# How does a tree work?

Veritasium did a great set of videos on this subject and the answer is not at all straight forward (well - not to me anyway!!)

Here's the link to the first video... the "answer" video is linked from the end of this one

You're getting beyond my realm .
I do not know what realm means but I guess it means that I'm too ignorant :)
Water has molecular weight pf 18 (two hydrogens and one oxygen.)
Air that's dry is a mix of gases that approximate a molecular weight of 29. (4/5 nitrogen, 1/5 oxygen)
A mole of air contains Avogadro's Number of molecules and the more water vapor molecules in it the lighter that mole is.
Therefore adding water vapor to air lightens it . It'd be not much of an exaggeration to say "Steam floats".
Interesting facts. One question though, how does water become vapor in the first place? I still think that (average) temperatures way lower than the boiling point can't make water turn into vapor if not for "my" idea above which by the way is quoted from Swedish Wikipedia.
Have fun watching physics at work in your everyday experiences.

Best regards, Edison
PS
It is an extremely interesting fact that there is an analogy to electron tubes here. Edison Bias is based upon the fact that some of the electrons "boiling" at the hot cathode actually has enough "peak" temperature (or peak kinetic energy) that they can reach the grid by their own (and with the aid of a 10M+ Ohm grid resistor, bias the tube).

How do the nutrients formed by photosynthesis is the leaves get transported down to the trunk and the roots? Actually, I'm thinking of molecules more than complex nutrients. The trunk and roots have lots of carbon that I think was captured from the atmosphere. I'm trying to imagine how it got down there from the leaves.
Nutrients are generally transported throughout the plant's tissue through the phloem. The phloem can be visualized as a network of tubes connecting places where nutrients are produced or taken in (source areas) and places that use or store the nutrients (sink areas).
Cells are capable of both actively and passively transporting materials across their cell membrane. Indeed, regulating the transport of materials into and out of the cell is one of the key functions of the cell membrane. Cells in source areas move nutrients into the phloem tubes. Cells in the sink areas remove the nutrients they need from the phloem tubes. If you have a tube of fluid with stuff being added on one side and taken out on the other side, the fluid in the tube will move from the place where it is being added to the place where it's being taken out.

Hi Drakkith!

This was a long article but I promise to read it all at a later time.

In the mean time I am fascinated that photosynthesis gives rise to ordinary sugar or:

$$6CO_2+6H_2O+{light}->C_6H_{12}O_6+6O_2$$

Thus Carbondioxide+Water+UV->Sugar+Oxygen

I thank you very much for this link, extremely interesting!

Best regards, Edison
PS
The light might however not be of UV type only(?)

Drakkith
Staff Emeritus
2018 Award
The light might however not be of UV type only(?)
I'm not sure, but I don't believe photosynthesis uses UV light at all. I think it uses different parts of the visible spectrum depending on the exact pigments used.

256bits
Gold Member

How do the nutrients formed by photosynthesis is the leaves get transported down to the trunk and the roots? Actually, I'm thinking of molecules more than complex nutrients. The trunk and roots have lots of carbon that I think was captured from the atmosphere. I'm trying to imagine how it got down there from the leaves.
Wiki once more.
Actually nutrients will travel either way, or sometimes both ways, both ways depending upon where the tree is in its growing season.
https://en.wikipedia.org/wiki/Phloem

anorlunda
Mentor
phloem
Thank you both. Phloem was the key word I lacked. The wiki article helped.

I'm curious if anyone has done a very physics-oriented non-biological-oriented experiment on trees -- a mass balance.

Let's say that a tree adds one metric ton of wood mass in one growing season. Applying conservation of mass, the mass of nutrients going up to the crown, must be at least one metric ton less than the mass of nutrients in the sap flowing down in the phloem. Measuring that mass balance would be an interesting and challenging experiment to perform. Has it been done to your knowledge?

Water makes it more challenging. The mass of water need not balance because water can be absorbed by roots and evaporate in the crown. Also, the mass of wood added in the season would have to be corrected for the water content of the new wood.

Thank you both. Phloem was the key word I lacked. The wiki article helped.

I'm curious if anyone has done a very physics-oriented non-biological-oriented experiment on trees -- a mass balance.

