Q.What structural and functional attributes must a cell have to be called a living cell?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Cell Theory
Before microscopes were good enough to reveal life's inner detail, no one knew that a leaf, a fish and a human being were all built from the same basic material. The cell theory is the great generalisation that finally answered two questions at once: what is every living body made of, and where does every cell come from?
The theory was not the discovery of one person but was assembled and refined over the mid-nineteenth century:
- Matthias Schleiden, a botanist, studied many plants and concluded that all plants are made of different kinds of cells that build up the plant's tissues.
- Theodore Schwann, a zoologist, examined many animal cells, noticed that cells are bounded by a thin outer layer (the plasma membrane), and proposed that the bodies of both animals and plants are made of cells and the products of cells.
- Working together, Schleiden and Schwann formulated the cell theory — but their version had a gap: it did not explain how new cells actually arise.
- Rudolf Virchow closed that gap, showing that cells divide and that every new cell comes from a pre-existing cell — the idea captured in the phrase Omnis cellula-e cellula. This gave the theory its final form.
As understood today, the cell theory rests on two statements:
- All living organisms are composed of cells and the products of cells.
- All cells arise from pre-existing cells. …
To be called a living cell, a cell must be able to exist independently and carry out all the essential functions of life on its own.
- It should be capable of an independent existence, without depending on any other cell to survive.
- It should be able to perform all the essential functions of life by itself. …
A living cell needs the ability to exist independently and to carry out every essential life function by itself, which is exactly what makes the cell the smallest true unit of life.
The evidence for what defines a living cell comes from organisms that exist as a single cell. A unicellular organism demonstrates that one complete cell is genuinely enough to survive on its own, without needing to depend on any other cell. Such an organism manages two things simultaneously: it leads an independent existence, and it carries out all of the essential functions of life entirely by itself. …
Method: Deriving General Attributes From a Concrete Example
Abstract-sounding questions like 'what attributes must a thing have to count as X' are much easier to answer if you anchor your reasoning in a concrete real-world example that already satisfies the definition, rather than trying to reason about the abstract category directly. For 'what makes a cell living,' the natural anchor is a unicellular organism — a single-celled creature that is, indisputably, alive on its own.
Ask yourself: what does that single cell actually have, physically, and what does it actually do, functionally, that together let it survive with no help from any other cell? Splitting your answer into these two buckets — structural attributes (a boundary/membrane, its own genetic material, the internal machinery to make proteins and generate energy) and functional attributes (metabolism, growth, responding to stimuli, reproduction) — is what turns a vague impression ('it can live on its own') into the specific, gradeable list the question is actually asking for. …
- CBSE 2026Set ANNUAL1 markMCQQ.Cell is called the structural and functional unit of life because:(a) All cells have nuclei.(b) All functions of organisms arise from cellular activity.(c) Cells are visible to naked eye.(d) Cells divide only once.
›Reveal solutionSolution
A cell is called the structural and functional unit of life because it is both the smallest self-contained structural building block of a body AND the smallest unit capable of carrying out life's processes (metabolism, growth, response, reproduction) on its own.
Structurally, every tissue, organ, and organism is built up from cells — there is no level of organisation smaller than a cell that is itself alive. Functionally, every life process you can name — respiration, protein synthesis, excitability, division — happens inside cells, using cell organelles. A unicellular organism like Amoeba performs all of life's functions within one single cell, which is direct proof that a cell alone is sufficient to sustain life; in multicellular organisms, these same functions are simply distributed among specialised cells working together, but the functions still originate at the cellular level.
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- CBSE 2026Set ANNUAL1 markMCQQ.According to cell theory, new cells originate from :(a) Fermentation(b) Pre-Existing cells(c) Regeneration of old cells(d) Abiotic synthesis
›Reveal solutionSolution
According to cell theory, every new cell is formed by the division of an already-existing cell.
The cell theory was proposed by Schleiden and Schwann (1838-39), who stated that all plants and animals are composed of cells and that the cell is the basic unit of life. This was later expanded by Rudolf Virchow (1855), who added the crucial idea, summarised in the Latin phrase 'Omnis cellula-e cellula' ('every cell arises from a pre-existing cell'). This means new cells are never formed by spontaneous/abiotic synthesis or fermentation, and are not simply …
- CBSE 2022Set TERM11 markMCQQ.Cell theory was given by(a) A. V. Leeuwenhoek(b) Robert Hooke(c) Schwann & Schleiden(d) Brown & Virchow
›Reveal solutionSolution
The cell theory in its original form was proposed jointly by Schleiden and Schwann.
History of cell theory: Robert Hooke first observed and named 'cells' in cork tissue in 1665 (but these were dead cell walls, not living cells) using a self-designed microscope. Antony van Leeuwenhoek was the first to observe and describe a living cell (in 1674). Building on decades of microscopic observation, Matthias Schleiden (a botanist, 1838) and Theodor Schwann (a zoologist, 1839) together formulated the cell theory, stating that all plants and animals are composed of cells and that the cell is the basic unit of life. …
- CBSE 2022Set ANNUAL1 markMCQQ.___________ is an exception to Cell Theory.(a) Fungi(b) Bacteria(c) Mycoplasma(d) Virus
›Reveal solutionSolution
Viruses lack cellular organisation and cannot multiply independently, which is why they are considered an exception to the Cell Theory.
The Cell Theory (Schleiden, Schwann, and later extended by Virchow) states that:
- All living organisms are composed of cells.
- The cell is the basic structural and functional unit of life.
- All cells arise from pre-existing cells.
Fungi and Bacteria are both truly cellular — bacteria are prokaryotic cells and fungi are eukaryotic cells, so they follow the Cell Theory. Mycoplasma, though the smallest known cellular organism, still possesses a cell membrane and cytoplasm and is cellular. Viruses, in contrast, are non-cellular — they consist only of a nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid), have no cytoplasm, no cell membrane of …
- CBSE 2018Set zoology1 markMCQQ.New cells generate from:(a) Bacterial fermentation(b) Regeneration of old cells(c) Pre-existing cells(d) Abiotic material
›Reveal solutionSolution
New cells generate only from pre-existing cells, by cell division — this is a core part of the Cell Theory and rules out spontaneous generation.
One of the fundamental postulates of the Cell Theory (extended by Rudolf Virchow in 1855) is "Omnis cellula-e cellula" — every cell arises from a pre-existing cell, through the process of cell division (mitosis or meiosis). This directly disproved the earlier idea of spontaneous generation of cells from non-living matter.
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