
Where does a tree get its mass? - sajid
http://thelastpsychiatrist.com/2008/11/where_does_a_tree_get_its_mass.html
======
electromagnetic
The article started by pointing out a logical incongruency that most people
have. I know better than to think the tree is made of the ground, however I
know many people are not.

However he's talking mass and reneges on his statement that trees are made
from the air by stating that many trees are over 50% water. Well IMO when
talking about mass the majority-share counts as the subjects mass origins.

The plant breaks down CO2 into C + O2 via photosynthesis. The C makes up the
plant. This is the simplified version he starts with, which was an ample
metaphor. However then he states that the tree can be predominantly water.
Meaning the plant is made up of say 60% water and 40% carbon.

However the plant is made up of predominantly of water trapped within
cellulose membranes. If we talk dry weight, we're still talking 6 carbon atoms
(72), 10 hydrogen atoms (10) and 5 oxygen atoms (80). This means roughly 66%
of the trees mass comes directly from water from the ground sequestered in its
cellulose.

This means roughly only 20% of the tree actually comes directly from carbon
sequestered from the air.

So really, where does the plant get its mass? The ground.

If you're asking where the plant gets its dry weight, still the ground by ~6%.

By tackling a logical fallacy with scientific thinking he opened the window to
be completely corrected by it himself. Trees grow because they take the carbon
out of the air. However you talk about mass and we're talking about molecular
weights.

Now if he'd have been as smart of Feynman he would have dismissed the water
quite logically again. The rain falls from the sky. Save for a few very large
trees that actually reach into the water table, trees well inland rely solely
on the rain for their supply of water. That means the 50% of its mass that is
water still technically comes from the air from moisture being condensed in
cold air and forming water droplets.

~~~
pbhjpbhj
>The rain falls from the sky. Save for a few very large trees that actually
reach into the water table, trees well inland rely solely on the rain for
their supply of water.

But they draw up that rain from the local soil using transpiration as I was
explaining to my 4yo yesterday, I'm pretty sure he'll have forgotten it by
now, I digress.

What I'm not sure about is rainwater capture - do shrubs capture (internally)
water higher up the plant (eg in at limb connections) or are leaves simply
directing the water to fall close to the "trunk" to maximise root take-up.

It's a good catch though as I'm sure I'd fall to the leap from knowing that
"trees grow by taking in CO2 and that is where they get their mass of carbon
from" to the false assumption that "tree mass comes primarily from the air"
without really thinking about it.

Thanks for your analysis.

------
chaosmachine
Feynman knows:

<http://www.youtube.com/watch?v=N1pIYI5JQLE>

~~~
ckuehne
Can't upvote you enough for this. By the way, Feynman also knows the
difference "between knowing the name of something and knowing something":
<http://www.youtube.com/watch?v=05WS0WN7zMQ>

~~~
jules
This. He really articulates clearly the difference between two ways of
thinking. Thinking by really understanding then translating the thoughts into
words and thinking by manipulating words.

------
waivej
This reminds me of a snippet from Buckminster Fuller's "Critical Path". He's
talking about specialists and generalists and how we rarely see the big
picture of what's important.

"Nobody is born a specialist. Every child is born with comprehensive
interests, asking the most comprehensively logical and relevant questions.
Pointing to the logs burning in the fireplace, one child asked me, "What is
fire?" I answered, "Fire is the Sun unwinding from the tree's log. The Earth
revolves and the trees revolve as the radiation from the Sun's flame reaches
the revolving planet Earth. By photosynthesis the green buds and leaves of the
tree convert that Sun radiation into hydrocarbon molecules, which form into
the bio-cells of the green, outer, cambium layer of the tree."

[http://www.maebrussell.com/Critical%20Path/Critical%20Path%2...](http://www.maebrussell.com/Critical%20Path/Critical%20Path%20excerpts%201.html)

------
wrs
The concept of uncertainty is hard to grasp. In my high school (1979) we were
required to use slide rules for the first year of science class, despite the
availability of inexpensive calculators. The reason was to impress upon us the
importance of significant figures, and also to develop our intuition for
orders of magnitude. Unless your slide rule is really expensive, you just
can't get more than 3 significant figures from it, which is a good match to
the accuracy of just about every measurement in high school. It also tells you
the figures without the magnitude--you have to determine in your head whether
you just calculated microns or kilometers.

------
todayiamme
An interesting thing here is that this article assumes that the way science is
taught is wrong. I do not intend to make any conclusions about this, but I
just graduated from high school and I just realized _why_ people don't learn
science as opposed to a bunch of meaningless phrases.

Although a lot of it is a broken system, but the truth is that they aren't
expected to. What is expected of them is to get good grades, and since that is
possible through rote almost all of my peers take that route. If you ask them
in a moment of honesty they say; "why should I do it? I'll just get the grades
get into a good college a good job... Why should I waste my time learning
this?".

I used to gripe about the system whenever I heard that reply and why they just
didn't get it, but now I realize that they are simply reflecting society in
general. Most parents quite frankly don't care that they _know_ science or
anything as long as they get good grades. Most teachers hardly give a damn
about teaching and they aren't even remotely interested in science. Most
employers upon employment cannot check and do not look at how much the
individual understands anything. They just ask for a degree from a reputable
institute.

I admit that it is harder to change the mindset of a population, but this is
something that has to be done. Changing the school system and bringing out new
books will have limiting impact unless the foundations of this problem
(societies attitude toward learning) aren't addressed.

------
JshWright
An interesting topic, but I couldn't get more than a few paragraphs in. It's
really poorly written.

EDIT "couldn't" (I suppose if I'm going to gripe about grammar, I should at
least proof read...)

