# Cell size? **URL:** \ **Category:** Factual Questions\ **Created:** [August 14, 2022, 4:32pm UTC](https://boards.straightdope.com/t/cell-size/969645 "2022-08-14T16:32:16Z")\ **Posts on this page:** 17\ **Page:** 3
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 16, 2022, 2:34am UTC](https://boards.straightdope.com/t/cell-size/969645/41 "2022-08-16T02:34:13Z")
I see a mod note has been posted. I hope my post is not considered arguing with mod guidance. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 16, 2022, 10:52pm UTC](https://boards.straightdope.com/t/cell-size/969645/42 "2022-08-16T22:52:59Z")
> [@DSeid](#): > > And I stand by the point. Comments like “your understanding—isn’t.” when the understanding as expressed is pretty much on target for a generally well educated person, should be corrected. You mean where the poster repeatedly spoke about mitochondria in the nucleus, which is precisely where mitochondria are not? ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 17, 2022, 12:34am UTC](https://boards.straightdope.com/t/cell-size/969645/43 "2022-08-17T00:34:42Z")
In fact yes I do. I spend much of my days explaining medical stuff to a wide variety of parents, many college educated in fields other than biology. Their getting the location of the mitochondria confused when they were expressing reasonable understanding about how mitochondrial genes are (generally) considered to be transmitted matrilineally only and what that implies would not lead me to declare them as “not understanding”. If you want to discuss this further please message me though. It is not the point of the thread. As to that poster’s not being able to grok why we do not consider mitochondria to be separate organisms - the simplest answer is we just don’t. But I do not myself have a good understanding of why composite organisms in obligate symbiosis, like lichen, are considered as consisting of two organisms living together, requiring each other for survival, while the idea of thinking of mitochondria as an organism that has exploited other cells to spread its genes about, seems so wrong. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 1:26am UTC](https://boards.straightdope.com/t/cell-size/969645/44 "2022-08-17T01:26:59Z")
> [@DSeid](#): > > But I do not myself have a good understanding of why composite organisms in obligate symbiosis, like lichen, are considered as consisting of two organisms living together, requiring each other for survival “All the algae and cyanobacteria are believed to be able to survive separately, as well as within the lichen; that is, at present no algae or cyanobacteria are known which can only survive naturally as part of a lichen.” From > **[Symbiosis in lichens](https://en.wikipedia.org/wiki/Symbiosis_in_lichens)** > > Symbiosis in lichens is the mutually beneficial symbiotic relationship of green algae and/or blue-green algae (cyanobacteria) living among filaments of a fungus, forming lichen. > Living as a symbiont in a lichen appears to be a successful way for a fungus to derive essential nutrients, as about 20% of all fungal species have adopted this mode of life. The autotrophic symbionts occurring in lichens are a wide variety of simple, photosynthetic organisms commonly and traditionally known as “algae”... ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [August 17, 2022, 1:37am UTC](https://boards.straightdope.com/t/cell-size/969645/45 "2022-08-17T01:37:42Z")
> [@DSeid](#): > > As to that poster’s not being able to grok why we do not consider mitochondria to be separate organisms - the simplest answer is we just don’t. But I do not myself have a good understanding of why composite organisms in obligate symbiosis, like lichen, are considered as consisting of two organisms living together, requiring each other for survival, while the idea of thinking of mitochondria as an organism that has exploited other cells to spread its genes about, seems so wrong. Thanks for the great explanations above. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 1:46am UTC](https://boards.straightdope.com/t/cell-size/969645/46 "2022-08-17T01:46:34Z")
Another good wiki article on lichens: > **[Lichen anatomy and physiology](https://en.wikipedia.org/wiki/Lichen_anatomy_and_physiology)** > > Lichen anatomy and physiology is very different from the anatomy and physiology of the fungus and/or algae and/or cyanobacteria that make up the lichen when growing apart from the lichen, either naturally, or in culture. The fungal partner is called the mycobiont. The photosynthetic partner, algae or cyanobacteria, is called the photobiont. The body of a lichens that does not contain reproductive parts of the fungus is called the thallus. The thallus is different from those of either the fungus o... > A particular fungus species and algal species are not necessarily always associated together in a lichen. One fungus, for example, can form lichens with a variety of different algae. The thalli produced by a given fungal symbiont with its differing partners will be similar, and the secondary metabolites identical, indicating that the fungus has the dominant role in determining the morphology of the lichen. Further, the same algal species can occur in association with different fungal partners. Lichens are known in which there is one fungus associated with two or even three algal species. Rarely, the reverse can occur, and two or more fungal species can interact to form the same lichen. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 17, 2022, 1:47am UTC](https://boards.straightdope.com/t/cell-size/969645/47 "2022-08-17T01:47:29Z")
My ignorance reduced! Are there examples of true _obligate_ symbiotes the partners of which are considered organisms in their own right? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 2:09am UTC](https://boards.straightdope.com/t/cell-size/969645/48 "2022-08-17T02:09:48Z")
> [@DSeid](#): > > Are there examples of true _obligate_ symbiotes the partners of which are considered organisms in their own right? I would think almost all of them? Mitochondria and [plastids](https://en.wikipedia.org/wiki/Plastid) are special extreme cases where the bacterial genome has been reduced so much that I don’t think that is meaningful to even _call_ it a symbiotic relationship anymore. A mitochondrion or plastid wouldn’t survive outside a cell, but neither would a lysosome or a golgi apparatus, both of which may possibly—along with other organelles—have once been independent organisms that became symbionts but have lost _all_ their genes. (That is a real theory, though not one with the smoking guns of mitochondria and plastids.) ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 2:14am UTC](https://boards.straightdope.com/t/cell-size/969645/49 "2022-08-17T02:14:45Z")
BTW, the reason mitochondria retain any genes at all may be because it is functionally necessary: > **[Why do our cell's power plants have their own DNA?](https://www.science.org/content/article/why-do-our-cells-power-plants-have-their-own-dna)** > > Study suggests that mitochondrial DNA may provide local control ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 17, 2022, 2:26am UTC](https://boards.straightdope.com/t/cell-size/969645/50 "2022-08-17T02:26:57Z")
> [@Darren\_Garrison](#): > > A mitochondrion or plastid wouldn’t survive outside a cell, And the cell would not survive without it. But the point is that they are not so different or extreme compared to other true obligate symbionts in that regard. They are a very fundamental example of that relationship, yes. But if I understand correctly the Protozoa adapted for termites would not survive elsewhere and the termites would die without them. So on. Being in an obligate symbiotic relationship seems insufficient to be the justification of its exclusion as “organism”. It may simply be the ancientness and pervasiveness of the relationship. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 2:40am UTC](https://boards.straightdope.com/t/cell-size/969645/51 "2022-08-17T02:40:10Z")
> [@DSeid](#): > > But the point is that they are not so different or extreme compared to other true obligate symbionts in that regard. And I disagree with this assessment. I think that the gene reduction is mitochondria is indeed _very_ extreme and beyond the point that it can be reasonably called a seperate organism. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 17, 2022, 2:57am UTC](https://boards.straightdope.com/t/cell-size/969645/52 "2022-08-17T02:57:46Z")
So to make sure I understand your position - it’s not that it could not survive without its partner, but the fact that it’s DNA has been pared down that disqualifies it as “organism”? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 3:13am UTC](https://boards.straightdope.com/t/cell-size/969645/53 "2022-08-17T03:13:06Z")
Yes. Not only are almost all the genes gone, but the few that are left are for very specific purposes in service of the greater cell. It is the vestigial stump of a former organism. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 17, 2022, 3:44am UTC](https://boards.straightdope.com/t/cell-size/969645/54 "2022-08-17T03:44:52Z")
On consideration not only does that convince me, but I’ll add to the position - the way it accomplished that paring was not actually being done by eliminating those genes. In many cases it off loaded them to the cell’s nuclear in a unilateral transfer. > **[Evolution of mitochondrial gene content: gene loss and transfer to the nucleus...](https://pubmed.ncbi.nlm.nih.gov/14615181/)** > > Mitochondrial gene content is highly variable across extant eukaryotes. The number of mitochondrial protein genes varies from 3 to 67, while tRNA gene content varies from 0 to 27. Moreover, these numbers exclude the many diverse lineages of... So it isn’t only “renting space” for its very pared down genes, it has merged most of its ancient genetic self into the host’s genes permanently. That’s far beyond obligate symbiosis. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 17, 2022, 6:29am UTC](https://boards.straightdope.com/t/cell-size/969645/55 "2022-08-17T06:29:07Z")
> [@DSeid](#): > > So it isn’t only “renting space” for its very pared down genes, it has merged most of its ancient genetic self into the host’s genes permanently. That’s far beyond obligate symbiosis. Right—it is similar to the many viruses that have integrated into eukaryote DNA, which includes some viral genes that still perform functions. [https://newsroom.uw.edu/news/genes-‘fossil’-virus-human-dna-found-be-active](https://newsroom.uw.edu/news/genes-%E2%80%98fossil%E2%80%99-virus-human-dna-found-be-active) ---
**Author:** ![psychonaut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/psychonaut/32/4655_2.png) [@psychonaut](https://boards.straightdope.com/u/psychonaut)\ **Post date:** [August 17, 2022, 10:53am UTC](https://boards.straightdope.com/t/cell-size/969645/56 "2022-08-17T10:53:30Z")
> [@gnoitall](#): > > The human ovum is about 1mm, large enought to see with the naked eye. I hear the ostrich ovum is also pretty macroscopic. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 18, 2022, 12:15pm UTC](https://boards.straightdope.com/t/cell-size/969645/57 "2022-08-18T12:15:31Z")
Returning to the op there is this one to consider, the largest organism on our planet. > **[Strange but True: The Largest Organism on Earth Is a Fungus](https://www.scientificamerican.com/article/strange-but-true-largest-organism-is-fungus/)** > > The blue whale is big, but nowhere near as huge as a sprawling fungus in eastern Oregon I don’t however know how large the individual cells of this fungus are. I do have some vague memory that fungal cells often fuse and are often considered as having very large cells with multiple nuclei … I am not recalling the details however. Anyone able to fill that part in for me? [Previous page](https://boards.straightdope.com/t/cell-size/969645.md?page=2)