Introduction to cells - Class 9 Biology - Science Video Lecture

Cells- The fundamental Unit of life If you
remember, in our previous session we have
seen the basic difference between a living
and a non- living thing and some of the characteristics
shown by living organisms.
So today we will be looking at the 1st characteristic
in detail i.e the composition of an organism
The trees in the forest the fish in the riverthe
birds in the sky the worm in the soilthe tiger
in the jungle the cactus in the desert your
class mate in fact any living thing on this
planet is made up of cells which are known
to be the building blocks of a living thing.
Many many cells come together to form a living
organism.
Besides this, some organisms like bacteria
are made up of only one cell.
One celled organism is all together an individual
itself which can perform all the functions
like any other multi-cellular organism.
Every living being performs various functions
during its entire lifespan like respiration,
digestion, excretion, reproduction etc. the
body has specific organs to carry out these
functions.
These organs are made up of various types
of tissues; and tissues are nothing but a
group of cells.
So in short we can say that the human body
is composed of many cells.Just as bricks form
the important part of a building, cells make
up an organism.
So we can say that cells are the basic fundamental
unit of life.
In 1665, Robert Hooke discovered cells.
He observed dead cells within the cork of
the bark of a tree using an old basic microscope.
He observed empty spaces contained by a wall
and named them cells because they resembled
small compartments.
So we can say that what Robert Hooke observed
looked something similar to a honeycomb structure.
We shall take a look at some features of a
cell.
So lets get started.
No. of cells:
Based on the no. of cells an organism can
either be unicellular or multi cellular.
As the word suggests Uni- is one
cell and multi is many cells.
Shape of a cell:
Cells are of various shapes.
Majority of them are round, spherical and
elongated.
But you know what gives a cell its shape..???
Just like a room gets its shape from its walls
a cell gets its shape from a cell membrane
which is the outer covering of the cell.
Soooo talking about shape of cells u know
a unicellular organism named amoeba has no
definite shape it is irregular and it keeps
changing its shape.
In multi-cellular organisms, cells are of
different shapes.
Like for eg.
A nerve cell is long and branched in structure
while a red blood cell (rbc) is spherical
and concave.
Size of a cell:
Cells are very tiny in size and are not visible
by the eye.
Hence to view them we use a microscope which
is an instrument that magnifies and enlarges
the image of a cell.
So did you all know that A smallest cell is
0.1 to 0.5 micrometer which is of a bacteria
while the largest cell is 170 mm x 130 mm
in size which is the egg of an ostrich.
You must know that the Size of a cell is based
on the function it performs and not on the
size of an organism.
sooo..
The nerve cell in an elephant and a rat will
be of the same size.
A cell has many parts and it contains components
which help in the proper functioning of the
cell.
We will have a look at them in detail in our
next video.
Till then why dont you all try a small exercise
Exercise: try listing all the various types
of cells found in a human.
Until now we have been saying that biology
is all about study of life but life is composed
of many many cells which come together to
form a living organism.
Our planet consists of a vast number of creatures;
some may be formed of just one cell like we
have seen in an amoeba while others are multi-cellular
No of cells can vary depending on the size
of an organism an elephant will obviously
have more no of cells compared to a rat but
the size of a cell will remain the same as
we have seen previously.
Also cells have a property of regeneration.
Imagine you have got a wound on your knee
and your skin cells are damaged.
But your body has a tendency to regenerate
those cells on its own.
This is
the most fascinating property
of cells.
So till
the
next video follow your curiosity.
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If you have any questions ask me in the comments
below