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