Pipes are expensive to build so water becomes more expensive as a city grows. The trees are the obvious ones. Mammals and birds live in the trees. Ants collect the seeds. Mosses and fungi live on the forest floor.
Lizards eat the ants or the fungi.
Millions of microbes live in the soil. Parasites Some animals and plants are parasites. We may need to add a substance such as chlorine that kills any living organisms whether they are parasitic or not. Pathogens Any organism that causes disease in another is described as pathogenic. People People leave things behind.