if a process converts something into something else then that something is used in that process & photosynthesis makes food for the plant by converting carbon dioxide, water, and sunlight into carbohydrates ->  photosynthesis uses carbon dioxide to make food for a plant  photosynthesis uses carbon dioxide to make food for a plant & carbon dioxide can be found in the air ->  photosynthesis uses carbon dioxide from the air to make food for a plant  photosynthesis uses carbon dioxide from the air to make food for a plant & carbon dioxide contains carbon ->  photosynthesis uses carbon from the air to make food for a plant  photosynthesis uses carbon from the air to make food for a plant & photosynthesis is a kind of chemical process -> photosynthesis is a kind of process that uses carbon in the air to make food for plants