cell showing different cell
organelles
Granulocyte with granules of
digesting enzymes ( cell
inclusions)

7. Multicellular organisms are
made up of millions and
trillions of cells. All these cells
perform specific functions. All
the cells specialised for
performing similar functions
are grouped together as
tissues in the body. Hence, a
particular function is carried
out by a group of cells at a
definite place in the body.
Similarly, different functions
are carried out by different
groups of cells in an organism
and this is known as the
division of labour in
multicellular organisms.

9. Significance of cell division can be understood by following points-
1. Cell division is a pre-requisite for the continuity of life and forms the
basis of evolution to various life forms.
2. In unicellular organisms, cell division is the means of asexual
reproduction, which produces two or more new individuals from the
mother cell. The group of such identical individuals is known as clone.
3. In multi-cellular organisms, life starts from a single cell called zygote
(fertilized egg). The zygote transforms into an adult that is composed of
millions of cells formed by successive divisions.
4. Cell division is the basis of repair and regeneration of old and worn
out tissues.