Across
1
Fourth state of matter
4
Unit of heredity
6
Molten rock beneath Earth surface
7
Group of similar cells
9
Gas essential for breathing
11
Substance with pH above 7
Down
2
Center of an atom or cell
3
Blocking of light by a celestial body
5
Smallest unit of an element
8
Ball of burning gas in space
10
Particle of light
12
Substance with pH below 7
13
Positive particle in nucleus