Carbon Cycle

What are the two major components of the carbon cycle?

The conversion of CO2 into organic carbon (reduction) and the return of organic carbon to CO2 through mineralization (oxidation).

Why is carbon considered the fundamental building block of life?

Carbon forms the backbone of organic molecules that make up all living organisms and participates in essential biochemical processes.

In what forms does carbon primarily exist in the atmosphere?

Carbon exists mainly as carbon dioxide (CO2) and also as methane (CH4), a potent greenhouse gas.

What are oxidized vs. reduced forms of carbon?

Oxidized carbon (e.g., CO2) is a good electron acceptor, while reduced carbon (e.g., CH4) is a good electron donor.

What are the three main forms in which carbon circulates in nature?

Carbon circulates as CO2, methane (CH4), and organic carbon compounds.

What is the definition of the carbon cycle?

The carbon cycle is the movement of carbon through the environment, organisms, and atmosphere via biological, chemical, and physical processes.

What is autotrophy in the carbon cycle?

Autotrophy is the process of converting CO2 into organic carbon using energy from light or chemicals.

What is heterotrophy in the carbon cycle?

Heterotrophy is the consumption of organic carbon and its conversion back to CO2 through respiration.

What are primary producers in the carbon cycle?

Primary producers are autotrophs (e.g., plants, algae, cyanobacteria) that fix CO2 into organic matter.

What enzyme is responsible for most CO2 fixation?

Rubisco, encoded by the rbcL gene, catalyzes CO2 fixation during photosynthesis.

What are photoautotrophs?

Photoautotrophs are organisms that use sunlight to convert CO2 into organic matter (e.g., plants, algae, cyanobacteria).

What are chemoautotrophs?

Chemoautotrophs are organisms that use chemical energy (not light) to fix CO2 (e.g., nitrifiers, sulfur oxidizers).

What role do heterotrophs play in the carbon cycle?

Heterotrophs consume organic carbon and release CO2 through respiration.

What are decomposers in the carbon cycle?

Decomposers are organisms (mainly microbes) that break down organic matter, returning carbon to the environment.

What is mineralization in the carbon cycle?

Mineralization is the microbial conversion of organic carbon back into CO2.

What processes restore CO2 to the atmosphere?

Respiration, combustion (burning), and microbial decomposition release CO2 into the atmosphere.

What is cellulose and why is it important in decomposition?

Cellulose is the most abundant plant polymer and is rapidly decomposed by microbes.

Which organisms decompose cellulose?

Fungi (e.g., Aspergillus, Trichoderma) and bacteria (e.g., Clostridium, Bacillus) degrade cellulose.

What is hemicellulose?

Hemicellulose is a plant polymer made of various sugars that is decomposed by microbial enzymes called hemicellulases.

Why is lignin decomposition slow?

Lignin is a complex and resistant plant polymer that is difficult for microbes to break down.

What organisms degrade lignin?

Certain fungi (e.g., Aspergillus) and bacteria (e.g., Streptomyces) can degrade lignin slowly.

What is a carbon pool?

A carbon pool is a reservoir where carbon is stored, such as soils, oceans, atmosphere, and fossil fuels.

What is a carbon flux?

A carbon flux is the rate at which carbon moves between reservoirs over time.

What are major carbon sources?

Carbon sources release CO2, including fossil fuel burning, deforestation, and respiration.

What are major carbon sinks?

Carbon sinks absorb more CO2 than they release, including forests, oceans, and soils.

Why are forests considered carbon sinks?

Forests absorb CO2 through photosynthesis and store it in biomass and soil.

What is the fast carbon cycle?

The fast carbon cycle involves rapid CO2 exchange between atmosphere and organisms over days to decades.

What is the slow carbon cycle?

The slow carbon cycle involves carbon stored in rocks and fossil fuels over thousands to millions of years.

What causes increased atmospheric CO2?

Burning fossil fuels and land-use changes increase CO2 levels in the atmosphere.

What is methane (CH4) and why is it important?

Methane is a potent greenhouse gas produced by microbes and contributes to climate change.

What is methanogenesis?

Methanogenesis is the anaerobic microbial production of methane by archaea.

Which organisms perform methanogenesis?

Methanogenesis is carried out by methanogens, which are archaea (Euryarchaea).

What are the main substrates for methanogenesis?

CO2 + H2 and acetate are used by methanogens to produce methane.

Why is methanogenesis oxygen-sensitive?

Methanogens require anaerobic conditions because oxygen inhibits their metabolism.

What is methane oxidation?

Methane oxidation is the conversion of CH4 into CO2 by aerobic bacteria called methanotrophs.

Where do methanotrophs live?

Methanotrophs live in oxygen-rich zones above methanogenic environments or in upland soils.

What is carbon sequestration?

Carbon sequestration is the long-term storage of carbon in oceans, soils, or vegetation to reduce atmospheric CO2.

What are the three steps of carbon sequestration?

Capture of CO2, transport to storage site, and long-term storage away from the atmosphere.

What is geological carbon sequestration?

The storage of CO2 underground in rock formations to prevent atmospheric release.

What is ocean carbon sequestration?

The storage of CO2 in deep ocean waters via natural or artificial processes.

What is terrestrial carbon sequestration?

The storage of carbon in plants and soils through photosynthesis.

How do microbes contribute to carbon sequestration?

Microbes store carbon through decomposition, CO2 conversion, carbonate formation, and soil aggregation.

What is carbonate induction?

Some microbes promote the formation of carbonates, which trap and store carbon.

How do microbes form soil aggregates?

Microbes produce sticky substances that bind soil particles, protecting carbon from decomposition.

What role do mycorrhizal fungi play in carbon storage?

They exchange nutrients with plants and increase carbon storage in soils.

What is the relationship between photosynthesis and respiration in the carbon cycle?

Photosynthesis removes CO2 from the atmosphere, while respiration returns it, maintaining balance.

How do anthropogenic activities impact the carbon cycle?

Human activities increase CO2 emissions, disrupting natural carbon balance and driving climate change.

What is the biological pump in the ocean?

The process by which marine organisms transport carbon from surface waters to deep ocean storage.

Why is carbon cycling important for ecosystems?

It regulates climate, supports life, and maintains energy flow through food webs.