Why do organisms have a common name and a scientific name?

The reason that organisms have common and scientific names is because there has to be a universal name for all organisms in theory.

Common names can be many different things, dependent on the area of the world you live in,  Scientific Names are part of a series called binomial nomenclature which is a universal way to name all organisms.  For example, a goose will be called anser anser across the world, then it changes some when you go into breeds, but for the most part, you can get by with that name.  

a. the production of carbon dioxide through the process of photosynthesis