14
$\begingroup$

Within a single species, how does the relative number of cells in the body relate to the relative size of the organism?

Let's say we take two humans, one of them is 6 feet tall and the other one is 5 feet tall. They have similar BMI, age, physical condition, genetic background (aside from height) and are the same sex.

Does the tall one have more cells? Or does he have bigger cells?

PS: Ideally, answers should be backed up by appropriate sources.

PPS: While I'm grateful to everyone for the very nice answers I got, I should point out that I'm waiting for an answer which includes references to accept it.

Improve this question
$\endgroup$
1
  • 2
    $\begingroup$ In retrospect, I have presented a false dichotomy. As jarlemag has pointed out, a tall person may have neither more cells nor bigger cells - their height (or size, see discussion in buzrw's answer) may be due to more non-cellular mass (eg. more ECM). $\endgroup$
    – Superbest
    Commented Apr 18, 2014 at 20:37

3 Answers 3

Reset to default
10
$\begingroup$

This is really the most fundamental concept of Cell Biology, so good question. If you look at the size of a any cell from a whale and compare it to the size of any of cells from a mouse, they are in fact quite similar, despite the extreme difference in the overall size of the organisms they are from. There is a reason why cells are small, and it has to do with the fact that they survive based on their ability to absorb enough nutrients from their environment. As a cell gets larger it needs more to survive (because it has a bigger mass). A bigger cell has also has a larger surface area around it (so it can absorb more nutrients).

HOWEVER, there gets to be a point where the mass of the cell is too large for the surface area to compensate for. Mathematically this is shown by what is called the "surface-area-to-volume ratio". Basically, it states that as a a sphere gets larger, the volume increases at a higher RATE than the surface area. So there is a reason cells get only so big, the 60's horror movie The Blob was not scientifically accurate, a single-cell that large (the blob) would not have enough surface area to absorb enough nutrients to sustain itself. Taller (or bigger) people have more cells (not bigger ones) than others.

Effects of osmotic pressure can alter cell size slightly.

When you are talking about taller individuals, you are (I think) really meaning larger people, people with a higher mass. And yes, they have more cells.

Another topic of Cell Biology you may want to explore is apoptosis. Let's say you have two individuals both 180 lbs. one of them is 5' tall and the other 7'. Both these individuals have the same number of cells, but the taller one has a higher percentage of them in the superior and inferior regions of the body. It is the process of apoptosis that sculps an organisms shape.

Improve this answer
$\endgroup$
4
  • 1
    $\begingroup$ You are correct that I, in effect, meant "larger people", because I specified that their BMI is similar. $\endgroup$
    – Superbest
    Commented Apr 8, 2014 at 19:05
  • 3
    $\begingroup$ +1 sounds like a good answer for the cell biologist that I am NOT. You may add some elements about how (and why) cell size varies from one species to another. This article also might be of interest. $\endgroup$
    – Remi.b
    Commented Apr 9, 2014 at 17:26
  • 1
    $\begingroup$ @Remi.b I'm not sure if that paper applies to my question per se, but it was a fascinating read! Thank you. $\endgroup$
    – Superbest
    Commented Apr 18, 2014 at 20:33
  • 1
    $\begingroup$ Well written, but I have 2 issues. 1. I can't imagine that 2 individuals of the same mass always have the same number of cells! Intracellular "stuff" (e.g. proteins & other macromolecules) varies b/w cell types -- think about adipose with a "full" vacuole vs RBCs. 2. Your post does not address extracellular "stuff" -- either space or non-cellular material (e.g. H2O) -- which could account for greater body size (both space and mass) . I know it's an old post, but please add some citations; otherwise I have to downvote as a "sounds good but probably isn't true" post. Thanks $\endgroup$
    – theforestecologist ♦
    Commented Dec 1, 2018 at 19:23
2
$\begingroup$

Not sure it is proven, but this paper makes use of the assumption: West et al, PNAS 99:2473, http://www.pnas.org/content/99/suppl_1/2473.full

Btw, this paper may be relevant for you as it focuses on the metabolic activity, which is not quite propotional to body mass (power 3/4: it's growing slower)

Improve this answer
$\endgroup$
1
0
$\begingroup$

The taller person has more cells. Most cells can only lengthen up to a certain point. Whilst the neuronal cells will be longer and likely some others, the rest of the cells will just be of larger number.

Improve this answer
$\endgroup$
2
  • 9
    $\begingroup$ Just to play the devil's advocate, are there actually any sources that confirm this? Couldn't it also be that tall people have the same number of cells, but with more extracellular matrix and larger spacing between the cells? $\endgroup$
    – jarlemag
    Commented Apr 8, 2014 at 9:20
  • $\begingroup$ @jarlemag That's a very good point (which I originally missed); I added a comment to my question to clarify. $\endgroup$
    – Superbest
    Commented Apr 18, 2014 at 20:37

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .