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Most root hairs are unicellular but why is it so? What advantages does a plant derive from a unicellular root hair that it couldn't have if it was multicellular?

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    $\begingroup$ I have edited your question because 'Root hair cells are unicellular' is wrong it should be root hairs only. $\endgroup$ – Tyto alba Jan 18 '17 at 17:36
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    $\begingroup$ @Abcd Seemingly User SanjuktaGhosh meant "A Cell" means unicellular because Uni=1. You can't get a "multicellular cell". That is impossible due to Grammar. For example we could found "Multicellular stem-hairs" but not "stem-hair cells are multicellular" $\endgroup$ – Always Confused Jan 18 '17 at 18:21
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    $\begingroup$ @Abcd A cell cannot be unicellular. That's all. $\endgroup$ – Tyto alba Jan 18 '17 at 18:50
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    $\begingroup$ @Abcd "Hairs" is a valid word in English. However, "hair" can refer to either a singular hair or to a whole section, so that the correct usage when you are talking about "hair color" or getting a "hair cut" or referring to "pubic hair" is to not use "hairs": it's more of a synonym for "fur" in these contexts. However, "hairs" still is correct and used in certain contexts such as a descriptive context: "oh look at all those little hairs on that caterpillar!" or if you are referencing numbers "his head was bald except for 4 hairs" and a few other contexts. $\endgroup$ – Bryan Krause Jan 18 '17 at 20:09
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    $\begingroup$ I though that unicellular is attribute for organisms, not organs $\endgroup$ – altroware Jan 18 '17 at 20:42
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A couple reasons come to mind.* The purpose of root hairs is absorbtion. If you consider multiple cells along the length of the hair, additional cell walls and plasma membranes would somewhat impede the movement of nutrients.

More importantly, the absorbtion is a function of the surface area of the hair. Smaller diameter (one cell thick) hairs provide greater surface area to volume ratio. While it's true that a larger diameter, due to multiple cells, might offer greater overall surface area, it would come at the expense of requiring more volume compared to a greater number of smaller hairs.

For example, suppose you have a certain volume of cutoplasm to spend on making root hairs. For the sake of the example, suppose the hairs are of a fixed length. If you make the hairs half the diameter you will be able to provide twice the overall surface area using the same volume of material.

* By this I mean I don't know the ultimate (evolutionary) reason and I doubt anyone does. This is probabably not an active area of research and you're not likely to find definitive answers with research. So, my answer, if you will, is conjecture.

That said, it is educated conjecture. In 24 years of teaching AP Biology, the relationship of volume versus surface area has arisen multiple times. One of the exercises I gave my students, in preparation for the exam, was to find at least ten examples. Some of the best students found many more.

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  • $\begingroup$ Can you please add some citations to your answer? $\endgroup$ – Bryan Krause Jan 18 '17 at 18:06
  • $\begingroup$ @BryanKrause I think this answer is primarily based upon logic. Still, if there pre-exists any published documents; that would be purely hypothetical. It doesn't seems plants would die if someone developed by GM some > 1 cellular root-hairs. It happens maybe just because this trait evolved accidentally $\endgroup$ – Always Confused Jan 18 '17 at 18:17
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    $\begingroup$ @AlwaysConfused I don't disagree with the logic posted, there should still be citation just because that's how this site works. I've gotten a lot of criticism myself when I've posted uncited answers :) $\endgroup$ – Bryan Krause Jan 18 '17 at 18:33
  • $\begingroup$ @BryanKrause This is simple math, as diameters increase, volumes get larger faster than surface area. As far as afirming these reasons are an ultimate cause, I doubt that can be done; that's why I phrased it in the manner I did. Maybe you'd like to put this question in the catagory of requiring an "opinion based" answer. But, as an educatior, I think it's a good one for offering opportunities to model generalized scientific reasoning. Surface area versus volume ratio is a recuring theme in Biology, explaining a myriad of observations. $\endgroup$ – bpedit Jan 18 '17 at 20:10
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    $\begingroup$ I'm not arguing with the math or the logic. I am saying you should find an authoritative source that agrees with what you wrote. Sometimes, especially in biology, the most obvious math or logic turns out to be wrong because of some other misunderstood concept. I don't think that's going on here, but just to have a reference to a biology/botany textbook that says this fact, rather than person on the internet @bpedit says this fact is just part of the good standards on this site. $\endgroup$ – Bryan Krause Jan 18 '17 at 20:13

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