Cellular Respiration & Photosynthesis?

Question

In what ways are the process of photosynthesis and cellular respiration dependant upon eachother?

Answer 1

Respiration and photosynthesis are certainly complementary in function and do interact.  Respiration is entirely dependent on carbohydrates as a source of energy and carbon.  These carbohydrates come totally from photosynthesis.  It should be also mentioned that there is a special form of respiration called "photorespiration" that all plants exhibit to varying degrees.  This process specifically uses a 2-carbon compound called glycolic acid which is an early product of photosynthesis as a substrate.  Thus, this respiratory process is special because it only occurs in the light and actually acts to oppose the net uptake of CO2 from the atmosphere which is characteristic of photosynthesis.  Clearly, photorespiration is a process where photosynthesis and respiration interact greatly and closely.

It is less studied but there is good reason to believe that photosynthesis interacts directly with respiration in the chloroplast using metabolic processes quite distinct from photorespiration.  The benefit appears to be that in very low light or darkness the respiratory process keeps electron carriers involved in photosynthesis in a proper state of oxidation.  This could facilitate optimal performance of the system in very low light.