November 18, 2008

Where Does A Tree Get Its Mass?

Whatever you just said, it's wrong.

A tree starts out as a seed.  Where does it get the mass? 

The common answer is: from the soil, which is wrong. 

The mass of the tree comes from the wood (cellulose), and cellulose (by weight) is carbon.  Carbon comes from the air (CO2).


The first question you want to ask, right now, is why this now obvious answer wasn't obvious to begin with.  More specifically, why you know the word "photosynthesis" but not how to apply it, at all.

Why were we taught photosynthesis?  First, most of us don't remember anything about it  anyway.  If we do, we have recollections of certain unconnected concepts:

  • sun gives "energy"
  • plants "take up" "sunlight"
  • they "breathe" CO2 and "release" O2
  • It's good to talk to plants

The quotes serve to suggest we don't even really know the meaning of the terms we learned.

None of those statements are informative, nor can the be applied to reality (e.g. answering the above question.)  It's not that you forgot; it's unlikely you could have answered that question even back when you were learning photosynthesis.

Yet-- and this is the point-- the word "photosynthesis" is in your head. You learned a made up word, an artificial carve out of what is really a fluid physical process.  You didn't learn any of the reality.

So, on the one hand, we actually didn't learn anything.  And, on the other hand-- the worse hand-- we actually think we know something.  Not just ignorant; but ignorant and deluded.


But "tree mass comes from the air" isn't actually right, either.  Some trees are more than 50% water by mass, so the mass of a tree would indeed come from the ground.  (No partial credit: if you said "from the ground" but were thinking "minerals" you were still wrong.)

Indeed, this question reveals that even with a general background in science, and two acceptable answers, most people still get it wrong.  So what, exactly, was the point of the general background in science, let alone photosynthesis?

In other words, you don't really appreciate that a) a tree has water mass; b) air has mass.

I state it here, and you "know" it, but that's not the same as it being a fundamental part of your worldview, the way "the sun is hot" or "the earth revolves around the sun" does, fundamentals that allow you to make guesses about reality.  That's what science should have given you; instead, it gave you a hodgepodge of disconnected linguistic propositions that neither describe reality nor predict reality.  

"Where do plants get their energy?"  "Photosynthesis."  Nothing happened there, except words.

Here's an example: if, prior to this post, I had asked why a helium balloon, despite weighing something, floats, you'd have to reason out an answer.  But just my saying, "air has mass" makes the question easier to answer.  You already know air has mass, you don't need me to tell you; but you don't feel it-- that's why my telling you here makes a difference.

I hardly need point out how a discussion about global warming is vastly altered if it is intuitively understood that trees get their carbon from the air.


But, actually, both of those answers are wrong: the question itself is meaningless.  It is too vague, allows for multiple different interpretations and answers, is simultaneously misleading and oversimplified.

The bigger problem-- and this applies not only to science but to any field furthered by a dialectic-- is that we demand precision in answers, and allow-- expect-- imprecision in the questions.

"Where does the dry mass of a tree come from?" would be a little better.  Etc.  But no one worries about this; indeed, many shrug their shoulders, "yeah, the question is vague, but we all know what it means."  Well, evidently not.

It barely requires exposition that psychiatry suffers greatly from this problem, the haziest and laziest of terms and definitions magically generating concrete and specific responses.  Internist asks me, "I have a patient who is bipolar, what should I do?"   If I say anything other than "Depakote" or equivalent, he thinks I'm being an ass.  But my answer is 100x less relevant than understanding what he means by either "bipolar," "patient," or "do."

Politics, I need not point out, is worse.  The most asinine questions are expected to generate meaningful responses.  "Should we bail out General Motors?"  Which one of those words actually means what you say it means?  Who is "we?"  What's a "bail out?"  "General Motors" the whole company, the pension division, the new plant they opened in Russia, what?   But if you ask for any clarification, you're being difficult.  You don't get it.


A final analogy may be here helpful.  You may also (not) remember from school "significant digits."    For example, 3 + 4.2 = 7.  Since "3" only has one significant digit (3.0 is a more precise number with 2 significant digits) the answer itself can have no more than one significant figure.  Importantly, it's not that "7" is an okay answer, but really 7.2 is more precise.  7.2 is wrong, because that 3 could have been 3.4, 2.6, etc. 

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

The first business of science education should not be to help us answer questions, but to help us ask questions.


This is such an important c... (Below threshold)

November 18, 2008 8:07 PM | Posted by Sohaib: | Reply

This is such an important concept for people to learn that an enormous number of even intelligent people don't get. The following two posts by Eliezer Yudkowsky make a similar point on the overcoming bias blog:

Fake Explanations:

Mysterious Answers:

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I knew the right answer, bu... (Below threshold)

November 18, 2008 9:19 PM | Posted by Fargo: | Reply

I knew the right answer, but only because I studied in a class on biotechnology for four years.

