Which gas makes up 78 percent of our atmosphere? It can be used by plants only when transformed by bacteria or lightning. oxygen
nitrogen
hydrogen
carbon

Which describes a difference between cephalopods and gastropods? cephalopods have a water vascular system, and gastropods have an open circulatory system. cephalopods live only in ocean environments, and gastropods live in a variety of environments. cephalopods have a simple nervous system, and gastropods have a complex nervous system. cephalopods are the largest group of mollusks, and gastropods are the smallest group of mollusks.