Across
- 2. thin layer of gases that surrounds Earth
- 5. the study of interactions among organisms and their environment
- 9. a nonliving factor that shapes an ecosystem
- 11. different populations living together in an area
- 12. pure substance made up entirely of one type of atom
- 13. layer of permanently frozen subsoil
- 16. protein catalyst that speeds up the rate of a reaction
Down
- 1. positively charged particle
- 3. change over time
- 4. fats, oils, and waxes are examples of this macromolecule
- 6. all of the rock at and below Earth's surface
- 7. first step in scientific method
- 8. a statement that can be tested with an experiment
- 10. substance that speeds up the rate of a reaction
- 14. the basic unit of matter that is nonliving
- 15. the smallest unit of an organism that is living