Explain the following terms:
Photolysis
Topic: Photolysis
Answer
PHOTOLYSIS is the SPLITTING OF WATER molecules into hydrogen ions and oxygen, in the presence of sunlight and chlorophyll, during the LIGHT REACTION of photosynthesis.
The word defines itself: PHOTO (light) + LYSIS (splitting).
WHY IT MATTERS: photolysis supplies the HYDROGEN that is picked up by NADP and carried into the dark reaction to reduce carbon dioxide into glucose. The OXYGEN released is a by-product — and it is the source of all the free oxygen in the earth’s atmosphere.
IT ALSO SETTLES A COMMON MISCONCEPTION: the oxygen given off in photosynthesis comes from WATER, not from carbon dioxide. That was proved using radioactive oxygen-18 as a tracer.
Do not confuse it with PHOTOPHOSPHORYLATION, the other light-reaction event, which converts ADP into ATP. Read the second half of the word.