Originally posted by Big Mac
is there a way for photosynthesis to occur that would still produce the green colors found in the leaves?
sorry to appeal to the "pretty factor." but, perhaps the creator is creative as well.
Well, according to evolutionary theory, green is only comforting to us because we spent so much of our evolutionary history around green things. Green represents food.
From a physiological perspective plants are green because of the
amount of chlorophyll they contain. If they contained more chlorophyll, they'd be black. They aren't because the plant has evolved to minimise the carbon / nitrogen "cost" of producing chlorophyll, whilst maximising the amount of light harvested. The necessity for a light harvesting enzyme wouldn't change. Neither would the fact that most light isn't harvested, but instead goes straight through the leaf.
The biggest "problem" with photosynthesis is the ineffiency of the C-fixation process. The first problem the plant encounters is CO2 diffusion. Simply put, CO2 does not, most of the time, diffuse into the leaf quickly enough to saturate the carboxylating (CO2 fixing) exzyme, Rubisco. Secondly, diffusive resistances within the leaf exacerbate that problem, since O2 is produced in the chloroplast, leading to competition between CO2 and O2 for the Rubisco enzymatic site (Rubisco will fix both CO2 and O2). If Rubisco does fix O2, this leads to photorespiration, so the plant loses carbon. Also, and far worse from the plants point of view, photorespiration leads to the production of ammonia gas, which is a potential (and indeed, actual) loss of N for the plant. Since leaf photosynthesis scales linearly with N, this is a direct loss of future CO2 fixation.
These "problems" can be explained by the fact that Rubisco evolved in an atmosphere that was 21% CO2 and 0% oxygen. If Rubisco was produced by a divine creator, he;d have made it more efficient, both in terms of the aforementioned problems, and he'd have made it smaller (it is a huge protein, and due to it's catalytic inefficiency, is required in the leaf in huge quantities (~25% of leaf N)) and thus more efficient of resources.
[edit; a much better (at high light intensities) way of doing photosynthesis is by C4 plants (or CAM under drought), where CO2 is concentrated around Rubisco in special cells, called "bundle sheath cells" which are located close to the leaf veins (ready supply of water). CAM plants take up CO2 at night and store it as crassalacean acid (the CA in CAM, the M stands for metabolism). During the daytime, CAM plants release the CO2 into the leaf and fix it using Rubisco. Again, a divine creator would just make better Rubisco. The extra metabolism required for C4 and CAM is indicative of "tacked on" pathways, since the underlying chemistry is the same.]