The processes of photosynthesis and chemosynthesis both provide energy for ecosystems. Photosynthesis is the process that plants use to supply energy to their ecosystems. Photosynthesis uses sunlight, carbon dioxide, and water to create glucose (sugar, energy) and gives off oxygen as a byproduct. The process of chemosynthesis is similar in that it also creates energy for an ecosystem. However, chemosynthesis is done in the absence of sunlight. Bacteria perform the process of chemosynthesis by using chemicals (like sulfur compounds), carbon dioxide, and water to create energy. Another difference between photosynthesis and chemosynthesis is that chemosynthesis does not give off oxygen as a byproduct, like photosynthesis does.