Across
1
Unit of heredity
3
Particle of light
6
Path of a planet around the sun
7
Hottest planet in solar system
9
Center of an atom or cell
10
Gas essential for breathing
12
Blocking of light by a celestial body
Down
2
Group of similar cells
4
Reddish electrical conductor
5
Unit of force
6
Compound containing oxygen
8
Element found in all living things
11
Precious yellow metallic element