Photosynthesis is an example of a biochemical pathway. Let's look at the term to dissect it. "Bio" clearly comes from biological, meaning related to a biological system (in this case plants). "Chemical" means that photosynthesis is a collection of chemical reactions. "Pathway" means that it is a series of reactions that lead from an initial set of reactants to a final set of products through numerous steps and intermediates. Ultimately, photosynthesis takes carbon dioxide and water and produces glucose (a sugar) and oxygen. But this doesn't just happen in one step. It occurs over a series of tens of reactions (possible over one hundred reactions) where electrons are shuffled through a series of chemical intermediates to make the ultimate products.