Photosynthesis vs. Cellular Respiration

Photosynthesis is the process of making glucose that will end up being used by all organisms on earth, and cellular respiration is the process of converting glucose into ATP. The chemical reaction of photosynthesis is 6H2O+ 6CO2 --[light and chlorophyll]--> C6H12O6 + 6O2 and the chemical reaction of cellular respiration is the reverse of that, only, it does not need light or chlorophyll to happen.

The two processes are similar in that they have the same substances in the beginning and end. As well, both processes are needed to ensure that cells in an organism get the ATP they need. In both processes, ATP is produced. In the light dependent reaction of photosynthesis, ATP is made during the chemiosmosis of hydrogen ions through ATP synthase. In glycolysis, Krebs cycle, and the electron transport chain of cellular respiration, ATP is produced. 

In glycolysis, ATP is produced when BPG is converted into PGA (two molecules of ATP are produced, as glycolysis yields two BPGs). In the Krebs cycle, ATP is made when succinyl CoA becomes succinate (again, two ATPs are made). Finally, in the ECT, ATP is made when electrons pass through NADH dehydrogenase, coenzyme Q and cytochrome b-c1 complex, and cytochrome oxidase complex (COC).

Both cellular respiration and photosynthesis need the proton gradient across membranes to power ATP synthase, which in turn, makes ATP. As protons move through ATP synthase, it attaches another phosphate unto ADP to make 3 phosphates.

Finally, both these processes happen inside organelles with double membranes. Photosynthesis happens in chloroplasts (in plants and bacteria), and cellular respiration happens in mitochondria (all other organisms). 

Photosynthesis and cellular respiration have many differences as well as similarities, but in the end, they are both very important processes living things need to obtain energy.