Organisms must have energy to carry out essential life functions, like moving, reproducing or even breathing. Some organisms, called heterotrophs, must obtain their energy from food by breaking it down into macromolecules then glucose. Autotrophs make their own food (glucose and other simple sugars). All living things turn glucose and other simple sugars into ATP (adenosine triphosphate). ATP is like the energy currency for organisms, it is accepted in every type of cell at any time. Organisms use ATP as energy for life functions (breathing, growing, etc). In this unit, you will explore how food is created from sunlight, carbon dioxide, and water in autotrophs, called photosynthesis and how food is broken down into ATP in hetertrophs and autotrophs, called cellular respiration (yes, it involves breathing!).