Puzzle 7

4. water that has been used and now contains harmful substances
5. the stuff that things are made of
7. a scientist who studies ecosystems
9. to try something again using what you learned the last time you tried it
11. a process in which substances change into different substances
16. what you can observe or measure about something that helps you figure out what it is
18. a group of atoms joined together in a particular way
19. water in the form of invisible gas
20. the process of returning something to its original condition by fixing or repairing it
21. matter that is made of only one kind of atom or molecule
22. able to dissolve in water or another liquid
23. an organism that breaks down droppings or dead organisms
24. a diagram that shows what eats what in an ecosystem

1. matter that is made of more than one substance
2. a supply of something that is useful
3. the air that surrounds Earth
6. a mixture of rocks, water, air, parts of dead organisms, and tiny living organisms
8. all the living things on Earth
10. the solid part of Earth
12. when a liquid turns into a gas
13. something taken in by plants and animals that helps them grow
14. when a gas turns into a liquid
15. a community of organisms together with its environment
17. all of the liquid water and ice on Earth