Q.What is the main difference between intussusception and accretion?

Growth in Living Organisms

Think about a puppy you've seen grow into a full-sized dog. Or a sapling that becomes a mango tree. That increase in size — the puppy getting heavier, the tree getting taller — is what we call growth. But here's the key: growth isn't just about getting bigger. It's about how you get bigger.

A mountain also "grows" over millions of years — dust and rock pile up on its surface. A sand dune grows when wind blows more sand onto it. So what's the difference between the puppy and the mountain?

The difference is where the growth comes from.

The Intuition: Inside vs. Outside

In a living organism, growth happens from the inside. The puppy doesn't grow because someone glues fur onto it. It grows because its own cells divide, make more cells, and those new cells get larger. Food is broken down, and the materials are used to build new living tissue — from within.

In a non-living thing like a mountain, growth happens from the outside. Particles of dust, rock, or sand accumulate on its surface. Nothing inside the mountain is dividing or building. It's just stuff sticking to stuff.

The Precise Statement

Growth in living organisms is an irreversible increase in:

1. Mass — the total amount of living material (protoplasm) increases.
2. Number of cells — through the process of cell division.

And crucially, this increase is intrinsic — it is driven by the organism's own metabolic processes (like nutrition and respiration). The organism uses energy to build itself from the inside.

A Common Confusion …