Hello Valji Solanki,

Increase in mass and increase in number of individuals are the twin characteristics of growth.

Growth is one of the characteristics of living. All living things grow. We see plants and animals growing in size. In plants, growth is till death. But, it is upto a certain age in animals. However, some of the cell divide to replace the existing torn out or injured cells.

We also see mountains and rivers grow in size. Don't You? Shall we consider them as living?

No, we don't consider them as living. It is because the growth in animals and plants and growth in mountains have something different. That is, the growth in animals and plants is from inside due to increase in cell number whereas growth in mountains or increase in their mass is due to accumulation of materials like soil, rock or sand on its surface.

All living beings reproduce to keep existing on Earth. Some of them reproduces sexually while some reproduce asexually. Reproduction refers to the production of progeny who are almost similar to parents. These progeny possesses features more or less similar to their parents.

Growth is equivalent to increase in number of cells. So, we consider animals growing even after when their body size stops increasing. In general, their growth stops. Growth happens as number of number of cells increase to replace the lost or damaged cells as growth is equivalent to increase in number of cells. Hence, the increase in size and increase in number of organisms of any species is called twin characteristics of growth.

Hope this will help you!