Biology · The Living World · NEET
'Living' means a thing shows the special activities of life. NCERT lists these: growth, reproduction, metabolism, cellular organisation, consciousness, and the power to sense and respond to the environment. The first and most basic sign is that all living organisms are made of cells — one cell (unicellular) or many cells (multicellular). If something has none of these features, it is non-living.
Because non-living things can also grow. A mountain, a sand dune, or a crystal grows bigger by adding material from outside. Living things grow from inside (cells increase in number and size), while non-living things grow from outside. So growth alone cannot separate living from non-living. Also, an adult or a dead organism does not grow, but that does not make them non-living just because growth stopped.
Because some living things cannot reproduce but are still fully alive. Mules, sterile worker bees, and many barren couples do not reproduce, yet they are living. So reproduction has exceptions. In unicellular organisms, growth and reproduction are the same thing — when the cell divides, it both grows (in number) and reproduces. This is why growth and reproduction, on their own, are not defining features.
Metabolism. NCERT says metabolism (all the chemical reactions happening inside the body) is the defining feature of all living organisms without exception. No non-living thing shows metabolism. Even a single cell can show metabolism. Cellular organisation is also a defining feature. A key point: isolated metabolic reactions in a test tube are NOT living, but the sum of all reactions inside a body is a sign of life.
No. Machines can move and respond, but they do not have metabolism of their own, they are not made of living cells, and they cannot self-replicate on their own. NCERT stresses that consciousness — the power to sense the environment and respond, and to be aware of oneself — is the defining property of living organisms, especially humans. A machine does not have real self-consciousness or metabolism, so it is non-living.
A living organism is a self-replicating, evolving, self-regulating interactive system that shows metabolism, cellular organisation, and responds to its environment. For a one-word exam answer, metabolism and cellular organisation are defining (no exceptions), while growth and reproduction are characteristics with exceptions. Remember: all defining features together make life, and this connects to the next idea — why metabolism is the only true defining property.
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. The two correct statements are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
NCERT lists growth, reproduction, metabolism, cellular organisation, consciousness, and the ability to sense and respond to the environment. Among these, metabolism and cellular organisation are true defining features (no exceptions), while growth and reproduction are characteristics with exceptions.
Yes. NCERT clearly states metabolism is the defining feature of all living organisms without exception. Non-living things never show metabolism. This is the safest answer for NEET when asked for the defining property of life.
Being made of cells. NCERT says the presence of the cell — the basic unit of life — is what an inanimate thing does not have but a living thing has. Organisms are either unicellular (one cell) or multicellular (many cells).
Yes, but differently. Non-living things (mountains, crystals, sand dunes) grow by adding material on the outside. Living things grow from within, by increasing cell number and cell size. This inside-vs-outside difference is a common NEET trap.
Because all living organisms — from prokaryotes to plants to humans — sense their surroundings and respond to physical, chemical, and biological stimuli. Human beings show self-consciousness, being aware of themselves, which NCERT highlights as the highest form of this property.
