Biogeochemical Cycles

What is the main reservoir of carbon?

The atmosphere and oceans.

How do plants obtain carbon?

Plants absorb carbon dioxide (CO₂) from the atmosphere during photosynthesis.

How do animals obtain carbon?

Animals get carbon by eating plants or other animals.

What processes return carbon to the atmosphere?

Respiration, decomposition, and combustion.

Why is the carbon cycle important?

It recycles carbon, supports life, and helps regulate Earth’s climate.

What is the largest reservoir of nitrogen?

The atmosphere.

Why can’t most organisms use atmospheric nitrogen directly?

Atmospheric nitrogen (N₂) must first be converted into usable forms by bacteria.

What is nitrogen fixation?

The process in which bacteria convert atmospheric nitrogen into ammonia or other usable nitrogen compounds.

How do plants obtain nitrogen?

Plants absorb nitrates from the soil through their roots.

How do animals obtain nitrogen?

Animals get nitrogen by eating plants or other animals.

What is nitrification?

The process in which bacteria convert ammonia into nitrites and then nitrates.

What is denitrification?

The process in which bacteria convert nitrates back into nitrogen gas, returning it to the atmosphere.

Why is the nitrogen cycle important?

Nitrogen is needed to make proteins and DNA.

What is the main reservoir of phosphorus?

Rocks and soil.

How is phosphorus released into the environment?

Weathering of rocks releases phosphate into the soil and water.

How do plants obtain phosphorus?

Plants absorb phosphate from the soil.

How do animals obtain phosphorus?

Animals get phosphorus by eating plants or other animals.

How is phosphorus returned to the soil?

Decomposition returns phosphorus to the soil.

Does the phosphorus cycle have an atmospheric phase?

No. The phosphorus cycle has no significant atmospheric phase.

Why is phosphorus important?

It is needed to make DNA, RNA, ATP, bones, and teeth.

What is the sulfur cycle?

The sulfur cycle is the movement of sulfur through rocks, soil, water, the atmosphere, plants, animals, and microorganisms.

What is the main reservoir of sulfur?

Rocks and minerals.

How is sulfur released into the environment?

Weathering of rocks releases sulfate into the soil and water.

How do plants obtain sulfur?

Plants absorb sulfate from the soil.

How do animals obtain sulfur?

Animals get sulfur by eating plants or other animals.

How is sulfur returned to the soil?

Decomposition of plants and animals returns sulfur to the soil.

What role do bacteria play in the sulfur cycle?

They convert sulfur compounds into different forms, such as sulfate and hydrogen sulfide.

How does sulfur enter the atmosphere?

Volcanic eruptions, sea spray, and burning fossil fuels release sulfur dioxide (SO₂).

Why is the sulfur cycle important?

Sulfur is needed to make certain amino acids, proteins, and vitamins, and it helps maintain healthy ecosystems.

Which biogeochemical cycle has no significant atmospheric phase?

The phosphorus cycle.

Which cycles include an atmospheric phase?

The carbon, nitrogen, and sulfur cycles.

Which cycle is most closely associated with photosynthesis?

The carbon cycle.

Which cycle depends on nitrogen-fixing bacteria?

The nitrogen cycle.

Which cycle begins with the weathering of phosphate-rich rocks?

The phosphorus cycle.

Which cycle involves sulfur dioxide (SO₂)?

The sulfur cycle