green plants perform photosynthesis to provide food for themselves & food is a source of energy for plants ->  green plants perform photosynthesis to provide energy for themselves  a source of something produces that something & photosynthesis is a source of energy for the plant by converting carbon dioxide, water, and sunlight into carbohydrates ->  photosynthesis produces energy by converting carbon dioxide, water, and sunlight into carbohydrates  photosynthesis is a kind of chemical process & if a process produces a thing by converting something into something else then that process produces that thing from that something ->  if photosynthesis produces a thing by converting something into something else then that photosynthesis produces that thing from that something  photosynthesis produces energy by converting carbon dioxide, water, and sunlight into carbohydrates & if photosynthesis produces a thing by converting something into something else then that photosynthesis produces that thing from that something ->  photosynthesis produces energy from sunlight  green plants perform photosynthesis to provide energy for themselves & photosynthesis produces energy from sunlight ->  green plants produce energy from sunlight  green plants produce energy from sunlight & grass is a kind of green plant -> grass produces energy from sunlight