Today there are some theories about what that function might be. It'd be like spending money to, I don't know, to have your old car repainted when you know the car's not going to last more than a couple of months.All this extra anthocyanin in the autumn seems like a waste.But remember, nature is very economical with its resources, so that means anthocyanin must be serving some function that's important for the tree. Why would a tree produce more anthocyanin just before dropping its leaves?Why does the tree spend so much of its resources doing this just before the leaves fall off?On the surface, this doesn't make sense.

Here's where the classic explanation doesn't seem to apply to red.What's interesting is that during the summer, there was very little if any anthocyanin in the leaves, but in the weeks before a tree is about to drop its leaves, the production of anthocyanins increases significantly.In other words, unlike those other pigments, anthocyanins are not just unmasked by the breakdown of chlorophyll in autumn they're actually created at this time. Just what produces this red color in leaves? It's a red pigment called anthocyanin. It was there in the leaf all along but it was hidden by the green chlorophyll.OK, so that's the classic explanation, and it's partially right.Why do I say 'partially'? Well, it's probably true for pigments like yellow or orange, but it doesn't seem to hold for the red pigment.Let's back up a bit. Since chlorophyll is sensitive to sunlight and to cold temperatures-both of which you get in autumn-the existing chlorophyll in the leaves breaks down.And since it's not being replaced by the new chlorophyll, the green color of the leaves gradually fades away.As this happens, the other pigments present in the leaf become visible.According to the classic theory, this is true for the red pigment as well. The chlorophyll in the leaves collects energy from the Sun, in the form of sunlight, and it converts this energy into sugar, which is food for the plant.It's chlorophyll that makes leaves green most of the time.Now, the classic explanation for why leaves change color is this: in autumn, the leaves start preparing for the winter and stop synthesizing new chlorophyll. Well, before we discuss why leaves turn red, first let's, um-look, I know this is very old material, but just to play it safe-let's first go over why leaves are usually green.It's chlorophyll, right? Leaves get their green color from chlorophyll-the chemical that's responsible for photosynthesis. to yellow, orange, and lots of other colors.So this'll be a great time to talk about how and why some of these leaves turn one color in particular-and that's bright red. FEMALE PROFESSOR:It's autumn, and as you know, in most parts of the United States the leaves on the trees are changing color from green. NARRATOR:Listen to part of a lecture in a botany class.

Why the website for tpo toefl is down