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Why are cells small?
- WorkerBee28474 5mo agoAnother answer is: They're not - at least in some plants: https://en.wikipedia.org/wiki/Valonia_ventricosa https://en.wikipedia.org/wiki/Valonia_ventricosa https://en.wikipedia.org/wiki/Acetabularia https://en.wikipedia.org/wiki/Acetabularia
- chasil 5mo agoNot all are? Largest eukaryote: https://en.wikipedia.org/wiki/Valonia_ventricosa https://en.wikipedia.org/wiki/Valonia_ventricosa largest prokaryote: https://en.wikipedia.org/wiki/Thiomargarita_namibiensis https://en.wikipedia.org/wiki/Thiomargarita_namibiensis
- DaveSchmindel 5mo ago> 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.
- cwmoore 5mo agoInteresting topology. How empty is the vacuole?
- trumpdong 5mo agoempty in terms of normal cell components, apparently it stores relatively huge amounts of nitrates that are a necessary energy source for it
- magicalhippo 5mo agoRather large gas tank: Collected and stored sediment samples were found to have surviving T. namibiensis cells after over two years. The cells had no access to any added sulfide or nitrate during this time. In the surviving cells, there was a notable size decrease. To survive without growing the cells depended on the nutrient stores of the central vacuoles.
- trumpdong 5mo agoIndeed. It says they rely on two different substances which normally don't mix (nitrates and sulfites), presumably because if they were both present at the same time they'd react with each other directly without the bacterium extracting any energy from that. So they live in places that sometimes have one and sometimes the other, and have to store one of them until the other comes along, which can be years. Or that's how I read it.
- vasco 5mo ago> This is in line with biology’s only rule: namely, there are exceptions to every rule! Nice paradox
- embedding-shape 5mo agoThose 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.
- malfist 5mo agoWhen they invade your saltwater aquarium, you won't think they're small. They can get up just slightly larger than a marble
- MagicMoonlight 5mo ago[dead]
- ssivark 5mo agoIsn't the ovum supposed to be a single cell? Eggs of various species can be substantially larger than this.
- lmm 5mo agoYes. I remember reading that Ostrich eggs are the largest single cells (in terms of mass/volume; Blue Whale nerve cells are longer).
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- mr_toad 5mo agohttps://en.wikipedia.org/wiki/Xenophyophorea https://en.wikipedia.org/wiki/Xenophyophorea
- OrderlyTiamat 5mo agorelatedly, foraminifera are single cellular organisms that can grow up to 20 cm! https://en.wikipedia.org/wiki/Xenophyophorea https://en.wikipedia.org/wiki/Xenophyophorea
- AgentMasterRace 5mo agoExactly
- acheron 5mo agoThere’s also the one that almost ate the Enterprise. https://en.wikipedia.org/wiki/The_Immunity_Syndrome_(Star_Trek:_The_Original_Series) https://en.wikipedia.org/wiki/The_Immunity_Syndrome_(Star_Tr...
- teravor 5mo ago> The entire cell contains several cytoplasmic domains, with each domain having a nucleus and a few chloroplasts. it reinvented being multi-cellular
- api 5mo agoIt uses container based virtualization under a single host kernel instead of VM based virtualization.
- shevy-java 5mo agoAgreed. Humans draw rather arbitrary distinctions. It was quite funny in regards to viruses, aka parasite. Mimivirus are still a parasite, of course, but they even encode genes for metabolic pathways and are larger than some bacteria. See: "The Mimivirus is a giant virus that infects amoebae and was long considered to be a bacterium due to its size." https://pmc.ncbi.nlm.nih.gov/articles/PMC9133948/ https://pmc.ncbi.nlm.nih.gov/articles/PMC9133948/ Although for me, I always used the definitions through the genetic information available (genome). So as long as a virus still is a parasite, I'd hold up that definition. It will be interesting when viruses are found that are even closer to a cell, e. g. some life cycle where they could switch between parasitism and stand-alone metabolism (or some hybrid in between; I mean if they can encode whole metabolic pathways, at the least some or some parts of it, the threshold here should not be impossible to overcome, and then the whole definition of a virus also has to be adapted since it would no longer make sense).
