Chapter 6

3. a cell that collects excess water in a flatworm
5. a heart chamber that receives blood returning to the heart
7. an organ of excretion found in vertebrates
11. the largest part of the brain that controls thought, memory, and body movement
13. an animal that eats plants
14. a substance that speeds up chemical changes
16. an animal that eats other animals
18. a way of getting food by straining it out of the water

1. the part of the digestive tract of some animals that grinds food
2. a chemical signal that a nerve cell releases
4. the movement of materials from an area of high concentration to an area of low concentration
6. get rid of wastes or substances that are not needed
8. a message that travels along nerve cells
9. a chemical signal that glands produce
10. form and release, or give off
12. a heart chamber that pumps blood out of the heart
15. a bunch of nerve cells that are loosely connected
17. take in oxygen and give off carbon dioxide