Aang is practicing his airbending skills for his huge fight against the Fire Lord, but he needs to know how to harness water from the grass so he can waterbend. To do that he has to know about photosynthesis.
Because there is so much information on photosynthesis and not enough time to go into depth of it. Katara explains it as if she were talking to a five-year-old. Time is of the essence here.
"Plants breathe in the carbon dioxide in the air, which goes through the stromata by the way, and releases oxygen. So when you try to waterbend you have to think about your breathing. Really try to connect to your surroundings, the life that is around you. This all occurs in the chloroplast, by the way," Katara explained.
"Now that you have accomplished breathing, you will now incorporate water!" says Katara. Katara goes on to explain that plants absorb water through the roots and that they trap sunlight for energy. Aang wonders to himself whether this is relevant to water bending and defeating the Fire Lord. But he reminds himself that Katara lived in the Ice Pole and didn't get to see plants growing up.
Katara finally gets back on track and they begin waterbending. All that talk about plants really was irrelevant. "Did you know that plants use glucose to make cellulose and starch? OH! I almost forgot the chemical equation!" Katara is becoming annoying.
THE BATTLE BETWEEN THE FIRE LORD AND AANG BEGINS!! IF AANG WINS, ALL FOUR NATIONS ARE SAVED!
6H20+ 6CO2+Energy - 6C6H12O6+602 This is the chemical equation!