Well plant cells have both chloroplasts and mitochondria, and what happens is photosynthesis happens in the chloroplast (they produce their own food to eat for energy (sugar/glucose). The outcome of photosynthesis is glucose and oxygen which then goes to the mitochondria (where the process of cellular respiration takes place) which takes in the glucose and oxygen and turns that into carbon dioxide, water, and ATP energy. Where the plant goes through the process of making the food first before going through the process of turning into energy, animals just have the mitochondria, so they consume foods for the sugars needed and the mitochondria do the same work they did in the plant, just minus the photosynthesis.