The carbon in coal, oil, and natural gas came from

• the combustion of fossil fuels.

• the remains of dead organisms.

• carbon-fixing bacteria in swamp soil.

• carbon dioxide dissolved in ocean water.

How does most of the carbon in an organism’s body return to the environment after the organism dies?

• Decomposers break the body down into simpler compounds.

• Heat from the sun causes the carbon in the body to evaporate.

• Geological processes cause the body to turn into a fossil fuel.

• Rainwater dissolves the carbon in the body and carries it to the ocean.

Human processes mainly contribute to the

• release of carbon dioxide into the atmosphere.

• decrease of the total amount of carbon found on Earth.

• depletion of carbon dioxide reserves in the atmosphere.

• increase in the amount of carbon contained in rock materials.

Nitrogen, in the form of ammonia, nitrate, and nitrite, is found in the soil.

• True

• False

Nitrogen fixation is the process in which certain bacteria convert nitrogen gas into nitrates.

• True

• False

Denitrification is the process by which some soil bacteria convert nitrates into nitrogen gas.

• True

• False

All organisms require nitrogen to make amino acids, which in turn are used to build carbohydrates.

• True

• False

Phosphate is released as rocks and sediments wear down.

• True

• False

Plants absorb phosphate from the soil or from water

• True

• False

Phosphorus is the most abundant gas in the atmosphere.

• True

• False