Let's say that a tree adds one metric ton of wood mass in one growing season. Applying conservation of mass, the mass of nutrients going up to the crown, must be at least one metric ton less than the mass of nutrients in the sap flowing down in the phloem. Measuring that mass balance would be an interesting and challenging experiment to perform. Has it been done to your knowledge?

Water makes it more challenging. The mass of water need not balance because water can be absorbed by roots and evaporate in the crown. Also, the mass of wood added in the season would have to be corrected for the water content of the new wood.
Plants have been grown on scales many times. The water flow you mention makes it difficult to measure the up and down differences. And a great deal if the new mass is not sent to the roots. A tree adds a new ring, branches get longer. A plant adds mass above the roots, and has water flowing continuously upward. You could easily measure root mass and mass above the surface. But I'm not sure what question you are getting at. Plants mobilize resources. That is known. It is not hard to grow plants, and weigh them, either cut up or whole.

I recall a lab that was trying to use MRI on plants to track nutrient flow, but they were more focused on WHAT things are being transported, rather than mass amounts. I worked in a lab that spent a lot of time looking at the yield of corn plants, seed weight and number of seeds per ear, and how to increase those. Yield studies are definitely an important part of plant work.

I'm not sure, but I don't believe photosynthesis uses UV light at all. I think it uses different parts of the visible spectrum depending on the exact pigments used.

"Most organisms that utilize photosynthesis to produce oxygen use visible light to do so"

So I was wrong in my assumption.

Best regards, Edison

It isn't suction or capillary action. Tree cells actively pump water.

jim hardy
Gold Member
2018 Award
Dearly Missed
It isn't suction or capillary action. Tree cells actively pump water.
It might validate my long held but utterly baseless opinion that alternate tension/compression{think deflection in a beam) as they sway in the breeze provides the motive force.

It might validate my long held but utterly baseless opinion that alternate tension/compression{think deflection in a beam) as they sway in the breeze provides the motive force.
I learned it when earning my biology degree.

jim hardy
Gold Member
2018 Award
Dearly Missed
Can you describe the mechanism ?

I'm sorry to disturb you in that interesting discussion but I just wish to say something. I have read some of Drakkith nicely provided wiki-link about phosynthesis. It describes the situation of free electrons. I don't really understand it but it got me thinking of the photo-electric effect. Is it perhaps this that is going on in the leaves? A photon splits the ionic chemical bound in Carbondioxide into Carbon and Oxygen, another photon then separates Hydrogen from the Oxygen in water and together in special doses they form Sugar and Oxygen. I think it is extremely interesting that except for the amazing Oxygen, photosynthesis produce Sugar to give the plant energy to sustain life. The rest of growth is made by extracting nutricians from the ground. What does this tell us, sometimes fat people like me that sit on our asses most of the time? Maybe we should not consume so much sugar because it is pure energy :)

Best regards, Edison

jim hardy
Gold Member
2018 Award
Dearly Missed
Maybe we should not consume so much sugar because it is pure energy :)
Off topic

Do you notice sugar affecting your mood?
Search on these terms : diabetes obesity sugar LCHF ketosis

There is a growing school of thought that US consumption rate of sugar is a danger to public health.

I just bought myself a \$20 blood sugar test kit at Walmart.

More off topic, if I may?

I am a dedicated fan of LCHF which I think is based on the way cavemen ate (and who has "seen" a fat caveman?). I also think that what you call ketosis goes something like this: If you cancel the corbonhydroxides (CH) in your food, the cells switch from burning CH to burning fat. My thought about this is the that while they are saying that there are two kinds of CH (i.e fast/slow) both contains exactly the same amount of energy and CH is CH regardless if there are parts of it that is called sugar (of different names). The only difference is the rate of sugar "shock" to the sugar regulating system (i.e insulin production). And look at a person about to run Marathon, what does he/she eat? Yes, they eat pasta i.e slow CH. And run for 50km...

All this while I hardly even run for the bus :D

Best regards, Edison
PS
I really do not experience moodswings due to sugar. If I experience anything it's more like nausea due to too much sugar. I have never experienced less of tiredness. Coffee works better :)

Evo
Mentor