The Earth has a large collection of widely diverse environments in which living things manage to grow and survive. There are different approaches to photosynthesis that are more suitable than the standard approach in these different environments.
Some organisms forgo the use of light for energy production entirely.
However, all of these adaptations are variations on the same basic pathways of photosynthesis and respiration. In understanding these variations, you will better understand the pathways themselves. As mentioned previously, Rubisco is the most abundant enzyme on Earth. It is inarguable that this is a very important enzyme to all life, but it is believed that Rubisco is so abundant because of its inefficiencies. Rubisco will sometimes recognize oxygen as a substrate instead of carbon dioxide.