- chasil 5mo agoPerhaps what you are seeking "retrotransposons," an endogenous retrovirus. https://en.wikipedia.org/wiki/Retrotransposon#Endogenous_retrovirus https://en.wikipedia.org/wiki/Retrotransposon#Endogenous_ret...
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- reubenswartz 5mo agoThese 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.
- shevy-java 5mo ago> largest prokaryote: 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-ever-discovered-has-unexpectedly-complex-cells 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.
- socalgal2 5mo agoCells are small? compared to what? An ostrich egg is a single cell
- graypegg 5mo agoI don't know for sure here, but isn't the ostrich IN the egg a multicellular animal? I would assume the first point where the egg contains anything that will become the ostrich, mitosis is happening to make more ostrich cells. I'm assuming there's always cell walls and nucleuses every step of the way here, and the egg and ostrich are never just one big cell. I could be off base here though, I'm really channeling grade 9 bio class from decades ago!
- limbero 5mo agoYou're correct, but only for fertilized eggs. Unfertilized eggs are single cells.
- devilbunny 5mo agoSurrounded by a bunch of stuff that isn’t the ovum. “There is at most one cell in an unfertilized bird egg” is not the same as “an unfertilized bird egg is one cell and nothing more”.
- otherme123 5mo agoThe trick is that the egg is a ball with one small cell (the ovum) that happens to have also a huge reservoir of food for the future ostrich. There is a moment when there is only once cell in the egg, just after the fussion of the ovum and the sperm cell.
- knappa 5mo agoUnfertilized bird eggs are single cells, fertilized eggs should be multicellular by the time they are laid.
- jackmalpo 5mo agoskeletal muscle cells can be many cm in length
- kayo_20211030 5mo ago> A simplistic answer is that evolution has made each cell the size best suited to its function. Yeah. That's probably it. Really, it probably is the right answer.
- fluoridation 5mo agoThat just kicks the can forward one step. What parameters control the optimal size of a given cell?
- teravor 5mo agothere is likely evolutionary pressure against large cell size (selfish genes; larger cell takes energy away from replication, provides more opportunity for infiltration by other genes, fewer gene backups in other cells, etc) while occupying a niche puts pressure to be a certain size. it lands somewhere in the middle.
- taneq 5mo agoWhy are things the way they are? Because it works better. Simple, really. :D
- limbero 5mo agoNitpick 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.
- hatthew 5mo agoSome back of the envelope math says this is true. A conservative estimate for the size of an alpha motor neuron axon is 10μm diameter and 1m long, which already puts it over an order of magnitude larger than the 4,000,000µm³ oocyte quoted in the article.
- NoMoreNicksLeft 5mo agoThis almost feels like cheating. Why not count hair follicles with hair attached then?
- mbauman 5mo agoThat's very different; hair doesn't perform membrane transport along its length. The surface of an axon is critical to the cell's functioning. https://en.wikipedia.org/wiki/Axolemma https://en.wikipedia.org/wiki/Axolemma
- hatthew 5mo agoIn addition to what mbauman said, hair follicles and the hair itself are not single-cell. I can't immediately find the composition and average cell size, but even a long and thick strand of hair is less than 2 orders of magnitude larger than the largest neurons. I doubt any individual hair cell is very large.
- gus_massa 5mo agoI agree, except the Squid Gian Axon https://en.wikipedia.org/wiki/Squid_giant_axon https://en.wikipedia.org/wiki/Squid_giant_axon that can "1mm diameter and almost 1m long" https://www.understandinganimalresearch.org.uk/using-animals-in-scientific-research/animal-research-species/squid https://www.understandinganimalresearch.org.uk/using-animals...
