Across
1
Particle of light
3
Substance with pH below 7
5
Group of similar cells
6
Unit of electric potential
7
Measure of matter in an object
10
Blocking of light by a celestial body
11
Mass per unit volume
12
Basic unit of life
Down
2
Center of an atom or cell
4
Preserved remains of ancient life
8
Absolute temperature scale unit
9
Gas essential for breathing
13
Unit of energy