Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number.

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Across: 4. A system of arranging like things in groups. 6. A structure or behavior that enables a plant or animal to live successfully in its environment. 8. A plant-eater; an animal that only eats plants. 11. The coloring or characteristics of a plant or animal used to disguise or to conceal itself from an enemy. 12. The level or depth in the ground where the rock is completely filled with water and there are no air spaces (two words). 16. An animal that seizes and kills another animal for food. 17. An odorless, colorless gas formed by living or decaying plants and animals; the bubbles in soft drinks (carbon dioxide chemical formula). 18. To disappear into a liquid. 19. A plant or animal that occurs in a region naturally. 21. An animal that is seized by a predator. 22. A set or arrangement of things so related as to form a whole. 23. The study of the interrelationships between living things and the relationships between organisms and their physical environment. 24. The place where a plant or animal lives.

Down: 1. A living community of plants an animals and the physical environment (air, water, sunlight, soil) around them. 2. A meat-eater; an animal that only eats animals. 3. Surroundings; all of the conditions surrounding and affecting the development of an organism. 5. No longer in existence. 7. A compound capable of dissolving limestone. 9. An especially suitable place to live. 10. An animal that eats both plants and animals. 13. Foreign, introduced into an area where it does not naturally occur. 14. A speleothem or cave decoration which is a fragile, honeycomb-shaped structure of calcite attached to the walls and ceilings of a cave. 15. To protect from harm or danger; a place where animals and plants are kept for protection. 20. To cause; to come into being; anything brought about by a cause.