Question

Can growth be considered as a defining feature of all living things without an exception

Answer 1

All living organisms grow. An increase in mass and increase in number of individuals are twin characteristics of growth. A multicellular organism grows by cell division. In plants, this growth by cell division occurs continuously throughout their life span. In animals, this growth is seen only up to a certain age. However, cell division occurs in certain tissues to replace lost cells. Unicellular organisms also grow by cell division. One can easily observe this in an invitro cultures by simply counting the number of cells under the microscope. In a majority of higher ordered animals and plants, growth and reproduction are mutually exclusive events. One must remember that increase in body mass is considered as growth. Non-living objects also grow if we take an increase in body mass as a criterion for growth. Mountains, boulders and sand mounds grow, however this kind of growth exhibited by non-living objects is by the accumulation of material on the surface. In living organisms, growth is from inside. Growth, therefore cannot be taken as a defining property of living organisms. Conditions under which growth can be observed in living organisms have to be explained in order to understand that it is a characteristic of living systems. Dead organism do not grow.