1. acceleration an increase in rate of change
2. acid any substance that in water solution tastes sour, changes the color of certain
indicators, reacts with some metals to liberate hydrogen, reacts with bases to form
salts, and promotes certain chemical reactions
3. acid rain rainfall that is more acidic than normal because of air pollution
4. activation energy the energy that an atomic system must acquire before a process (such as an
emission or reaction) can occur
5. adaptation the process of adjusting or conforming to new conditions
,6. adequacy the quality of being able to meet a need satisfactorily
7. air mass a large body of air throughout which temperature and moisture content are
similar
8. alimentary canal digestive tube that extends from the mouth to the anus
9. alveolus tiny air sac in the lung
10. amplitude greatness of size or range; magnitude
,11. antibody a protein that produces an immune response
12. aorta the large artery carrying blood from the heart to the body
13. artery a blood vessel that carries blood away from the heart to the body
14. assess to evaluate
15. asteroid any of numerous small celestial bodies composed of rock and metal
, 16. atmosphere the envelope of gases surrounding the Earth or another planet
17. atom Basic unit of matter
18. atomic mass the property of an atom that causes it to have weight; protons + neutrons
19. atomic number quantity of protons in the nucleus or an atom of an element
20. atrium a chamber connected to other chambers or passageways (such as the heart)
21. base lowest support of a structure