Across
1
Natural satellite of Earth
4
Positive particle in nucleus
6
Unit of heredity
8
Substance with pH below 7
9
Blocking of light by a celestial body
Down
2
Biological catalyst
3
Nerve cell in the brain
5
Gas essential for breathing
6
Force that attracts objects together
7
Reddish electrical conductor
10
Amplified beam of light
11
Tissue that contracts for movement