~~~
drats
I stopped reading at "Whatever you just said, it's wrong" as it was evident
from there that it was the usual HN hyperbole article. Not to say HN is
dominated by such articles, but their number has been steadily growing and one
is already too much.

------
superkarn
The analogy at the end (section IV) made the whole article easier to "get".

    
    
      ...an answer cannot be more precise than its data.  Or its question.

~~~
JabavuAdams
Except the example he gave was also wrong. 3 + 4.2 is 7.2, using exact
arithmetic, which should be the default assumption.

If you're measuring values under uncertainty, then his explanation makes some
sense. But that's a property of measurement and uncertainty, not of numbers or
arithmetic.

~~~
samatman
Default assumption for whom?

For a scientist, or someone working with real world data, this should never be
the default assumption.

Besides, in the paragraph with the arithmetic he explicitly talks about
significant figures. In context, the answer is unambiguously 7 .

~~~
djacobs
It's 7.2. Without context (and he gives none for the expression) everyone
(including me as a scientist) must assume abstract numbers. What's more, we
know he's not using measurements because there are no units...

------
sliverstorm
The example is not all that potent. before the link even loaded, the following
flashes through my head:

'well of course carbon from the air. ... oh, and water. They have a lot of
water.'

He tries to use something pretty clear cut, like mass and trees (mass is mass,
and trees are pretty typically also trees) as an analogue to something
inherently vague- psychiatry in this case. Whether someone is bipolar is way
more up to interpretation than whether something that weights 100kg has a mass
of 100kg or not.

------
frankus
Three vaguely related observations:

1\. When we lose weight due to eating right and/or exercising (excluding water
weight), it's because the air that we breathe out is slightly heavier than the
air that we breathe in.

2\. When we're burning wood in a fireplace, the heat it gives off is
essentially the sunlight that the tree has collected over its lifetime -- i.e.
the heat difference between full sun and the shade of the tree.

3\. A solar cell producing peak power is slightly colder than one that is
either open- or short-circuited.

~~~
a-priori
Re #1: You're ignoring metabolic byproducts that are excreted in urine or
feces or sweat. Are there any byproducts that are released in the breath?

~~~
frankus
I should have qualified that by saying it's true to roughly the same degree as
the claim that a tree's mass comes from the air. I.e. if you wave your hands
and ignore a lot of potentially-important second-order effects, it more or
less holds water :).

------
ErrantX
Excellent. After the first line I deliberately closed my eyes and tried to re-
reason it (and got it right, thankfully). It was quite refreshing to have a
blog post make you actually stop and _really_ think for a second.

The point was good as well. ;)

~~~
radu_floricica
It's the whole blog, not just the post :) Really worth bookmarking.

~~~
ErrantX
Damn straight. I just finished reading one of his latest entries; acidic,
critical and brilliant IMO.

[http://thelastpsychiatrist.com/2010/06/are_certain_behaviors...](http://thelastpsychiatrist.com/2010/06/are_certain_behaviors
--_and_jo.html)

EDIT: money quote: _The science error of our generation is this: If A is
strongly associated with B, and B is strongly associated with C, then A is
strongly associated to C._

------
Tichy
_stupid mode_

Opens up more questions than it answers. It seems when trees die, they become
earth or even oil. How come they don't completely dissolve into air again? And
if they don't completely dissolve into air, how come all the CO2 is not bound
in the earth yet (trees pluck it out of the air, then die and bind it to the
ground)? There would have to be bacteria or something that converts soil into
air (CO2), but then, why don't they dissolve everything?

