why do plants and animals depend on each other

The plants take in carbon dioxide from the surroundings and water vapour also for the process of photosynthesis which gives them food . after photosynthesis they give out oxygen and carbohydrates . We human beings and animals inhale this oxygen and give out carbon - dioxide which is again used by the plants for thier food . If plants are not there we will not have enough oxygen to live and plants need animals because the dead and decaying matter provides them nutrients and humans also take care of plants so plants and animals are dependent on each other.