The fourth thing plants need is water. Good ol' H2O is critical for a plant to make and move nutrients from the roots to the leaves and back again. Not enough water, or too much of it and a plant will die. Number five is air. Plants can use carbon dioxide in the air and give us oxygen in return.
Dirty air can hurt plants, in fact pollution can do deadly damage.
Finally, just like humans, plants need nutrients. The most important being nitrogen, phosphorus and potassium. Nitrogen gives plants their dark green color. Phosphorus helps with flower and seed production and the development of a strong root system. Potassium helps fight off disease and encourage strong stem growth.