~~~
gxti
Trees do dissolve. Forest fires are the most elegant way -- the reaction
liberates much of the carbon and all of the oxygen into gasses including CO2,
and the cycle is complete.

Bacteria that break down the rotting remains of a dead tree also consume the
energy stored in the cellulose and release gasses like carbon dioxide and
methane. At some point the remains don't contain bonds with easily freed
energy and you have regular old dirt. If they had a way to break down the dirt
further they would, but the cost is too high.

------
WilliamLP
Did anyone else think this was going to be about the Higgs boson?

~~~
metaxy
Higgs boson is also wrong. The biggest part of the mass is created by the
strong interaction between the quarks in the nucleon.

------
DarrenMills
I agree with the ultimate point in this article, but the way he got there
seemed to be rather jumpy. I also had a hard time following his train of
thought. I will say that the way the article ended was excellent.

------
Retric
This forget's about all the H as a tree get's most of it's hydrogen from
water.

EX:"Glucose" (C6H12O6) is from 6 * H20 + 6 * C02 => C6H12O6 + 6 * O2.

So a reasonable ansewer would be mostly air and water with some minirals from
the soil.

~~~
ErrantX
Uh, the second "section" on the page basically says about the same thing :)

~~~
Retric
_Some trees are more than 50% water by mass_

This is true, but missing my point. A lot of a trees weight is water but the H
in it's DNA is _from_ watter but not still water.

~~~
sliverstorm
Yes, and the question was where does the tree get it's mass from.

I suppose you could look at it in the twisted sense of 'what in the tree
contributes so much to it's mass', but that's a rather tortured use of
English.

~~~
Retric
If the meant "50% of the mass of some trees is from water" that then he should
have said so. _Some trees are more than 50% water by mass_ is a true
statement, but it means something else.

The author saying something related to the truth, but I think he has a poor
understanding of what is going on. Reading that I felt like a teacher who
wants to give some created for a student using the correct words while
realizing they don't quite get it.

As to precision it's more accurate to say 3 +/- 0.5 times 101 +/- 0.5 = 256.25
to 355.25 or 305.75 +/- 49.5 than to just say 300. For an extreme example (1
+/- .1) ^ 1,000 can be any ware from ~2.47e41 to ~1.748e-46.

PS: "Dead stars" is a reasonable if incomplete answer to the same question,
but context matters so it's not acceptable on a botany or chemistry exam. In
the same way that Air + Soil + Water would be missing the point on an
astronomy exam.

~~~
ErrantX
> As to precision it's more accurate to say 3 +/- 0.5 times 101 +/- 0.5 =
> 256.25 to 355.25 or 305.75 +/- 49.5 than to just say 300.

Ah, problem is you've changed the question now. Which is a reasonable thing to
do when face with 3 + 101.5 = ?, but not the point the author was making (or,
actually, it is the exact point the author is making) :)

~~~
Retric
Ehh, I was trying to show why "significant digests" are a poor approximation
of accuracy.

His explanation in terms of addition is incomplete. _Since "3" only has one
significant digit (3.03.0 is a more precise number with 2 significant digits)
the answer itself can have no more than one significant figure._ 3 +/- .5 +
101.5 +/- .05 = 104.5 +/- 0.55 which has 2 significant digits. Now in his
example 3 + 4.7 the three does limit the question to 1 significant digit, but
your example has more than that even though your also adding 3 to a number
(104.5 +/- 0.55)

PS: This is all assuming the accuracy based on the number of digits given you
could easily have 3 +/- .0001 and 101.5 +/- 70.

