Explanations that have been repeatedly tested and not disproven are tentatively accepted. The principles of biology can be applied to world problems such as overpopulation, disease, environmental degradation, famine, and drug addiction. Each structure or activity is in a specific relationship to all other structures and activities. Organized chemical steps break down and build up molecules, making energy available or building needed parts. Using their own power, organisms move themselves or their body parts.
Organisms perceive the environment and react to it.
Organisms give rise to others of the same type. Ordered sequences of progressive changes result in increased complexity. Organisms have units of inheritance called genes that are passed from parent to offspring and control physical, chemical, and behavioral traits. Through evolution, species acquire new ways to survive, to obtain and use energy, and to reproduce. Specific structures and behaviors suit life forms to their own environment.