[Lee]

why would increasing the co2 levels increase the rate of photosynthesis?

[Borek]

why would increasing the co2 levels increase the rate of photosynthesis?

What are substrates for the photosynthesis?

[savoy7]

Increasing CO2 may increase photosynthesis, but not the only factor.  The factors that are more important are:  temperature and certain wavelengths of light.

[savoy7]

also water is more important, because it can be a limiting factor.

[Mitch]

Write the balanced chemical equation.

[Donaldson Tan]

do you know the mechanism of photosynthesis? it's not just a mere 6CO2 + 6H2O -> C6H12O6 + 6O2..

photosynthesis reaction is divided into two parts:

1. the light reaction, whereby UV from the sun is converted to chemical potential energy in the form of excited electrons
2. the dark reaction, whereby CO2 is absorbed. the dark reaction is known as calvin cycle.

both the light and dark reactions occur independent of each other. the dark reaction consist of many sub-steps, enzymes and different sub-strate.

energy from the excited electron is converted into ATP at many sub-steps. Some of the ATPs formed is used to fuel the conversion of carbon dioxide to glucose.

the calvin cycle consist of carbon fixation (where CO2 is absorbed into the plant), PGA conversion and PGAL conversion. if you increase CO2 concentration, more CO2 will be absorbed, thus PGA and PGAL conversion occur at increased rate, so rate of sugar production increase. sugar production requires energy. the energy comes from sunlight (whose energy is harnessed via the light reaction). if there isnt sufficient energy available for reaction, then PGA & PGAL conversion occurs at a lower rate, thus sugar production rate decreases as well.

I hope this is sufficient to answer your question. anyway, i move your post to chemical biology.

[savoy7]

Lee
as one can see, this question actually can be quite consuming.

Geodome's last post was on the money.  Increasing Carbon Dioxide can increase photosynthesis.  There are a lot of factors that affect this though.  The power for the C4 (Calvin) or C3 cycle, which makes the glucose, comes from the photosystems.  The photosystems can be limited by temperature and water (along with light).  Chlorophyll has temp ranges where it works at an optimum level.  If you get out of those temp ranges, sugar production will be lowered.  Water is split by the photosystems and is essential part of the process.  If there is a drought, this will lower the amount of photosynthesis taking place.  These two factors (along with light) usually affect the rate of photosynthesis more than CO2 (because there usually is enough CO2 in the system).  

There has been a lot of research in this area over the last few years due to the attention global warming has been receiving.  Some research I was involved with deals with the effect of elevated CO2 levels on plants (in fact, on several trophic levels).  Besides CO2 levels being elevated, ozone levels have been rising.  What is interesting is the collabrative effects that occur when looking at both of these gases.  When combined, they greatly reduce the growth of trees.  Some of these studies are wrapping up this year.  The research was FACE research with the UW-Madison and MTU.  

Hopefully within the next few years, we have a better understanding of this process.