Yesterday I was at a client's, one who is intensely religious and intensely right wing, and he's going on about the economy. Finally he looks at me and says "You know what's causing all this recession, right?" to which I wanted to reply "No, actually I only have the vaguest fucking idea how something like this happens, and what little I can say I understand comes from a Tom Wolfe book I didn't enjoy." but instead nipped that to a simple no.

I half expected him to fly his true colors and say gays or Jews, but instead he blamed it on the upswing of oil prices. He seriously seemed to believe that this one thing could have caused this, all on its lonesome. Naturally it was preceded with one of those statements you learn to be an indicator of something stupid about to be said- "I don't claim to be the smartest man in the world, but it's pretty clear to me...".

Of course, this same guy once launched into how the earth isn't as old as we think it is, because it was "proven" that the speed of light isn't a constant, invalidating carbon dating.

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Where does a tree get its m... (Below threshold)

November 18, 2008 9:26 PM | Posted by Flinthart: | Reply

Where does a tree get its mass? Current theory suggests that mass is a result of the (still undetected) Higgs Boson, interacting in some not-yet understood means with the fundamental fabric of the universe. Because we don't understand that interaction, we call 'mass' a basic property of matter.

And you, sir, are a pompous poseur: a statement I believe to be both precise and accurate.

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dugg. and i agree with the ... (Below threshold)

November 18, 2008 10:21 PM | Posted by the0ther: | Reply

dugg. and i agree with the first commenter. ob is a fantastic blog that talks about this type of thing quite frequently.

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"And you, sir, are a pompou... (Below threshold)

November 19, 2008 12:27 AM | Posted by Diego: | Reply

"And you, sir, are a pompous poseur: a statement I believe to be both precise and accurate."

Mr Flinthart, could you please elaborate on your affirmation? Your previous explanation is just a valid answer to one of many ways of taking that question. I could tell you you're right, as I can tell you you're wrong, but that's not the point.

The point here is "Why is that the question", "what does it entail" and "what would be the right answer based on those facts" if there was any question at all. Those set the question in a context where it can be studied and thus a correct procedure can be followed.

Maybe asking you "Where does a tree get its mass" leads to nowhere in the current economic situation. "Why is there an economic recession" would be a question, if we knew exactly what a recesion entails and thus what we are asking. The problem is that in the midst of all these naming process, there are certain disconnected facts that carry significance that can't really hold upon themselves because they are general terms that may or may not even apply at all to what we want to solve, or at least in the way we wish they would, hence, the question about bipolarity, which, in itself isn't a simple diagnosis.

Sorry, english isn't my native language.

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You guys are a lot more fun... (Below threshold)

November 19, 2008 7:01 AM | Posted by varangianguard: | Reply

You guys are a lot more fun than politicians. Depending upon what my meaning of "fun" is I suppose.

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I did know that air has mas... (Below threshold)

November 19, 2008 10:03 AM | Posted by Chris Jones: | Reply

I did know that air has mass, but obviously not in a way to correctly answer the question, yet also not only in the facile "helium floats" way that you suggest.

I began cycling competitively this year (triathlons, actually), and it is impossible to develop even a superficial understanding of the importance of aerodynamics without first grasping the basic fact that air is "in your way". When riding, I still imagine myself knocking millions of "bits" of air out of my way, like tiny bowling pins.

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I'm not surprised that Yudk... (Below threshold)

November 19, 2008 1:15 PM | Posted, in reply to Sohaib's comment, by FunkStyles: | Reply

I'm not surprised that Yudkowsky has some good things to say on the subject. Considering the amount of time that he's put into breaking down the idea of intelligence, he'd damn well better have some good insight, eh?

Honestly, I think everyone should at least try to work through Levels of Organization in General Intelligence. It's pretty powerful stuff.

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Is it weird that, when I fi... (Below threshold)

November 19, 2008 4:12 PM | Posted by Fnord: | Reply

Is it weird that, when I first read the title, I thought you were asking which Catholic priests minister to trees?

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Nicely asked and illustrate... (Below threshold)

November 19, 2008 7:46 PM | Posted by h2odragon: | Reply

Nicely asked and illustrated. You might then go on to ask, in the face of imprecise questions, "why has this been posed to me in this way?" and perhaps speculate as to the motives of the questioner...

I'd love to bail out GM, if it means I get a free Corvette that my kids' grandchildren have to pay for. What are childrens for if not to ensure our own comfort and enjoyment?

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I'm happy to see another po... (Below threshold)

November 20, 2008 2:59 AM | Posted by David: | Reply

I'm happy to see another post along these lines of "what the #@!%#?" It's taken me well over a day to conclude I don't even have enough of a POV to pose a question, well asked or not.

