Larry Osterman's WebLog

Confessions of an Old Fogey
Blog - Title

A Tree Grows... How?

A Tree Grows... How?

Valorie's currently attending a seminar about teaching science at the middle-school level.

Yesterday, her instructor asked the following question:

"I have in my hand a Douglass Fir tree seed that masses 1 gram [I'm making this number up, it's not important].  I plant it in my yard, water it regularly, and wait for 20 years.

At the end of that time, I have a 50 foot tree that masses 1,000 kilograms [again, I'm making this exact number up, it's not important].


My question is: Where did the 999,999 grams of mass come from?"


I'm going to put the answer out to the group.  Where DID the 999,999 grams of mass come from in the tree.

The answer surprises a lot of people.  And it brings to question how much we actually know about science.



I'm going to change my comment moderation policy for this one.  I'm NOT going to approve people whose comments have the right answer, until I post my follow-up post tomorrow, because once the right answer's been given, it's pretty clear.  But I'll be interested in knowing the percentage of comments that have the right answer vs. the wrong answer.


  • From the air.  The tree takes carbon from the air.
  • I would think it came from some combination of nutrients in the soil, carbon dioxide in the air, and water.
  • The air.

    More specifically, most of the tree is made from carbon fixed from the CO2 in the air.
  • If I remember my High School science correctly, the mass comes from the Carbon in the Carbon Dioxide it takes in from the air.
  • Mostly water I bet.  Probably some carbon from the atmosphere to make it burn later.  There's certainly some minerals and stuff from the ground, but if I remember 9th grade biology correctly, it's mostly water.
  • Mostly mass displaced by the root system?
  • God. It came from God. :)

  • We are all made of stars. :-)
  • Isn't it mostly water, carbon and nitrogen from the soil?
    Basically rainwater and dead plant matter.
  • Energy from the sun turned into mass via photosynthesis?
  • Carbon, from carbon dioxide in the air. It's an important part of the carbon cycle, and is the exact opposite of the release of carbon when fossil fuels are burnt (answering the question "why are ashes lighter than the wood they came from?" which plagued the philosophers who came up with the four-elements model of matter).
  • The majority of the mass comes from the air and the water.

    Photosynthesis converts carbon-dioxide from the air into oxygen and carbon. The majority of the oxygen is released back to the atmosphere, and the carbon is then combined with water to form various fibrous tissues (essentially long chain carbohydrates) that make up the cell walls. Also, the inner liquid of cells are (like animals) mostly water.

    There are of course other elements (phosphates, nitrogens, traces of sulphates and various metals) that are used as well, but the majority of the mass of a tree is carbohydrates and water.
  • It gets it's mass from:

    Water! (most of the mass is water, taken from the ground)
    Stuff from dirt! (disolved in the water, it takes in minerals & other nutrients from the soil)
    Air! (trees breath air, and the gases get used in the tree.)

    Of course, Water is far and away the largest contributor, behind that soil, and the rest is really far behind...

  • photosynthesis ?
  • CO2 from atomsphere during the photosynthesis process?
Page 1 of 7 (100 items) 12345»