Cells, tree, digestive system, public transportation system, government systems, school systems, families, dog, forest, pond, prairie, communication systems, towns, insect, solar system, weather systems, bird, correctional system, squirrel, soil, etc.
Simple species that can tolerate the often- harsh environment become established first. These organisms help enrich the soil, allowing other species to become established. The first organisms to appear in areas of primary succession are often mosses or lichens.
Atoms bound together and form molecules. Molecules are a little more complex than atoms. For example water is composed of two hydrogen atoms and one oxygen atom which are both gases. Properties of oxygen and hydrogen are completely different than water molecules.
