Who proposed what in the cell theory, is Virchow's part original, and sizes of smallest and largest cells?
Aarav Kulkarni11th Sample
22 Aug 2026 · 1 min read
I'm making my third checklist for Cell: The Unit of Life and the opening pages are all names and numbers, which is just the kind of thing I fear forgetting.
Cell theory: Schleiden (botanist) and Schwann (zoologist) said all living things are made of cells and the cell is the basic unit. Then Virchow said "new cells arise from pre-existing cells". Is that second part part of the original statement or did it come later? NCERT calls it "modified". Also, is there any exception to the cell theory? A friend said viruses.
Sizes: the smallest cell is Mycoplasma at 0.3 µm? Bacteria are 3 to 5 µm. Human RBC is around 7 µm in diameter. Largest isolated single cell is an ostrich egg. And the longest cell is a nerve cell. Is it correct?
Also NCERT lists shapes: disc-like, polygonal, columnar, cuboid, thread-like, or even irregular. I want to make sure I get the correct examples, like which cell is amoeboid.
7 answers & replies
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[+][–]Farhan ShaikhDropperSample· 1mo ago
Sizes are right. Add that Mycoplasma is also called PPLO (pleuro pneumonia-like organisms), about 0.3 µm, and it's the smallest cell. Largest isolated single cell: ostrich egg. Nerve cells are among the longest. Human RBC ~7 µm diameter. Bacteria 3 to 5 µm. Order small to large among cells: Mycoplasma, bacteria, human RBC, and way up there the ostrich egg. (Viruses are even smaller but they aren't cells.)
[+][–]Pooja Iyer12thSample· 1mo ago
Cell theory credit: Schleiden was a zoologist who looked at animals and Schwann was a botanist who looked at plants, and then both put it together. Virchow was also part of the original statement, they all proposed the full theory together.
[+][–]Zoya Khan12thSample· 1mo ago
Pooja, I think it's reversed. Schleiden was the botanist (German botanist, studied plants), Schwann the zoologist (studied animals). In 1838-39 they proposed that all plants and animals are composed of cells and cells are the basic unit of life. Later, Virchow (1855) explained that cells divide and new cells are formed from pre-existing cells (Omnis cellula-e cellula), and that modified the theory. That's why NCERT calls it the "modified" cell theory. So Virchow is the later addition and not part of the first statement.
[+][–]Aarav Kulkarni11thSample· 1mo agoAuthor
Thanks zoya! So Schleiden = plant, Schwann = animal, and Virchow came later, and the Latin phrase is the key. I will put it on a card.
[+][–]Pooja Iyer12thSample· 1mo ago
yep, I swapped them 🙈 sorry aarav, I wrote that too fast. Zoya is right.
[+][–]Ishita GoyalDropperSample· 1mo ago
Exceptions: viruses are acellular, they don't have a cell structure of their own (no cytoplasm and organelles) and they only multiply inside a living host cell, so they're usually listed as the exception to the cell theory, though NCERT's main point is about cells in all living organisms. For exam answers: "viruses" if it's asked as an exception, but not a living cell. Another famous question: "Cell theory states that all organisms are made of cells and all cells arise from pre-existing cells".
[+][–]Mehak AroraDropperSample· 1mo ago
Shapes are connected to function. RBCs are disc-like (biconcave actually), which maximises surface for gas exchange, white blood cells are amoeboid so they change shape, which lets them squeeze through capillary walls. Columnar cells in the intestine line the lumen, a nerve cell is long and branched to carry impulses. Tube-like cells are in the xylem in plants. That's how I connected shape to job, so I didn't have to memorise.
