lesson
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If you look at a giant redwood tree weighing over two million pounds, almost all of that massive physical structure was built out of invisible gas pulled straight from the air.
In the 1640s, Flemish physician Jan Baptist van Helmont grew a willow tree in a pot for five years; the tree gained 164 pounds while the soil lost only two ounces, proving plants do not gain their bulk by "eating" dirt.
How exactly do green plants turn an invisible gas into solid wood, sweet fruit, and tough leaves?
Fixing Carbon from Thin Air
Carbon fixation is the biochemical process where photosynthetic producers convert inorganic carbon from atmospheric carbon dioxide (CO2) into energy-rich organic molecules (compounds containing carbon-hydrogen bonds).
Inside leaf cells, microscopic green organelles called chloroplasts absorb sunlight energy using the pigment chlorophyll, using that energy to split water and assemble glucose.
📊Interactive diagram
The overall chemical equation balances as: 6CO2+6H2OlightC6H12O6+6O2
Glucose is great for immediate cellular respiration, but a plant cannot survive on simple sugar alone. What happens next to all that fixed carbon?
Synthesizing Biological Molecules
Plants use the fixed carbon backbone of glucose (C6H12O6) as the fundamental building block to manufacture every major class of biological molecule.
To store energy compactly, enzymes link thousands of glucose rings into insoluble starch; to build strong cell walls, they link glucose into rigid cellulose fibers.
By rearranging the carbon, hydrogen, and oxygen atoms from glucose, plants also synthesize lipids (fats and oils) to store dense energy in seeds and construct cell membranes.