Cell number, size and shape

We all may have played Lego in our childhood.

This house is made up of lego bricks. Here, brick forms the basic structure of this house.

Similarly, we humans are made up of basic unit called cell.

Cells are the basic structural and functional units of all the living organisms.

But these cells, unlike lego bricks, are able to multiply and increase their number on their own.

In lego, we arrange plastic bricks in different patterns.

And also all the bricks are not similar. They can be of different colours or shapes or sizes in different models.

Similarly, cells are also arranged in different numbers in different organisms.

There are some organisms which are made up of only one single cell and some are made up of many cells.

So, on the basis of the number of cells in the organisms, they are divided into two categories.

The first category is of unicellular organisms, which are made up of a single cell.

Microscopic organisms like bacteria, yeast, amoeba, etc. are all unicellular organisms.

The second category is of multicellular organisms, which are made up of many cells.

The plants and animals which we see in our daily lives and humans are all multicellular in nature.

Just like different shapes of lego bricks, cells are also of different shapes.

Cells come in a variety of shapes which depends upon the function they perform.

Spherical-shaped cells: Human red blood cells are of spherical or disk-shaped.

This specific shape of the cell allows them to hold more of the oxygen and enables the easy flow of them in blood vessels.

Chlamydomonas is a unicellular green alga which is oval in shape.

Cylindrical shaped cells can be seen in Spirogyra.

Some cells such as nerve cells are long to conduct impulse.

Some are rectangular in shape as found in leaves of plants and also in the lining of some human organs.

Muscle cells are long and contractile. This shape enables cells to pull or squeeze the parts.

Amoeboid shaped cells are irregular in shape. White blood cells are examples of amoeboid shaped cells.

Guards cells in stomata are bean-shaped, specialised cells for gaseous exchange. The gap between the cells form the stomatal opening and the shape enables the opening and closing of the stomata.

There are some cells which have some unique shapes.

Let us see few such cells and try to learn about them.

Paramecium, a single cell organism, is known as ‘slipper-shaped animalcule’ as it has a body whose shape is similar to a slipper.

Few cells are spindle-shaped and have a wider central part which tapers towards the ends.

An example of spindle-shaped cells is smooth muscle cells in our body which are found in organs like the stomach, bladder, etc.

Cells not only have different shapes but also different sizes.

Let’s have a look at the different sizes of the cells.

In different models of legos, different sizes of bricks can be found. Similarly, cells are also of different sizes.

Most of the cells are very small in size. They are so small that we can not see them with our naked eyes.

We need magnifying instruments like a microscope to see them.

Example of the smallest cells are the bacteria whose size varies from 0.2 to 5 micrometres.

But there are some cells which are so big that we can easily see them. The ostrich eggs are the largest of all cells.

The longest cell found is the cell of nervous tissue - the nerve cell; it has a length of approx. 3 metres.

Revision

All living organisms are made up of cells.

There is a large variation in the size, shape and number of cells.

On the basis of cell numbers, organisms can be unicellular or multicellular.

Cells come in different shapes like oval, cuboid, rectangular, cylindrical, irregular shape, etc.

There is a large variation found in the size of the cells. Cell size can vary from a few micrometres to some metres.

The end