Photosynthesis occurs in plants and produces glucose and oxygen (O2). The reactants needed are Water, Carbon Dioxide, and Light energy. Animals and humans need the glucose to eat (like apples) and need the oxygen to breathe.
The Carbon Dioxide enters through the stomata in the leaves (tiny holes in the leaf). The water is absorbed from the root system and goes up through the xylem to get to the leaves. Light energy helps the chloroplast break down the carbon dioxide. As a result, glucose and oxygen are made!
Cellular respiration occurs in plants and animals. During cellular respiration, carbon dioxide (CO2) is given off by the animal/plant. This carbon dioxide is then taken in by the plants and the cycle repeats. Cellular respiration occurs during day and night while photosynthesis just occurs during the day.