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MIT student blogger Kim D. '09

Where do Trees Come From? by Kim D. '09

In my continuing quest to obtain a teaching certificate through MIT’s excellent STEP program, I am taking two teaching courses this semester. 11.125 focuses more on theory and 11.131 focuses on practical issues. For instance, 11.125 is more likely to talk about whether the tests you write for students are formative or summative, and 11.129 is more likely to talk about how to keep students from cheating on them.

Yesterday in 11.125, we talked a little bit about trees. As you know, they grow from seeds, much like this one.

Photo courtesy of

And of course if you wait a few years they get quite large…

Photo courtesy of

So, the question we were asked in class is, where does that huge increase in mass come from?

I want to hear your answers and reasoning in the comments… just think about it; no Wikipedia!

I also want your input on something else for 11.125. I need to sit in on some class at MIT as an impartial observer and take notes on how the teacher interacts with the students. Please look through MIT’s course catalog and let me know what classes interest you (and what you are wondering about them). I will choose one to check out and report back on it later!

30 responses to “Where do Trees Come From?”

  1. Answer Man says:

    It must be the CO2 in the air because trees are organic and therefore made primarily of carbon. They take the CO2 from the air and put it into other structures like glucose and starch.

    And you should check out Justice – because it sounds awesome.

  2. well from memory: you three are correct!

    This exponential increase in mass is a ‘complex’ combination of the three – water, light and CO(2).

    An intriguing question though, (especially because we’re not to use wikipedia) because one can easily look at trees and where they come from and say “Oh this is magic, how the heck did it get so big?”

    But like all things in physics – phenomena in nature is constant – a growth in an organism must have stemmed from somewhere (I guess we can call it ‘conservation of mass’ haha)

    Anywho, this question is synonymous to asking how humans move from 5 pounds to 130 pounds (no that’s not my weight, I only wish lol); but one can’t really say one answer, because its a combination of things. I can’t live without food, but I also can’t live without sleep, but I also cannot live without water and the list goes on!

    So there’s no one thing that caused the little bitty seed to grow into a great big tree.

    NB. you certainly can list what it needs but I do believe you’d have to write a book or else botanists (or whomever it is that studies the trees and their span) would be inessential!


    Captcha: ing rumnier (is that a new word for alcoholics? hehe)

  3. Rishi says:

    The vast majority of mass in trees comes from the carbon in CO2 (from the air). Bam. Science-ified.

  4. jamie '14? says:

    I’m no biologist, but it would seem to me as though this increase in mass is a direct result of the nutrients that trees absorb over time; so that would include sunlight, which is converted into energy through photosynthesis, and whatever else it absorbs from the soil

  5. Rishi says:

    Okay, true, the actual process of the increase in mass is due to a combination of light/water/CO2. But the actual mass comes from the carbon in CO2.

  6. Rishi says:

    Okay, true, the process of the increase in mass is due to a combination of light/water/CO2. But the actual mass comes from the carbon in CO2.

  7. Common sense would say to me: combination of water and starches/sugars/cellulose. The seedling takes in CO2 and water, photosynthesis happens, and structural materials are produced…the way they fit together (would the correct noun be “matrix”?) to form cells (which contain water, another big mass-giver) would create the mass. So it’s just the way the young tree takes nutrients and chemicals from its environment and utilizes them; it doesn’t create matter out of thin air.

    Could you tell us something about any classes at MIT that deal with machine cognition and/or neural networks, or even just basic neuroscience? I don’t know what classes exactly would deal with those (got to go do my homework; no time to check the catalog), but I’m really really interested in the mind/brain/reality/biology interface… raspberry

  8. Anonymous says:

    umm nutrients in the soil….

  9. It would be interesting to determine if a seed in a closed system with large, condensed amounts of carbon dioxide, sunlight, and water (proportioned, of course) could increase the growth rate of the tree, especially if the seedling was genetically modified to an extent. If this was applied to areas struggling with deforestation, we could replace the lost trees much quicker… Any comments on this?

