Photosynthesis is the process by which plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose (sugar), releasing oxygen as a byproduct, essentially transforming light energy into chemical energy that can be stored as food for the organism; it's a crucial process for life on Earth as it provides the oxygen we breathe and the foundation of the food 

Cellular respiration is the biological process where cells break down glucose (sugar) in the presence of oxygen to release energy in the form of ATP (adenosine triphosphate), which can be used by the cell to perform various functions, while also producing carbon dioxide and water as waste products; essentially, it's how cells "breathe" to generate energy from food.