- gilleain 5mo agoSurface area to volume ratio?
- dmd 5mo agoThat's literally the first thing in the article.
- gilleain 5mo agoYou got me. Usually I read them. edit: Huh. Actually not a bad read. It even mentions ' On Growth and Form' which is interesting, if outdated. There are more modern texts like 'Shapes', 'Flow', and 'Branches' by Philip J Ball.
- Imnimo 5mo agoThis reminds me also of this paper: https://www.pnas.org/doi/pdf/10.1073/pnas.1115585109 https://www.pnas.org/doi/pdf/10.1073/pnas.1115585109 "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."
- RataNova 5mo agoThat framing makes the article feel even more interesting, because it's not just "cells are small because diffusion gets slow". There's also an energy budget behind it
- Terr_ 5mo agoReminds me of: "Gravity plays a role in keeping cells small" [0] [0] https://www.princeton.edu/news/2013/10/24/gravity-plays-role-keeping-cells-small https://www.princeton.edu/news/2013/10/24/gravity-plays-role...
- why_at 5mo agoI'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.
- shevy-java 5mo agoTardigrades are really cute. https://i.imgur.com/9BoxjK8.jpeg https://i.imgur.com/9BoxjK8.jpeg Some call them water bears. I am not quite sure they look like bears (six leg bear?) but the stubbly legs are indeed cute.
- Someone 5mo ago> I am not quite sure they look like bears From the front, they somewhat do. See https://uconnladybug.wordpress.com/wp-content/uploads/2013/01/waterbear-univesity-of-nort-texas1.jpg https://uconnladybug.wordpress.com/wp-content/uploads/2013/0...
- ablob 5mo agoI 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?
- firefax 5mo agomaybe god is small too?
- BurningFrog 5mo agoCells are small compared to humans because we're made up by around 3×10¹³ cells.
- IAmBroom 5mo agoAn odd way to look at it. 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?
- nxy 5mo agoPerhaps 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.
- dennyabraham 5mo agoAside 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
- RataNova 5mo agoI like explanations like this because they make biology feel much less arbitrary
- arc-in-space 5mo agoAm I getting overly paranoid, or does this account look incredibly unnatural?
- ChrisKnott 5mo agoYes too much “it’s not X it’s Y”, and too few references to personal actions/biography.
- lukan 5mo agoI also got curious, this is the most personal comment I could find https://news.ycombinator.com/item?id=44498083 https://news.ycombinator.com/item?id=44498083 Funny, but might as well be generic, trained from reddit comments. What a time we live in.
- nickpp 5mo agoSuch sleeper accounts, slowly acquiring clout and time on the platform are often used by botnets. One day they (or their actions) will be sold to the highest bidder to upvote a comment, support an idea, ideology, politician or party or some virtual product, stock or coin.
- lukan 5mo agoPossible and that is definitely a thing, but I personally I would not rule out, that there still can be a human behind it, just with that specific style and careful about his privacy.
- warrantisall 5mo ago[flagged]
- purplehat_ 5mo agoOn 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. https://teaching.hkaiser.org/fall2025/csc7103/course/papers/HaldaneRightSize.pdf https://teaching.hkaiser.org/fall2025/csc7103/course/papers/... (PDF 50 KB, 5 pages essay + 3 pages commentary)
- gkoenig 5mo agoMan that was great great great! Recommending for coworkers, I suscribed! Thanks for the good work
- myrmidon 5mo agoNice 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.
- CommenterPerson 5mo agoGreat concepts, very well written, Kudos to the writer! I bookmarked your main site. Also : as usual, lots of HN type nitpicking in the comments, most missing the main story.
- efavdb 5mo agoFWIW 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. https://arxiv.org/abs/1312.0674 https://arxiv.org/abs/1312.0674
- tsoukase 5mo agoAll 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.