Well the way one living thing depends on another living thing would be like an example from the food chain. Grass is grown from the ground as we all know, then something like an herbivore; like a rabbit, would come along and eat the grass. Then comes along the carnivore, like a fox, may come along and eat the rabbit. The fox depends on the rabbits to eat that way he can survive. When the fox dies, he decomposes and becomes nutrients for the grass to grow, and the cycle continues. :) hope this helps