Why are cells small? • Hacker News Board

Re: Why are cells small?

#21

Post by Imnimo » Mon, Jun 08, 2026, 8:26 PM UTC

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."

Re: Why are cells small?

#22

Post by al_borland » Mon, Jun 08, 2026, 8:29 PM UTC

bilsbie wrote: post #16

socalgal2 wrote: post #4

Cells are small? compared to what? An ostrich egg is a single cell

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.

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.

Re: Why are cells small?

#23

Post by gilleain » Mon, Jun 08, 2026, 8:31 PM UTC

dmd wrote: post #12

gilleain wrote: post #11

Surface area to volume ratio?

That's literally the first thing in the article.

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 It even mentions ' On Growth and Form' which is interesting, if outdated.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.

Re: Why are cells small?

#24

Post by NoMoreNicksLeft » Mon, Jun 08, 2026, 8:31 PM UTC

hatthew wrote: post #18

limbero wrote: post #7

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.

Some 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.

This almost feels like cheating. Why not count hair follicles with hair attached then?

Re: Why are cells small?

#25

Post by malfist » Mon, Jun 08, 2026, 8:34 PM UTC

embedding-shape wrote: post #14

chasil wrote: post #2

Not all are? Largest eukaryote: https://en.wikipedia.org/wiki/Valonia_ventricosa largest prokaryote: https://en.wikipedia.org/wiki/Thiomargarita_namibiensis

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.

When they invade your saltwater aquarium, you won't think they're small. They can get up just slightly larger than a marble

Re: Why are cells small?

#26

Post by ssivark » Mon, Jun 08, 2026, 8:34 PM UTC

chasil wrote: post #2

Not all are? Largest eukaryote: https://en.wikipedia.org/wiki/Valonia_ventricosa largest prokaryote: https://en.wikipedia.org/wiki/Thiomargarita_namibiensis

Isn't the ovum supposed to be a single cell? Eggs of various species can be substantially larger than this.

Re: Why are cells small?

#27

Post by mr_toad » Mon, Jun 08, 2026, 8:43 PM UTC

chasil wrote: post #2

Not all are? Largest eukaryote: https://en.wikipedia.org/wiki/Valonia_ventricosa largest prokaryote: https://en.wikipedia.org/wiki/Thiomargarita_namibiensis

https://en.wikipedia.org/wiki/Xenophyophorea

Re: Why are cells small?

#28

Post by OrderlyTiamat » Mon, Jun 08, 2026, 8:51 PM UTC

chasil wrote: post #2

Not all are? Largest eukaryote: https://en.wikipedia.org/wiki/Valonia_ventricosa largest prokaryote: https://en.wikipedia.org/wiki/Thiomargarita_namibiensis

relatedly, foraminifera are single cellular organisms that can grow up to 20 cm! https://en.wikipedia.org/wiki/Xenophyophorea

Re: Why are cells small?

#29

Post by mbauman » Mon, Jun 08, 2026, 8:53 PM UTC

NoMoreNicksLeft wrote: post #24

hatthew wrote: post #18

Earlier quoted context omitted.

Some 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.

This almost feels like cheating. Why not count hair follicles with hair attached then?

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

Re: Why are cells small?

#30

Post by ErroneousBosh » Mon, Jun 08, 2026, 8:59 PM UTC

bilsbie wrote: post #16

socalgal2 wrote: post #4

Cells are small? compared to what? An ostrich egg is a single cell

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.

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.