Which among the following best describes the word “Growth” in living organisms?

The correct option is: Increase in mass due to internally cell division and increase in number due to replication are twin characteristic of growth.

Understanding Growth in Living Organisms:
In biology, growth is defined as an irreversible, permanent increase in the size, mass, or volume of an organism, its organs, or individual cells. To analyze and measure this process, scientists look at two key parameters, which are widely referred to as the twin characteristics of growth:
1. Increase in mass: Living organisms grow from the inside out (intrinsic growth) by synthesizing new cellular materials, which leads to an increase in their overall biomass.
2. Increase in number: Through cell division and replication, the number of cells increases. In multicellular organisms, this increases the size of the body, while in unicellular organisms, it increases the number of individuals in a population.

Why the Other Options are Incorrect:
- "Increase in mass either due to accumulation or due to changes that body undergoes internally": External accumulation of matter (like sand forming a dune or dust gathering on an object) is a form of growth seen in non-living things. Living growth must occur strictly from within.
- "All living organisms grow throughout their life": This is not true for all organisms. While plants grow continuously throughout their lifespan (indeterminate growth), animals only grow up to a certain age (determinate growth).
- "Growth is a sufficient characteristic to determine whether an organism is living or non-living": Since non-living objects can increase in mass via surface accumulation, growth by itself is not a defining or sufficient characteristic of life. Intrinsic growth must be coupled with other life processes to define a living organism.