Invisible and Invaluable

8. Base that pairs with thymine or uracil
9. Product of an experiment
10. Disease-causing microbe, for example
11. Virus that causes a vaccine-preventable childhood disease
12. By its very nature: 2 wds.
14. Used to be
16. Organ that regulates equilibrium
18. Descriptor for a relationship in which an organism benefits without harming its host
21. Created a mathematical simulation
22. Organ that regulates pain
23. Earth's outermost layer
24. Sugar present in the milk of many mammals

1. Organism that benefits at the expense of its host
2. Precious gemstones
3. Gap between tectonic plates
4. Standard of measurement
5. Organism that derives mutual benefit from a relationship
6. Color imparted by some carotenoids
7. Hypothesis or conclusion
13. The Arecibo Observatory, for example
15. Tiny fragment of wood
17. Bone that parallels the ulna
19. Part of a biological network
20. Phenomenon caused by blockage of light by an object
21. Some in vivo test subjects
22. Dorsum