Across
1
Group of similar cells
2
Center of an atom or cell
5
Biological catalyst
6
Form of thermal energy
7
Unit of heredity
10
Measure of matter in an object
11
Substance with pH below 7
12
The Red Planet
Down
2
Nerve cell in the brain
3
Glass that splits light into spectrum
4
Blocking of light by a celestial body
8
Second lightest element
9
Icy body with a tail near the sun