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. Do subscribe for more videos on biology.

If you have any questions ask me in the comments below