Across
- 5. tiny organisms that are made of a single cell
- 6. a group of atoms joined together in a particular way
- 7. anything that has mass and takes up space
Down
- 1. water that is underground
- 2. a set of interacting parts forming a complex whole
- 3. heater a heating unit that stores and warms water
- 4. the moment when two objects hit each other