Whilst browsing the thumbnails of the images for this challeneg I didn't really pay this much attention which is a shame as its a really great shot and you need to see it at full size to really appreciate it. What I like is how you have linked the challenge of chemistry with the title and concept of your image, photosynthasis. But how to display this invisible chemistry in your photo? The vibrant saturated greens are a great way of doing this but what I like more than that is the backlighting which focuses attention on the minute details within the structure of the leaf. I hope people don't overlook this as it so beautifully illustrates the concept of photosynthesism, and the rim light around the outside of the leaf is an awesome touch.
Technically.. well, that shadow isn't doing you any favours, it really competes for attention and in this image particularly you need to avoid that at all costs. I would have liked to have seen a slightly different composition - the same effects in play but closer up with maybe not the entire leaf showing and some of that great bokeh in the background. Overall, I like this one and have given it an 8.
This might be very picky on my part, but photosynthesis to me will always be biology, not chemistry...
Apart from that, I quite like the image - though I find the out of focus leaf halfway down the left side of the picture a little distracting.