The study of how organisms interact with each other and their physical environment. The community living in an area and its physical environment. In a closed system, the element that initiates an action in response to a signal from a sensor . In human systems, a muscle or gland often serves as an effector. In males, a short duct that connects the vas deferens from each testis to the urethra .
Electrons circle the atom's nucleus in regions of space known as orbitals.
A molecule that forms part of the electron transport system that transfers electrons ejected by chlorophyll during photosynthesis . ATP is formed by this process. The attraction between atoms of opposite charge that holds the atoms together in ionic bonds . Lung disease characterized by shortness of breath, often associated with smoking. The process by which human bones form from cartilage.