1. the high energy chemical compound with three phosphate groups that provides energy for all other cell activities endocytosis 2. chemical reactions in plants and animals that break down food molecules into energy (atp) adenosine triphosphate (atp) 3. movement of particles or molecules from higher concentration to lower concentration homeostasis 4. when cells engulf or ingest substances diffusion 5. when cells expel or get rid of substances from within cellular respiration 6. the relatively constant state in the internal environment of an organism exocytosis 7. a solution that has a higher salt concentration than the salt hypertonic