For some unfathomable reason, I look forward to your next post. Seriously.


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I may have been reading too... (Below threshold)

November 20, 2008 2:05 PM | Posted by spriteless: | Reply

I may have been reading too long when I saw that question and though: Last is asking a trick question again.

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The real question is where ... (Below threshold)

November 20, 2008 2:52 PM | Posted by Anonymous: | Reply

The real question is where did my cock get its mass? Answer? A gift from the heavens above. The chicks dig it.

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As Will Rogers is supposed ... (Below threshold)

November 22, 2008 12:37 PM | Posted by Aaron Davies: | Reply

As Will Rogers is supposed to have said "It's not what people don't know that hurts them. It's what they do know that just ain't so." I suggest this as a motto for your blog, in the event that you get tired of people asking you what the German means. It's particularly appropriate in that I can't find evidence he actually said it…

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Feb 19 09 Reuters news stor... (Below threshold)

February 19, 2009 8:48 AM | Posted by Anonymous: | Reply

Feb 19 09 Reuters news story: with all of this available carbon, trees are getting bigger:
this link may work for a while

Otherwise google "Forests absorb 20 percent of fossil fuel emissions: study. Michael Kahn."

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The problem seems like lang... (Below threshold)

March 16, 2009 8:24 AM | Posted by hegemonicon: | Reply

The problem seems like language isn't designed for this kind of precision. We have thousands of words that are meant to define things specifically, but they REALLY just relate a particular word to something you've experienced. Since everyone's experiences differ slightly, the meaning of words will differ slightly between people.

For some words the difference will be infintesimal or non-existant. Everyone has basically the same experience of the sun, so the word 'sun' is more or less the same for everyone. Its directly related to an experience. So is 'fire truck'. But things like 'life', 'mass' are more abstract, and can't be directly related to something in the world. You have to assemble several different ideas together to get their meaning. As words get more abstract you have to relate them to more and more experiences to get their meaning, and so their use will differ more and more between people.

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I think your suggestion tha... (Below threshold)

June 23, 2010 5:16 AM | Posted by jake fontenot: | Reply

I think your suggestion that "'from the air' is wrong" is obtuse and asinine. I've never hear anyone answer "water from the ground. Trees are made of water". Sure if they did, a follow up of "well...beyond water weight" is in order, and the imprecision of the question is exposed...but you're missing the point. I think the vast majority of people are well aware that both plants and animals contain water, and that water has weight. People 'get' the question. Precision is not an issue. It's an utterly simple and basic question that almost always generates a moment of unexpected reflection whenever it's first heard. It's elegant, if you ask me.

Also, your statement "Carbon comes from the air (CO2)" is both inaccurate and ridiculous.

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The carbon that comes from ... (Below threshold)

July 1, 2010 4:31 PM | Posted by DJ: | Reply

The carbon that comes from the air (CO2) contributes to plant energy for most of its life and only gives it mass for the period of time when it is adding mass (obviously). You could say the primary purpose of photosynthesis is energy production, and it is the energy principle that people learn in high school. Those of us with higher degrees in bio definitely understand that CO2 can be used as a carbon source, but we also know that a very important part of photosynthesis is the production of energy for anabolism.

Please stop being so condescending.

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@hegemoniconI gene... (Below threshold)

July 1, 2010 4:34 PM | Posted, in reply to hegemonicon's comment, by Anonymous: | Reply


I generally agree with that premise, but not here. Mass is both a defined concept in science and a deeply universal and intuitive experience that most of us (even across cultures) agree on.

I do not usually believe in universal concepts, but mass is one I think defies cultural boundaries.

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even with whatever backgrou... (Below threshold)

July 1, 2010 4:46 PM | Posted by Newt: | Reply

even with whatever background you have in science, and two acceptable answers, you still get it grossly and arrogantly wrong.

Cellulose isn't made entirely or even mostly of carbon. It's a carbohydrate. What else is in cellulose? Where do you think that comes from?

It can be a meaningless question and your showy droning can still be wrong.

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The goal here is unconditio... (Below threshold)

July 1, 2010 5:08 PM | Posted by Sam Pearson: | Reply

The goal here is unconditioned experience, which is experiencing reality without attachment to anything nor aversion to anything.

To hold science up on the presupposition of consciousness, and THEN to make claims, hypotheses, theories, and measurements BASED on that very presupposition with ZERO proof of consciousness is precisely the same as holding a presupposition of an omnipotent deity and then making claims, hypotheses, theories, and measurements based on that.

