To make this diversity more comprehensible, biologists classify species into categories. Some biologists recognize another kingdom, a very primitive type of prokaryote that they call Archaebacteria . There is unity in the diversity of life forms at the lower levels of organization. Scientific method - the means to the end. Where the answers come from.
Science is the systematic observation of natural phenomena.
It begins with careful observation, and is followed by description and record keeping. Observations are generally accepted as credible if the observations are repeatable. A natural sequel to observation is the formulation of a satisfactory explanation of the phenomenon. While not all observations require explanation, a careful set of observations and experimentation lead to a hypothesis. Hypotheses are tested by further experimentation, and modified if appropriate.