Photosynthesis is important because it's the process of which a plant makes its own food using light (as well as providing oxygen for the earth). Without it, the earth would most likely die, and we would with it.
Cellular respiration relies on photosynthesis to make food(sugar) so that cellular respiration can happen. Cellular respiration is important because it's the process of releasing the chemical energy stored in the food it makes.
Fermentation breaks down chemicals to provide energy. This is usually a substitute process for a plant, if it does not have enough oxygen to perform cellular respiration. Fermentation is another method for producing energy.
