Biology · Cell: The Unit of Life · NEET
A cell is the smallest living part of any organism. It can take in food, use energy, grow, respond, and make more cells. All living things, from bacteria to humans, are built from cells. Some organisms are made of just one cell (unicellular, like Amoeba) and some are made of many cells (multicellular, like you).
Because it is the smallest thing that is fully alive. NCERT says a cell is the 'fundamental structural and functional unit of all living organisms.' Anything smaller than a complete cell, like a single membrane or a lone organelle, cannot live on its own. So life begins at the cell level, and that is why we call the cell the unit of life.
'Structural unit' means the cell is the building block of the body, the way bricks build a wall. 'Functional unit' means each cell does the jobs of life, like respiration and making proteins. The cell is both at once, so it is the smallest complete unit of both body-building and life-activity.
Antonie van Leeuwenhoek first saw and described a live cell using his simple microscope. Later, Robert Brown discovered the nucleus inside the cell. Do not mix this up: Robert Hooke first saw dead cork cells and gave the name 'cell', but Leeuwenhoek was the first to see a living cell. NEET has trapped students on this exact difference.
Yes. A unicellular organism can do two things: (i) live an independent existence, and (ii) perform all the essential functions of life. Because a single cell can do both, it is alive on its own. This is the whole reason the cell, and not something smaller, is the unit of life.
Mycoplasma (also called PPLO) are the smallest living cells, about 0.3 micrometre in size, and they have no cell wall. They are still complete, working cells, so they are still living. This shows that being small does not stop something from being a full unit of life.
The concept of "Omnis cellula-e cellula" regarding cell division was first proposed by
Cell theory was formulated by ______________.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. A virus is not a cell because it has no cell membrane, no cytoplasm, and cannot perform life functions or reproduce on its own outside a host. Since it is not a complete cell, it is not counted as the unit of life. This point is commonly tested in NEET.
A unicellular organism is made of just one cell that does everything, like Amoeba or bacteria. A multicellular organism is made of many cells that share different jobs, like humans and plants. In both cases the cell is still the basic unit of life.
Because life needs many parts working together inside one boundary: a membrane, genetic material, and machinery to use energy and make proteins. Only a complete cell has all of these together. A single organelle or molecule alone cannot live, so the cell is the smallest living unit.
Robert Brown discovered the nucleus. Robert Hooke coined the word 'cell' after seeing dead cork cells. Antonie van Leeuwenhoek first saw a living cell. NEET often mixes these three names, so memorise who did what.
