Re: How long does it take for the light reaction of photosynthesis to occur

It is very difficult to explain here. We are talking about electron 
transfer reactions. This means that it takes nanoseconds to occur. The hole 
process of transfer from the chlorophyl to the other molecules can happen 
thousands of times in a second. It is important to remember that there are 
other pigments involved (remember that not all leaves have the same colour) 
and some of them protect the photosystem from "burning" in the excess of 
light.
Since photosynthesis is a very important metabolic pathway in the plant, it 
interacts with almost every signal from the enviroment or from the other 
pathways. Nitrogen metabolism, for example, is closely related to carbon 
metabolism and this allow the plant to respond to changes in the soil 
conditions. Water is also very important. If the plant cannot absorb water 
from the soil, its stomata will close and the leaves will not be able to 
get CO2 from the atmosphere and, therefore, photosynthesis will stop. There 
are many strategies that the plant can use to get rid of the excess of 
light under these conditions, but that is another story.
Hope i answered you question. Bye.