  10. Caio '14? says:

    Water, CO2 and nutrients. The light triggers the photosynthetic reaction between CO2 and water, generating glucose that, when combined with the nutrients, generates ATP, then generating enough energy to duplicate cells and absorb more CO2 and water smile

    P/S: speaking of water, my captcha is “watery half”

  11. Upnorth says:

    Mass is conserved therefore the increase of the mass of the tree comes from everywhere!!! =P

    Recaptcha is “Daintier by”…

  12. God made it so. End of story, no other logic, science, reason, or facts matter, even if completely impossible to disprove. My 2,000 year old personal belief system is true.

  13. Anonymous says:

    I love how I was responsible for the whole “tell us what the captcha thing said” thing.

    here is the original post…

    I got 3 Ds in my junior year, including math and chemistry, and I’m applying anyway (senior)
    TRUE, I’ve also published artices on neuronanotechnology, have worked with several top level scientists, have an IQ of over 170 (started talking at 9 months) and generally believe I’m of the sort appropriate for MIT.
    I do not believe MIT looks at the simply the “numbers” for academic achievement, which are meaningless indicators of true intelligence and intuition.
    Its not about what you’ve done, but rather, what you WILL do.

    (p.s…. the Ds were as followed:
    class participation-0%
    tests-105% (there were also 5 extra points available)
    never picked up the book once.

    p.s.s…the catchpa word was “rupee”, if thats a coincidence…

    Posted by: Mike on January 12, 2010 02:47 PM

  14. Arpit says:

    Mass is certainly not created since this would violate concepts of conservation of mass. The gain in mass must be due to cell multiplication and accumalation of glycogen(is it glucose? something like that) prepared by photosynthesis (which requires CO2, water,sunlight)

  15. It must be CO2 in the air.

    Now the mass increased is mainly lignin, or in other words, cellulose. Cellulose is a carbohydrate, which basic unit in plant is glucose. Glucose is synthesized from light (light carries no mass in non-relativistic sense), water and CO2. The oxygen atoms in the water molecules are removed and released into the air, only the hydrogen is retained. The mass of hydrogen is so light that CO2 counts much more.

    Conclusion: CO2.

    [Correct me if I’m wrong: I am not taking a Biology class this year raspberry]

  16. Anonymous says:

    i’m really interested in course 16- aeronautics and astronautics so would love to know more bout it.. especially the difference between MIT’s course and that of other colleges worldwide.. thanks a bunch

  17. Morteza says:

    Obviously it comes from the air and the earth. Carbon from air (in form of CO2), Nitrogen from the soil (in form of Nitrite) and Oxygen from both water and CO2 (CO2 and water makes Glucose and O2, O2 is released but a Glucose have 12 Oxygen atoms too). Other minerals come from the soil too. The mass of the tree is mainly due to Carbon and Oxygen. Sunlight is just energy.

    I think teachers should be like farmers. As farmers just help trees to get their needs from their surroundings (Of course they some times give fertilizers to them but not always) teachers should just help students to get knowledge from other sources in most cases and give them direct informations just in special cases.

  18. Zeki('14?) says:

    It is about hard cellulose walls of plant cells.Photosynthesis helps cell create harder walls but a very fast mitosis in cells helps the tree grow up.For mitosis,cell must be bigger than nucleus can manage,must have 2 times more DNA than needed and r3/r2 must be too big for cell to cary.These can be done by ATP synthesis so respiration helps more than photosynthesis.I mean oxygen and nitrogen in the air.For all these we need too much matters.They mostly come from nutriants from soil some with active and some with passive transmission.For active transmission we need ATP again.And all those matters create a huge tree.Why does a plant do this?I think it comes from a little interaction between two atoms.First they affected each other and it keep on till an organism.It was a huge coincidence but didn’t happen in one day.It will go on untill perfect organism.

    recaptcha:quality people’s

  19. Zeki('14?) says:

    I feel like in highschool again after I wrote that.Thanks for making me feel 2 years younger smile

  20. Deb says:

    The trees absorb CO2 from air, water from the ground and produce glucose in the presence of sunlight. This glucose results in the increase in mass

  21. fox says:

    hmm… In simple words, I guess it’s mostly water, CO2, and sunlight as energy. And of course small amounts of minerals are also taken from soil.

