Across
1
Ball of burning gas in space
4
Center of an atom or cell
5
Biological catalyst
8
Unit of electric potential
Down
2
Element found in all living things
3
Substance with pH above 7
6
Gas essential for breathing
7
Blocking of light by a celestial body
9
Tissue that contracts for movement
10
Measure of matter in an object
11
Natural satellite of Earth