How much oxygen is contained in the atmosphere?
a. 20%
b. 21%
c. 22%
d. 23%

what is slowed when water is a limiting factor in an environment?
a. amount of evaporation
b. population growth
c. the types of rocks

Oxygen makes up 20% of the atmosphere while nitrogen makes up 78%. The other two percent is made up of other gases. Population growth would slow. Organisms need water to survive and if there is a limited amount of water, populations will decline. 

There is sand and mud