~~~
ErrantX
_PS: This is all assuming the accuracy based on the number of digits given you
could easily have 3 +/- .0001 and 101.5 +/- 70._

That is the whole point :)

------
millettjon
I had this same though recently after thinking about how much shrub/tree/grass
growth I have pruned out of my yard over the last 4 years ;-). Keeping a
compost pile of all trimmings keeps this in perspective. Conversely, the
amount of mass left after you burn wood is quite minimal. There was a nice
scene about that topic in the move "Smoke". Screenplay dialog here:
[http://www.script-o-rama.com/movie_scripts/s/smoke-script-
tr...](http://www.script-o-rama.com/movie_scripts/s/smoke-script-transcript-
paul-auster.html)

------
djacobs
As far as I know, most of the CO2 in plants goes to respiration for energy
production. Not saying it doesn't go to mass, as well, but it's the energy
side of things that people learn in elementary school.

We're not stupid, and this man needs to think about his accusations before he
blogs about them...

~~~
InclinedPlane
Are you aware that cellulose is just interlinked glucose molecules? A tree is
basically a giant hunk of hydrated sugar byproducts with some minor mineral
and other components.

~~~
djacobs
Yes, very. I could tell you all about the glycosidic linkages.

Some observations: Polysaccharides are not sugars. Mono- and di-saccharides
made of carbohydrates are. Glucose has other uses than becoming cellulose or
starch or glycogen. The life cycle of a plant is not linear or simplistic. CO2
is not only used as a substrate in anabolism.

------
jules
I asked this question to my brother who is in high school and he got it right
without me steering: CO2, water and a little bit from the ground. Education
works :)

------
shasta
Adam: Who invented the cotton gin?

Bob: That's easy, Eli Whitney

Adam: What's a cotton gin?

Bob: Shrug

------
cellis
I got the water part without even thinking, and photosynthesis danced in my
head as an answer, but carbon didn't even cross my mind.

------
splat
And here in the animal kingdom, when you exercise and lose thirty pounds, much
of that weight is breathed out.

------
ashutoshm
reminds me of Minds of Our Own
<http://www.learner.org/resources/series26.html>

------
TheLastPsych
As the author of the article, I thought I'd add my observation about the
comments here.

The point of my post was twofold.

First, an observation about what we think we know. When you say, "tiananmen
square massacre" to people, most have a basic understanding of what happened,
EXCEPT that the single image they have associated with it is the one of the
student in front of the tank. That incident happened, of course, but it was
the image selected to "teach" you about that incident, and that's what stuck.
1) This allows you to think you know something (one image), thought you don't
know really anything (what was the point of the whole thing?) 2) you know only
what someone else decided to tell you. If they had chosen to show you a pic of
a student dropping a hand grenade in a tank, well, there you go.

Second, the most pointed criticisms on this board come from scientists (e.g.
electromagnetic). This is because you're not relying on words, you're actually
trying to understand the process. Some will do it better than others, fine;
but my point was that most people are not taught that that process is
important, they are taught only to "know" things. In college I knew a guy who
could identify a lot (30?) dinosaurs. By name. Is he an expert? Everyone
thought he was.

Point: when I asked him what the modern descendant of the triceratops was, he
said it was a rhino. And no one disagreed with him, even after I pointed out
that triceratops laid eggs and rhinos don't. He didn't know that, but even
once he knew it it did not change his thinking; he was taught to think in
terms of names and appearances, and he applied himself accordingly. (I write
that story up, in case anyone cares.)

That he thought he was an expert is fine; that he didn't know dinos laid eggs
is also fine, but it is of importance to understand the divergence between egg
layers and mammals. That's where most people fail, and that's entirely the
fault of the way we learn: the news.

It's not school-- we barely remember much. But watch a segment on the news,
and you think you're informed, and then you extrapolate from that
"information" entirely on the force of prejudices you've acquired from
watching other news...

Who thinks China is mean to students? Ask around. Then ask them why they think
that. I hope it obvious that had the desire of the news media been to tell you
that the Chines govt. was nice to them...

I'm probably preaching to the choir here, but let me spin it around. While I'm
guessing most of you are technically oriented, how many would bristle if,
after a catastrophe, the government refused to send in crisis counselors and
mental health support people to the site? It's not been shown to be effective,
and could be counterproductive. But your intuition might suggest to you that
it should be done, and so the govt. is left defending itself. Or perhaps you
have a strong opinion on what Paulson should have done with AIG. Or whatever--
there is some field out of your expertise where you abandon your logical and
scientific mind, in favor of prejudice and presumption in the form of empty
words. And you don't know it.

The criticism that I am a poor writer is a common one. I know, I know.

I hope I made my point here (and perhaps enticed some readers?) without
offending anyone, which is something I try very hard not to do.

Cheers.

