Photosynthesis – The cycle of plants and how they make energy! The sun(light energy), water, minerals and carbon dioxide are all absorbed by the plant. The plant then uses them to make glucose/sugar, which is the energy/food for the plant. Oxygen is also produced by the plant in this cycle, which is then let off into the air! Have you noticed how clean and pure the air feels when there are plants around? They are filling the air with oxygen!