taking in carbon dioxide is a stage in the photosynthesis process & if something is a stage in a process then that something helps that process ->  taking in carbon dioxide helps the photosynthesis process  taking in carbon dioxide helps the photosynthesis process & carbon dioxide can be found in the air ->  taking in carbon dioxide from the air helps the photosynthesis process  taking in carbon dioxide from the air helps the photosynthesis process & photosynthesis is a source of / makes food / energy for the plant by converting carbon dioxide, water, and sunlight into carbohydrates -> taking in carbon dioxide helps a plant make food