All the living organisms need nutrients,gases,liquids etc., for growth and maintenance of the body.

All the organisms would need to send these materials to all parts of their body whether they are unicellular organisms or multicellular.

In unicellular organisms these may not have to be transported to longer distances while in multicellular forms have to be sent substances to long distances as far as say over 100 feet for the tallest plant on earth.

In lower organisms like amoeba, hydra etc., all the materials are transported through a simple processes like diffusion, osmosis etc., In higher animals with trillions of cells in their body adopt the method of diffusion and osmosis only for the bulk movement of materials, would takes years.

To avoid delay a separate system is needed to carry the materials much faster and more efficiently.

This specialized system that is developed by organisms is called ‘the circulatory system’.

We eat solids, we drink liquids, and we breathe gases. Do you think that it is possible to transport all the three types of materials, through a single system?

Let us study how this circulation is carried out in our body.

Have you ever observed a doctor holding the wrist of the patient and looking at his watch for a minute? What is that he is trying to find out from the watch and the wrist of the patient? You may wonder to know that he is