Water goes up in plants by cappilary action. So that should also explain water inside coconuts.

My doubt relates to the easy experiment of transfering water from a filled glass to an empty one using some chord or even a toilet paper pressed as a chord.

Even if the paper is initially dry, water is gradually transferred until levels are equal at both glasses.

But it is not possible (at least I couldn't make happen) to transfer any drop of water to an empty glass whose bottom is above the water level of the filled glass.

So how is it possible for a coconut? Maybe its internal pressure is below atmospheric?

I know there are other similar questions, but the answers tends to follow the capillarity action (what is obvious to me, but seems incomplete), or postulates great negative pressures. (But if it is 1 atm outside, at most it should be zero inside, and a perfect vaccum inside plants is too strange).

But there is maybe some combined effect of capillarity and negative pressure that is not well discussed so far.

  • $\begingroup$ The answer of biology stack exchange mentions negative pressure, which is also my idea. It should be possible through a small hole and a pressure meter to know the pressure inside a coconut. $\endgroup$ – Claudio Saspinski Feb 2 at 1:04
  • $\begingroup$ Here is a Veritasium video on how trees get water to the top. Nothing about coconuts in particular. youtube.com/watch?v=BickMFHAZR0 $\endgroup$ – mmesser314 Feb 2 at 1:13
  • $\begingroup$ @mmesser314 this video, as many others, starts discussing normal suction, what is obviously not the solution due to the 10m limit. But in the end returns with strange numbers like -15 atm. I suppose that a small negative pressure + capillarity action could pour some drops of water in a empty glass from a fill glass below it. But it is hard to make such an experiment. $\endgroup$ – Claudio Saspinski Feb 2 at 1:38
  • $\begingroup$ Trees are living things so it is dangerous to try to explain everything happening in trees with static physics. There are little pumps in cell surfaces. There are little vehicles and rails inside cells. Cells can transport compounds in and out against physics pressures, including capillary or osmosis or whatever pressures, as long as energy is supplied. I have physics background and I once tried to explain everything with physics. Now I work in a position related to biology. I know how naive I was. $\endgroup$ – verdelite Feb 2 at 5:32
  • $\begingroup$ @verdelite However, conduction of water is plants is a purely passive process and no energy is used. Energy(in the form of ATP) is used for the transport of food material in the phloem. $\endgroup$ – Sam Feb 2 at 15:25

Water goes up in plants by capillary action

This is a common misconception. Capillary action is believed to play a small role but fails to explain how water is carried to heights greater than 1 meter. Water in transported through the xylem vessels (water-carrying tubes) mainly through two processes-

1) Osmosis occurs due to the difference in osmotic pressure between the region inside the root cells and in the soil. Hence water flows into the roots to equalize the pressure difference which is actively maintained by the plant.

2) Transpiration from the stomata at the leaves leads to negative pressure being developed at the top of the water column. This is known as transpiration pull and it causes the water to rises upwards in the vessels.

This is the currently accepted model of xylem conduction in plants. Do not confuse osmotic pressure and air pressure as they are completely different. Most conduction in plants makes use of osmotic pressure caused by a combination of water potential $(\psi_w)$ and solute potential $(\psi_s)$.

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  • $\begingroup$ this link herbarium.millersville.edu/class-web/botany2010/lab11-water.pdf $\endgroup$ – anna v Feb 2 at 5:28
  • $\begingroup$ Negative pressure? Do you mean negative relative to some other pressure? Which? $\endgroup$ – sammy gerbil Feb 3 at 4:22
  • $\begingroup$ @sammygerbil The region at the top of the vessel has lower water potential as compared to the bottom of the vessel. $\endgroup$ – Sam Feb 3 at 4:28

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