Biology · The Living World · NEET
No. NCERT is very clear: growth cannot be taken as a defining property of life. Two reasons. First, non-living things like mountains, boulders and sand mounds also increase in size, so growth is not unique to living things. Second, a dead organism does not grow at all. So even living things stop growing once they die. Because of these two problems, growth is NOT a defining feature. The only defining property of life is METABOLISM. Remember this for NEET: growth is a characteristic you can observe, but not a defining one.
Intrinsic means from the inside. Extrinsic means from the outside. Living things show intrinsic growth: new cells are made inside the body by cell division, and these new cells are added throughout the body, so the whole organism gets bigger from within. Non-living things show extrinsic growth: extra material simply gets piled on the OUTER surface. A mountain grows when more rock and soil settle on top of it. So the key line for NEET is: living things grow from inside by adding cells, non-living things grow from outside by adding material on the surface.
Yes, they do increase in size, but in a different way. A mountain gets taller when more sediment and rock deposit on its surface. A crystal gets bigger when more molecules stick to its outer faces from the surrounding solution. Sand dunes grow when wind piles more sand on them. But in every case the growth is only by ACCUMULATION on the outer surface, not by adding material from the inside. This is why we call it extrinsic (external) growth. It looks like growth but is completely different from how a living organism grows.
No, a dead organism does not grow. This is a very important NEET point. If growth were the true test of being alive, then a dead body should still grow, but it does not. This proves that growth by itself cannot define whether something is living. It is one of the two reasons NCERT gives for rejecting growth as a defining property (the other reason is that non-living things also increase in size).
In unicellular organisms (like Amoeba or bacteria), growth means an increase in cell number by cell division. But the same cell division also produces new individuals, which is reproduction. So in a unicellular organism, growth and reproduction are the SAME event. NCERT calls this being synonymous. This exact point was tested in NEET 2016 (statement: In unicellular organisms, reproduction is synonymous with growth). In multicellular organisms, growth (adding cells to the same body) and reproduction (making new individuals) are two separate processes.
NCERT says growth and development in living things are controlled by two kinds of factors. Intrinsic factors are internal, like genes (genetic control) and internal chemicals such as plant growth regulators or hormones. Extrinsic factors are external, like light, temperature, water, oxygen and nutrition. Do not confuse these two uses of the word extrinsic: here extrinsic FACTORS mean external conditions that control growth, while extrinsic GROWTH earlier meant growth by adding material on the outside surface (which is what non-living things do).
Study the four statements (A-D) given below and select the two correct ones out of them: A. Definition of biological species was given by Ernst Mayr. B. Photoperiod does not affect reproduction in plants. C. Binomial nomenclature system was given by R.H. Whittaker. D. In unicellular organisms, reproduction is synonymous with growth.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. Non-living things also increase in size and dead organisms do not grow, so growth cannot define life. Only metabolism is a defining property.
Intrinsic growth is growth from the inside of the body by cell division, seen in all living organisms.
Extrinsic growth is an increase in size by adding material only on the outer surface, seen in non-living things like mountains and crystals.
A mountain, a sand dune or a crystal. All of them get bigger by accumulation of material on the outside, not from within.
Because a single cell divides to increase its number, and that same division also makes new individuals, so both happen in one event. NEET 2016 tested this exact fact.