If you say "I am conscious because I am conscious," or "I think therefore, I am," your statements are completely devoid of semantic content. They, being absolutely devoid of semantics, have zero inferential power. Neither do they prove anything nor do they disprove anything. You may as well have said "This vreek here has tremelz bopahkun!" What can we possibly infer from that, that isn't itself semantically null?

True science is the investigation of all its foundations and assumptions, all the way down. If no semantic foundation for science exists, the entire house of cards collapses. And yet we continue to assume certain truths based on zero evidence.

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If CO2 contributes to plant... (Below threshold)

July 1, 2010 5:20 PM | Posted, in reply to DJ's comment, by Jeremy Leader: | Reply

If CO2 contributes to plant energy, and the plants transpire O2 as a waste product, where does the corresponding carbon go? I don't believe plants transmute the mass of entire carbon atoms into energy.

It's possible that it goes somewhere other than into the mass of the plant, but it's been several decades since my last formal biology class and I can't imagine where else the carbon would go. My best guess is that it if it doesn't contribute to the mass of the tree, it goes into the mass of parts that are eventually shed (leaves, needles, etc.).

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3 + 4.2 = 7.2</stro... (Below threshold)

July 1, 2010 5:23 PM | Posted by DJ: | Reply

3 + 4.2 = 7.2, period.

Significant digits are only relevant at all when you're dealing with measurements, not abstract numbers.

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My point is not</st... (Below threshold)

July 1, 2010 5:26 PM | Posted, in reply to Jeremy Leader's comment, by DJ: | Reply

My point is not that CO2 doesn't go to mass. My point is that the education he's referring to, where most people learned photosynthesis, does not teach what he claims it does. Instead, it only teaches students about the energy side of things. The bigger, more solid pictures comes later. Not everyone has to take high school biology, and we are not all imbeciles who don't understand what we say. I don't know many people who use the word photosynthesis without grasping what it does.

(Maybe that's how it is in psychiatry, I don't know...)

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:-)Why do things f... (Below threshold)

July 1, 2010 6:09 PM | Posted by Alok: | Reply


Why do things fall? They fall due to gravity! ;-) It's the same story everywhere. Some of us who are termed the smarter ones, I believe are the ones who were/are able to see through these things and figure what was really going on. I only even asked this question (tree mass) only after reaching adulthood.

Back during childhood days we were told (a hundred times so we could memorize) that plant cells have a rigid cell wall while animal cells don't (for all readers thinking of exceptions to this, just let go). I did not at that age connect this with plants not being mobile while animals run around. So animals have flexible bodies and bones/joints for rigidity. (Is this correct by the way? Why cannot plants be mobile while still having rigid cell walls?) See, I do not know, and I blame the quality of education.

Here is another question I ask that I do not have the answer to. Why did nature not create animals that do photosynthesis (OK, I myself know of some exceptions this time from the microbial world). I think the answer lies really in numbers. Photosynthesis does not generate enough energy for the functions that animals do (being mobile and carrying a brain on them while still not having as much surface area as plants). Can someone please point me to calculations showing this, if correct!?

The thought I then have is, what is the solution? How explain to people unfamiliar or to kids so as to maximize what they absorb. I always get the blame of overloading kids with complexity whenever I try to explain them something (while I am internally swearing to myself that what I am explaining cannot be any simpler).

Feynman talks about this issue at length in "Surely you're joking", but I do not remember him supplying an answer really.

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what an obnoxious post. wh... (Below threshold)

July 1, 2010 7:05 PM | Posted by roadnottaken: | Reply

what an obnoxious post. why assume that nobody knows the answer to this question? I'm sure some people didn't know the answer, but others (myself, a biologist) do and the tone of the whole article is just arrogant and insipid.

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I half expected h... (Below threshold)

July 1, 2010 9:54 PM | Posted, in reply to Fargo's comment, by wcoenen: | Reply

I half expected him to fly his true colors and say gays or Jews, but instead he blamed it on the upswing of oil prices. He seriously seemed to believe that this one thing could have caused this, all on its lonesome.

I wouldn't be so quick to dismiss this hypothesis. It seems reasonable to assume that economic growth relies on cheap energy. Even lacking a good model, we only need to examine history to see that jumps in oil prices seem to go together with recessions.

In fact, just before the subprime mortgage crisis hit some people were wondering why the jump in oil prices wasn't causing a recession that time around. Turns out they spoke too soon.

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1) I doubt most people thin... (Below threshold)

July 2, 2010 12:29 AM | Posted by Anonymous: | Reply

1) I doubt most people think that the mass of a tree comes from the soil. It's generally well recognized by anyone with a television or a computer that organisms are predominantly made up of water. Anyone who has seen a commercial for hand lotion knows the "human body is 70% water", thx lubriderm brand lotion. Generally a field with plants doesn't become devoid of soil. People probably do not htink plants are built from soil