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Biology/flower morphology

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Question
This is a question from the USABO 2011 open exam.
Suppose you are walking through a deciduous forest. You notice a dead tree that had been cut down and cut into logs that were tagged and labeled for removal from the forest three years prior. You and a friend try to move one of the smaller logs in order to build a camp fire. You find that the small log is heavy and difficult to move. The mass of the log is actually made-up mostly of:
A. Water from the soil
B. Macronutrients from the soil
C. Micronutrients from the soil
D. An invisible gas from the air
E. Membrane-bound cell organelles of the prokaryotes

The correct answer is D, but I don't understand why the answer is D and not E or any other choice.
Thanks!

Answer
Hi Tessa
This is puzzling to me also. Air consists of over 90% Nitrogen, oxygen and carbon dioxide and the mass of wood is secondary xylem tissue. It is mainly Carbohyrate and lignin. The only conclusion I can come to is that the reference is to the hydrogem in a carbohydrate molecule which of course is no longer a gas. Let me know if you find out  

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Walter Hintz

Expertise

Science teacher for over 50 years. MSc. in biology. I can answer questions in general biology, zoology, botany, anatomy and physiology and biochemistry.

Experience

I have a MSc in biology and have been a science teacher for over 50 years. At present I am a faculty member at a college and a science consultant at seven catholic schools.

Publications
The Ohio journal of Science
Momentum-The Journal of the Catholic Education Association

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