Part of Richard Feynman's "Fun to Imagine" series, I think. Video link: https://www.youtube.com/watch?v=P1ww1IXRfTA

Plants can often be understood as pumps that pull water from the ground to combine with atmospheric CO2 and sunlight to make sugars that they recombine to make more of themselves.

I felt somehow betrayed when I learned that the oxygen trees release comes off the water that's used for photosynthesis, and not the carbon dioxide directly.

(Of course, the oxygen in the carbon dioxide ends up in new water molecules in a later step of photosynthesis, and that water either immediately or eventually finds itself in another photosynthesis reaction, so that carbon dioxide oxygen finds itself released into air sooner or later, but still.)

And when you lose weight it's mainly in the form of exhaled gas.

I like that a lot! I will remember it next time I’m willing myself not to stop.