Transcript:

So, we're coming up in autumn, and the leaves are changing color to these brilliant yellows and oranges. So, what happened to the green? The green color of the leaf is because the chlorophyll molecule absorbs certain wavelengths of light. It absorbs the blues and it absorbs the reds and it reflects the green, which is why the leaf appears green. 

And as the season changes, there is a risk of freezing of the water molecule because the temperature is dropping. And photosynthesis cannot happen without liquid water. So the leaf has to do something with the chlorophyll molecule. Look at it. This is the chlorophyll molecule. It's expensive to make the chlorophyll molecule. It's a complex molecule. So what the leaf, what the tree does is it breaks down the chlorophyll, and all these sub parts of the chlorophyll are stored in the stem and the trunk of the tree so that they can be reformulated for the next year. 

And as the chlorophyll molecule disintegrates, the carotenoids kick in and this is a carotenoid. It's a C40 molecule, and the carotenoid absorbs blues up to greens and reflects reds and yellows, which is why the leaves turn color.