Across
1
Gas essential for breathing
5
Precious yellow metallic element
6
Preserved remains of ancient life
7
Tissue that contracts for movement
8
Unit of electric potential
11
Unit of heredity
12
Naturally occurring inorganic solid
Down
2
Smallest unit of an element
3
Blocking of light by a celestial body
4
Nerve cell in the brain
9
Icy body with a tail near the sun
10
Second lightest element