The Living Environment The study of organisms and their interactions with the environment. Topics Unit 1: Ecology Unit 2: The Cell Unit 3: Genetics Unit 4: History of Biological Diversity Unit 5: The Human Body The Human Body Homeostasis and the Human Body Integumentary, Skeletal, and Muscular Systems Nervous System and Endocrine Systems Circulatory and Respiratory Systems Digestive and Excretory Systems Human Reproduction and Development The Immune System Homeostasis and The Human Body All living organisms display levels of organization, and each level is necessary to maintain homeostasis. Atom Molecule Macromolecule Organelle Cell Tissue Organ Organ System Organism Homeostasis and The Human Body