Science

2. A nonliving physical or chemical part of an ecosystem.
6. The continuous movement of carbon through Earth, its atmosphere, and the living things on Earth.
9. All the living and nonliving things that interact in a particular environment.
10. A region of Earth that has a particular climate and certain types of plants.
11. A series of events or actions that repeat themselves regularly.
12. A term used to describe cone-bearing trees and shrubs that usually keep their leaves or needles during all the seasons of the year.
14. A model used to show a relationship between a single producer and a chain of consumers in an ecosystem.
16. The lower end of a river where it meets the ocean and fresh and salt waters mix.
18. The continuous movement of nitrogen through Earth, its atmosphere, and the living things on Earth.
19. A term used to describe trees and shrubs that drop their leaves when winter comes.
20. A group of organs that provides protection against disease-causing agents.

1. A protein produced by some white blood cells to attack specific foreign materials.
3. A natural process that involves a gradual change in the plant and animal communities that live in an area.
4. The continuous movement of water through Earth, its atmosphere, and the living things on Earth.
5. The structures in the body that work together to transform the energy and materials in food into forms the body can use.
7. A blood vessel with strong walls that carries blood away from the heart.
8. An interaction between two species in which one species benefits without harming the other; a type of symbiosis.
13. The scientific study of how living things interact with each other and their environment.
15. Resistance to a disease.
17. A type of blood cell that picks up oxygen in the lungs and delivers it to cells throughout the body.