What happened to the leaves Baba?

"Baba, what happened to those leaves?"
I explained that they changed color. Why? Why? Why?
"Well to know the exact reason I think we have to look it up together."
Then suddenly as I continued to walk down the sidewalk to the T station that word popped into my head. "Chlorophyll. That's right." I explained to Noah. "Chlorophyll makes the leaves green....." anyway, so I decided we would look it up together. Maybe watch some PBS special about it.
I recall watching a nature special about how plants actually do respond to their environment much more than we used to think, but that they just take longer to respond. For instance they showed two flowers growing.. sped up, and it was clear when seen fast forwarded like that that the flowers were competing for sunlight, battling, moving back and forth as if they were doing some sort of push hands where you don't touch.
There was also the wild tobacco plant that produced something sweet for caterpillars to eat, but that made them release an odor that gave away their location to predators. A sort of trap. Anyway, I'll try and see if Noah will watch that episode with me. He may not like it all that much, and I guess it doesn't exactly have to do with the leaves changing color.