The Cell

All living organism from simplest to most powerful are made of cells. Cells are too small to be seen through naked eyes. It can be seen only with the help of microscope that has high magnification. However there is an exception, a hen’s egg. The egg of a hen is a single cell that can be easily seen through naked eyes.

How cell was discovered?

Robert Hooke, an English scientist, in 1665, observed a very thin slice of cork under his microscope. Cork is a protective outer tissue of bark. Robert Hooke noticed that cork was porous and appeared like a honey comb that is comprised of many tiny square boxes. Hooke coined the termcell for these tiny square boxes.

Basic Organization of Cell

Our body is made up of million and millions of tiny cells. But did you know that all these millions and millions of cell came from just one tiny cell?

The human body begins its development as a single newly fertilized cell. During the development of an individual, this single cell divides and get differentiated to perform specific function. A group of similar cell work together to perform a particular function and is known as tissue. Several tissues are organized to form organ. An organ can serve a variety of essential functions that an organism needs to survive. For example, heart, lungs, kidney, liver etc are all organ. When many organs work together, it is known as organ system. An example of organ system is digestive system. The stomach, small intestine and large intestine are all responsible for breaking down of food. These organ system works together in the body of an organism. Thus, the cells are called basic structural unit of living body.

Number of Cells in Different Organisms

You know that humans, and many plants and animals are made up of a large number of cells. Organisms which are made up of a large number of cells are known as multicellular organisms.

But there are some other organisms, which are made up of only one cell. These organisms are called unicellular organisms. The example includes bacteria, Amoeba etc. In these organisms, a single cell performs all the necessary functions like excretion, respiration, digestion etc.

Shape of the Cells in Different Organisms

All cells do not have a similar shape. The shape of each cell varies. It can be rounded, spherical, or elongated in shape. In some cases, cells may not even have a definite shape.

• Round shaped: Red blood cells are spherical in shape.

• Elongated spindle shaped: Muscle cells are elongated in shape.

• Long and branch shaped: Nerve cells are long and have branches.

• No particular shape: White blood cells and Amoeba do not have a definitive shape; their cells have the ability to change their shape. For example, Amoeba keeps on changing its shape by producing various projections across its cell surface, which is called pseudopodia. These projections help the Amoeba in feeding and moving.

Both plant and animal cells have a cell membrane, which gives shape to the cell.In plants as well as bacteria, a cell wall is present surrounding the cell, which gives shape and rigidity to the cells.

Size of the Cell in Different Organisms

The size of the cell also varies in different organisms. Some cells like eggs of birds can be seen with the naked eye, but some other cells are so small that an electron microscope is required to observe them.

Do You Know? The smallest cell measures around 0.1 to 0.5 micrometer. It is present in bacteria. The largest cell measures around 170× 130 mm, and is the egg of an ostrich The longest cell of the human body is the nerve cell. The smallest cell of the human body is the WBC (lymphocyte).