If plants no longer exsisted on earth, we would be dead. We need plants to survive, they are our main source of oxygen and withought oxygen, humans die. But lets say that we didn't need oxygen to survive, just food. If we dont have plants we wouldnt have nutrients and our animals wouldnt have food. No plants, no food for cows or chickens to eat. Withought animals like that predators would also be starved because they have no food. So we have no food. So in conclusion, WE NEED PLANTS!!