Across
1
Icy body with a tail near the sun
4
Center of an atom or cell
6
Particle of light
9
Hottest planet in solar system
Down
2
Compound containing oxygen
3
Curved glass that refracts light
5
Gas essential for breathing
6
Glass that splits light into spectrum
7
Tissue that contracts for movement
8
Smallest unit of an element
9
Infectious microscopic agent