[HN Gopher] Why are cells small?
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Why are cells small?
Author : mailyk
Score : 128 points
Date : 2026-06-08 19:10 UTC (10 hours ago)
(HTM) web link (burrito.bio)
(TXT) w3m dump (burrito.bio)
| chasil wrote:
| Not all are?
|
| Largest eukaryote:
|
| https://en.wikipedia.org/wiki/Valonia_ventricosa
|
| largest prokaryote:
|
| https://en.wikipedia.org/wiki/Thiomargarita_namibiensis
| DaveSchmindel wrote:
| > 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 wrote:
| Interesting topology. How empty is the vacuole?
| trumpdong wrote:
| empty in terms of normal cell components, apparently it
| stores relatively huge amounts of nitrates that are a
| necessary energy source for it
| vasco wrote:
| > This is in line with biology's only rule: namely, there are
| exceptions to every rule!
|
| Nice paradox
| embedding-shape wrote:
| 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.
| malfist wrote:
| When they invade your saltwater aquarium, you won't think
| they're small. They can get up just slightly larger than a
| marble
| ssivark wrote:
| Isn't the ovum supposed to be a single cell? Eggs of various
| species can be substantially larger than this.
| lmm wrote:
| Yes. I remember reading that Ostrich eggs are the largest
| single cells (in terms of mass/volume; Blue Whale nerve cells
| are longer).
| mr_toad wrote:
| https://en.wikipedia.org/wiki/Xenophyophorea
| OrderlyTiamat wrote:
| relatedly, foraminifera are single cellular organisms that can
| grow up to 20 cm! https://en.wikipedia.org/wiki/Xenophyophorea
| AgentMasterRace wrote:
| Exactly
| acheron wrote:
| There's also the one that almost ate the _Enterprise_.
| https://en.wikipedia.org/wiki/The_Immunity_Syndrome_(Star_Tr...
| teravor wrote:
| > The entire cell contains several cytoplasmic domains, with
| each domain having a nucleus and a few chloroplasts.
|
| it reinvented being multi-cellular
| api wrote:
| It uses container based virtualization under a single host
| kernel instead of VM based virtualization.
| shevy-java wrote:
| Agreed. 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/
|
| 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).
| reubenswartz wrote:
| 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.
| shevy-java wrote:
| > 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-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.
| WorkerBee28474 wrote:
| Another answer is: They're not - at least in some plants:
|
| https://en.wikipedia.org/wiki/Valonia_ventricosa
|
| https://en.wikipedia.org/wiki/Acetabularia
| socalgal2 wrote:
| Cells are small? compared to what? An ostrich egg is a single
| cell
| graypegg wrote:
| I 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 wrote:
| You're correct, but only for fertilized eggs. Unfertilized
| eggs are single cells.
| devilbunny wrote:
| Surrounded 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 wrote:
| The 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 wrote:
| Unfertilized bird eggs are single cells, fertilized eggs
| should be multicellular by the time they are laid.
| jackmalpo wrote:
| skeletal muscle cells can be many cm in length
| otherme123 wrote:
| A neuron can be more than 1 meter long in humans, more than
| 20 meter in a whale.
| bilsbie wrote:
| 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.
| saulpw wrote:
| The yolk is an energy/vitamin source, not a 'cell'. The
| division happens outside the yolk.
|
| From Wikipedia:
|
| > The yolk is not living cell material like protoplasm, but
| largely passive material
| al_borland wrote:
| I had to go look this up, as I had heard the egg thing my
| whole life and just accepted it.
|
| It turns out the oocyte is the single cell inside the egg,
| which for birds is significantly larger than a typical cell.
| So in that respect, the cell in a bird egg is very large.
| However, compared to the egg itself, it's tiny. The yolk and
| whites in the egg are all to provide nutrients as it grows,
| if fertilized.
| ErroneousBosh wrote:
| One of the fascinating things about biology I think is this -
| that if the cells of your body were the size of an egg,
| they'd be way, way too big and you'd probably die.
| trumpdong wrote:
| I also find it interesting that if your spleen were to go
| prompt critical, it would irradiate you and you'd probably
| die. That is my favorite fact about nuclear physics.
| kayo_20211030 wrote:
| > 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 wrote:
| That just kicks the can forward one step. What parameters
| control the optimal size of a given cell?
| teravor wrote:
| there 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 wrote:
| Why are things the way they are? Because it works better.
| Simple, really. :D
| limbero wrote:
| 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.
| hatthew wrote:
| Some back of the envelope math says this is true. A
| conservative estimate for the size of an alpha motor neuron
| axon is 10mm diameter and 1m long, which already puts it over
| an order of magnitude larger than the 4,000,000um3 oocyte
| quoted in the article.
| NoMoreNicksLeft wrote:
| This almost feels like cheating. Why not count hair follicles
| with hair attached then?
| mbauman wrote:
| That'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
| hatthew wrote:
| In 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 wrote:
| I agree, except the Squid Gian Axon
| https://en.wikipedia.org/wiki/Squid_giant_axon that can
| "1mm diameter and almost 1m long"
| https://www.understandinganimalresearch.org.uk/using-
| animals...
| CrazyStat wrote:
| Giraffes neurons can be up to 15 feet long. Blue whales are
| speculated to have neurons up to 100 feet long, though they've
| never been directly observed (dissected).
| Kaliboy wrote:
| But neurons are electrical no? I suppose maybe that's why
| they're not in the comparison.
|
| Or does that work with diffusion too?
| gilleain wrote:
| Surface area to volume ratio?
| dmd wrote:
| That's literally the first thing in the article.
| gilleain wrote:
| You 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 wrote:
| This reminds me also of this paper:
| 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 wrote:
| That 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_ wrote:
| Reminds me of: "Gravity plays a role in keeping cells small" [0]
|
| [0] https://www.princeton.edu/news/2013/10/24/gravity-plays-
| role...
| why_at wrote:
| 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.
| shevy-java wrote:
| Tardigrades are really cute.
|
| 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.
| ablob wrote:
| 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?
| NuclearPM wrote:
| What does amount of molecule mean?
| RataNova wrote:
| Maybe the better takeaway is not "larger cells can't work" but
| "larger cells need to pay for increasingly elaborate
| workarounds"
| firefax wrote:
| maybe god is small too?
| BurningFrog wrote:
| Cells are small compared to humans because we're made up by
| around 3x1013 cells.
| nxy wrote:
| 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.
| dennyabraham wrote:
| 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
| RataNova wrote:
| I like explanations like this because they make biology feel much
| less arbitrary
| warrantisall wrote:
| Cells are bad.
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