Unit of life - The Cell

“What is a cell?” Since childhood, we are taught, “Cell is the structural and functional unit of life”; we just learn it, write in examinations and its all over then! But have we ever wondered  what does it actually mean? I am sure everyone will agree with me that human body is one of the most amazing machinery on this planet. But have you ever wondered what it runs on? Yes..It runs on cells; rather we can say it is made of millions and millions of cells.

Frankly speaking, even I didn’t ponder about it much until I went to high school, where I started gaining interest in Biology; thoughts started popping up my mind....A cell which we can’t be seen by naked eyes can perform thousands of functions without taking rest; really? How is it possible? I was amazed.! Its really hard to believe, what all wonders a cell do but believe me, its fun to know.! In my next few articles, I will discuss about cell - the structure and its functions.

To start with, any living organism on earth is composed of cell. The organism can have one cell, called unicellular (uni meaning 'one' and cellular meaning 'consisting of cell') like bacteria is unicellular or the organism can have millions of cells, called multicellular (multi meaning 'many' and cellular meaning 'consisting of cell') as in case of humans. Be it in bacteria or human, a single cell can perform thousands of biochemical reactions every minute and moreover, also, reproduce itself.

Lets just start with knowing the size of cell. Cells come in many different sizes. The smallest of all cells can be as small as Mycoplasma, a bacterium, which is just a micron short while the big cells can be as long nerve cell in human which can exceed 3 meters in length. The average size of normal human cell varies from 10 to 100 micrometers (i.e; 0.000001 meters).

By now, you might be wondering what about the shapes of the cells? Do all cells look alike? The answer is No. Again, just like the sizes varying, the shapes of the cells also vary as can be seen in the figure below. The shapes vary in bacteria and some bacteria are even classified and given a name depending on the shapes. For example, E.coli, the most common bacteria is rod shaped, amoeba (what students say, the easiest organism to draw ;-)) is irregularly shaped and it changes its shape as it moves. The plant cell are somewhat like cuboid.  In humans, also, there are variety of shapes, like, the cells on the skin are flat; whereas the muscle cells are long and thin and nerve cells are elongated with some projections at its one end.

Different shapes of cell

Why different shapes? The shape of these cells are according to their jobs. Like, the cells of the skin are tightly packed to form a layer so as to protect the underlying tissues. The muscle cells are long and connected to bones for bone’s movements. and the projections of nerve cells helps it to connect to various other cells and transmit some information.

The word “Cell” itself can be an organism (like bacteria) while the cell can be a part of an organism. Before we understand the functions, it is necessary to understand the organization of cells. How the cells are organized to form a multicellular living organism?

So, my next topic will be organization of cell followed by functions of components of cells.

Hope you like this post. Comments or doubts are welcome!