Leaching of compounds from mine tailings often results in the oxidation of two elements: _____ and _____ .

Nitrogen exists primarily as _____ in the environment.

Most chemical elements exist in the environment as _____.

a. usable forms in soil and rock

b. usable forms in water

c. unusable forms in soil and rock

d. unusable forms in water

Organisms typically make use of phosphorus in the form of _____.

In the carbon cycle, microbes convert _____.

a. CO₂ into organic material for consumption

b. CO₂ into inorganic material for storage

c. fossil fuels into usable organic compounds

d. oxygen into water as a by-product of photosynthesis

_____ Plants and bacteria start the carbon cycle with consumption.

Carbon fixation is the conversion of _____ into organic compounds.