Figure 4.8: The chloroplast is the photosynthesis factory of the plant. ( 7 )Oxygen: An Essential Byproduct
Oxygen is a byproduct of the process of photosynthesis and is released to the atmosphere
through the stomata. Therefore, plants and other photosynthetic organisms play an impor-
tant ecological role in converting carbon dioxide into oxygen. As you know, animals need
oxygen to carry out the energy-producing reactions of their cells. Without photosynthetic
organisms, many other organisms would not have enough oxygen in the atmosphere to sur-
vive. Oxygen is also used as a reactant in cellular respiration, which is discussed in the next
lesson, so essentially, oxygen cycles through the processes of photosynthesis and cellular
respiration.
The Light Reactions and the Calvin Cycle
The overall process of photosynthesis does not happen in one step, however. The chemical
equation of photosynthesis shows the results of many chemical reactions. The chemical
reactionsthatmakeuptheprocessofphotosynthesiscanbedividedintotwogroups: thelight
reactions (also known as the light-dependent reactions, because these reactions only occur
during daylight hours) and the Calvin Cycle, or the light-independent reactions. During the
light reactions, the energy of sunlight is captured, while during theCalvin Cycle, carbon
dioxide is converted into glucose, which is a type of sugar. This is summarized inFigure
4.9.