    What’s really interesting for you and me in that process – The huge amount of carbon that’s put back to earth during a tree’s life!

  22. Hello Kim,
    Well its a good Question ! Where do trees come from?

    Such huge masses of life !
    Well, I must say, Living organisms (lets say trees for that matter) are a unique state of matter in which it interacts with itself and energy ( so called) and with other matter to make the Organic reactions or the Bio- Chemical reactions and processes to undergo Spontaneously (by itself) on the whole, within the controlled environment of those reactions which itself is controlled by those reactions !! Life is like a chain reaction or many chain reactions which molecules present in universe undergo to constitute the living state !

    So sticking to books, the organic matter of the trees is basically carbon, water and to run those reactions to put all together to react, they need nutrients !

    So, all life (say trees) is derrived from non living matter when a nature sets conditions to start those spontaneous reactions !

    Everyone knows the initial spark to start these reactions on earth originated about millions of years ago !

    We are (trees for that matter ) all Stardust (originated in the Big Bang) ! raspberry
    Somehow nature has in billions of years, has engineered its technology, and made living creatures to harness the energy, that we plan to harness for advancing our science and technology !

    I certainly hope someday I will join MIT to find the answers !

    Sambheet Krishna
    Class Of 2014

  23. hcs says:

    From memory, I’m pretty sure it’s water. (as with humans, actually, although not in the same way)

    reasoning: well, it’s not dirt, because otherwise the dirt would disappear. it’s not “the air” (although some of the mass probably comes from the carbon in the CO2 the tree absorbs), and the only other option is light…

  24. ymous says:

    It’s obviously the light!

  25. ymous says:

    Why else would trees have color?

  26. Neptunium says:

    Organic molecules (carbs, fats, proteins etc.) are largely composed of carbon, hydrogen and oxygen. Carbon is from CO2 in the air which the plants use to produce sugars. Hydrogen is from H2O in the soil, which is why we must water plants. And the oxygen…well I guess it could come from either or both CO2 and H2O…but I don’t know the rxn mechanism for photosynthesis.

    The proteins in the plant cells also contain nitrogen. This nitrogen is from the soil because plants can’t use atmospheric nitrogen. It is found in fertilisers (such as ammonium nitrate), that is why we add fertilisers.

    Apart from these 4 main elements, plants also contain traces of mineral such as iron, magnesium, etc.

  27. @ Neptunium: I think the oxygen comes from the CO2. But this is just from my Grade 11 Biology (which can be quite wrong.)

  28. QA ('14?) says:

    Must be water since those trees never pee you know. lol smile)
    Anyway, everyone probably knows that water evaporates through leaves. So where is that huge mass from???
    I’d say it’s kinda the combination of everything. According to the chemical equation inside the tree, in order to produce cellulose (didn’t look up in the Wiki, just my English dictionary for spelling check raspberry), it needs water, nutrition, light, etc. And it does take time to achieve that (one by one particle wink ). Therefore that why trees don’t grow up (nothing lively in this world does)in 1 day or 2.
    Hope this helps :D

  29. @ Kenneth
    The Oxygen comes from the Photolysis of H2O (Water) and not from the CO 2(Carbon Dioxide) in Plants.

    Well, for why trees are so huge, I have already given the answer above.

  30. Adam ('14?) says:

    I second “Interested in Biology” in support of neuroscience/machine cognition classes.