Photosynthesis and Cellular respiration - help!

[RazzMeTazz]

Hi guys 

I had a few questions about certain parts of photosynthesis and cellular respiration and any help would be appreciated!

1.) Is the light-dependent reaction an exergonic reaction, overall?
2.) Is the light-independent reaction an endergonic reaction, overall?
3.) When the light intensity increases, the rate of photosynthesis also increases but eventually the rate of photosynthesis no longer increases and plateaus. Why is this so?
4.) Are the carbons which are cleaved off the pyruvate molecules, during the link reaction attached to O2 so that they can be released as C02? Does that mean O2 is an input in the link reaction?
5.) Why would the Kreb's cycle shut down, if there was no oxygen present?


Thanks!