Microfiltration Water under pressure passes into pipes constructed of filter membranes with tiny pores too small to admit suspended solids and some pathogens. In most cases this means that water has to be piped from many kilometres away. 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.