> Cell sizes are not fixed, however, even within a single species. Cells often swell as they increase their production of proteins and metabolites in preparation for division. This is in line with biology’s only rule: namely, there are exceptions to every rule!
> Case in point: a giant bacterium called Thiomargarita magnifica can extend about one centimeter in length, so large that it can be seen by the naked eye. It does so by breaking the surface area-to-volume rule, filling between 65–80 percent of its internal volume with an empty vacuole. In other words, it pushes most of its molecules to the cell periphery, thus shortening diffusion distances.
There is also a captioned image of bubble algae in the post.
Those still seem kind of small? Why not the size of an mature olive tree for example? I'm guessing the article may answer this, haven't gotten that far yet.
These both feature large central vacuoles, lending support the thesis of the article that the cubic growth in volume outstrips the quadratic increase in surface area for transferring nutrients and waste across the cell membrane.
Granted, they are grouped both in Thiomargarita. 2cm is pretty gigantic. What I always found more interesting was that they don't merely have just one genome.
I never bought into the egg thing. There’s clearly a distinct cell in the center that’s going to divide and grow inside the egg. The egg itself isn’t undergoing mitosis.
Nitpick maybe, but I don't think oocytes are the largest cells, it pretty much has to be some sort of neuron. A sensory neuron for eg. someplace in the foot will be almost as long as the person is tall, and even if the neuron is extremely thin, it's gotta beat the oocyte for volume.
"The allocation of all metabolic resources to maintenance purposes limits the size of the smallest prokaryotes and largest unicellular eukaryotes, whereas an inability to meet the ever-increasing biosynthesis rates limits the largest prokaryotes and smallest unicellular eukaryotes. Metabolic constraints for larger eukaryotes are relieved by alternative reproductive strategies and multicellularity."
I've recently gotten into microscopy as a hobby and comparing the relative size of microbes is really interesting. There are entire animals (tardigrades for one) which can be smaller than some single celled organisms.
There are even single celled organisms which will prey upon and eat multicellular animals.
I feel like keeping the amount of molecules the same within the simulation needs to be justified.
How would it look like if the average amount of molecule was the same across a um?
Perhaps cells are small in the first place is for efficiency. It's more efficient to perform a set of tasks with trillions of these cells in unison than one big blob.
Aside from the anthropocentric view that cells are relatively small because we are made of many of them, the increases in size of lifeforms past that of individual cells is a matter of exceeding thermodynamic and informational limits. I highly recommend the book _The Vital Question_ as an intro to the systemic view of this kind of biological complexification
On Being the Right Size turned 100 this year. It's not entirely the same topic as this essay, but this reminded me of it and it's a pretty famous short essay that's worth reading if you haven't seen it.
Nice article! There is another interesting perspective:
Anything selfreplicating kinda needs to be as small as possible (compared to the smallest internal mechanisms required), otherwise the replication time grows out of control:
Consider a 3D printer that can fully selfreplicate by depositing individual molecules: If this was the size of a regular printer, the replication time would be hopelessly long (>billion years even if it could deposit billions of atoms/s).
This applies somewhat universally, and is one of the reason why our current industrial tech is so unsuitable for selfreplication: Any "printing" like process (books, metal stamping, lithography) requires internal features that are much smaller than the output it produces.
FWIW I wrote a paper on nutrient-limited growth rates of cells and how that depends on their shape. one of the interesting findings was that elongated cells can grow exponentially quickly (as observed) while spheres quickly max out.
All life started from procaryotic cells. The step from macromolecules to the first cell cannot be big, otherwise it could not happen spontaneously. On the other side, it must be big enough so that the cell have enough flexibility and functionality to support complex life.
That is, the cell is small enough in order to be produced directly by molecules but large enough in order to be a full living organism (reproduction, metabolism etc). This sweet spot seems to be the cell size we observe.
Later in evolution the size disparity grew because a procaryotic cell swallowed another one to become an eucaryotic and the eucaryotic ones specialized even further.
38 comments
[ 4.0 ms ] story [ 74.2 ms ] threadLargest eukaryote:
https://en.wikipedia.org/wiki/Valonia_ventricosa
largest prokaryote:
https://en.wikipedia.org/wiki/Thiomargarita_namibiensis
> Case in point: a giant bacterium called Thiomargarita magnifica can extend about one centimeter in length, so large that it can be seen by the naked eye. It does so by breaking the surface area-to-volume rule, filling between 65–80 percent of its internal volume with an empty vacuole. In other words, it pushes most of its molecules to the cell periphery, thus shortening diffusion distances.
There is also a captioned image of bubble algae in the post.
Actually the wikipedia article states:
"It is the second largest bacterium ever discovered"
> The largest T. magnifica cell Volland found was 2 centimeters tall
https://www.science.org/content/article/largest-bacterium-ev...
Granted, they are grouped both in Thiomargarita. 2cm is pretty gigantic. What I always found more interesting was that they don't merely have just one genome.
https://en.wikipedia.org/wiki/Valonia_ventricosa
https://en.wikipedia.org/wiki/Acetabularia
Yeah. That's probably it. Really, it probably is the right answer.
"The allocation of all metabolic resources to maintenance purposes limits the size of the smallest prokaryotes and largest unicellular eukaryotes, whereas an inability to meet the ever-increasing biosynthesis rates limits the largest prokaryotes and smallest unicellular eukaryotes. Metabolic constraints for larger eukaryotes are relieved by alternative reproductive strategies and multicellularity."
[0] https://www.princeton.edu/news/2013/10/24/gravity-plays-role...
There are even single celled organisms which will prey upon and eat multicellular animals.
Why do our bodies constrain everything else? Sure, WE are big in cell-units, but why are cell-units in the size range they are?
https://teaching.hkaiser.org/fall2025/csc7103/course/papers/... (PDF 50 KB, 5 pages essay + 3 pages commentary)
Thanks for the good work
Anything selfreplicating kinda needs to be as small as possible (compared to the smallest internal mechanisms required), otherwise the replication time grows out of control: Consider a 3D printer that can fully selfreplicate by depositing individual molecules: If this was the size of a regular printer, the replication time would be hopelessly long (>billion years even if it could deposit billions of atoms/s).
This applies somewhat universally, and is one of the reason why our current industrial tech is so unsuitable for selfreplication: Any "printing" like process (books, metal stamping, lithography) requires internal features that are much smaller than the output it produces.
Also : as usual, lots of HN type nitpicking in the comments, most missing the main story.
https://arxiv.org/abs/1312.0674
That is, the cell is small enough in order to be produced directly by molecules but large enough in order to be a full living organism (reproduction, metabolism etc). This sweet spot seems to be the cell size we observe.
Later in evolution the size disparity grew because a procaryotic cell swallowed another one to become an eucaryotic and the eucaryotic ones specialized even further.