Across
1
Biological catalyst
5
Our home planet
6
Substance with pH below 7
7
Second lightest element
8
Hottest planet in solar system
9
Smallest unit of an element
11
The Red Planet
12
Gas essential for breathing
Down
2
Group of similar cells
3
Icy body with a tail near the sun
4
Center of an atom or cell
10
Unit of force