Across
1
Biological catalyst
3
Path of a planet around the sun
7
Unit of force
8
Positive particle in nucleus
9
Ball of burning gas in space
11
Molten rock beneath Earth surface
12
Center of an atom or cell
Down
2
Substance with pH above 7
4
Hottest planet in solar system
5
Nerve cell in the brain
6
Unit of energy
10
Smallest unit of an element