Our atmosphere is _____% nitrogen gas

Plants use CO₂ in the process of _____ to make _____ and O₂

A(n) _____ is fresh (drinking) water underground

Animals use O₂ in the process of _____ to make more CO₂

Higher organisms use nitrogen to make their

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

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

Human processes mainly contribute to the

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

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

_____ are the main regulators of CO₂ in the atmosphere because CO₂ dissolves easily in them.

Another natural source for CO₂ is _____.

During _____, water evaporates directly from glacial ice.

The water cycle is driven by

_____ is when water evaporates from plants and goes into the atmosphere.

_____ occurs when water droplets that are large enough fall from clouds.

Water vapor that collects into a liquid is called _____.

Describing the cycling of elements between living organisms and the non-living environment.

Process of describing how water seeps through the soil into groundwater

Which biogeochemical cycle does NOT include a major path in which the substance cycles through the atmosphere?

Lightning, legumes, and bacteria are all part of which cycle?

Which of the following is NOT a way that carbon in dead organisms is returned to the carbon cycle?

In the water cycle, at which point does water enter?

Scientists estimate that it can take a single water molecule as long as _____ years to complete one cycle.