Biogeochemical Cycles: Carbon Cycle Flashcards

These vocabulary flashcards cover the storage, fluxes, biological processes, and chemical reactions involved in the Earth's carbon cycle as described in the BIO 2207 lecture notes.

Carbon Cycle

The biogeochemical cycle by which carbon is exchanged among the biosphere, lithosphere, hydrosphere, and atmosphere of Earth.

Major Sources of Carbon

The three primary sources include atmospheric $CO_2$, $CO_2$ dissolved in water bodies ($H_2CO_3$), and Methane ($CH_4$).

Atmospheric $CO_2$ Quantity

The atmosphere contains $700 \times 10^9$ metric tonnes of $CO_2$, with an average of about $6$ tonnes of carbon as $CO_2$ over each acre of Earth.

Hydrosphere $CO_2$ Quantity

Water bodies contain $35000 \times 10^9$ metric tonnes of $CO_2$.

Deep Ocean Carbon Storage

The deep ocean acts as a massive reservoir, storing $38,100$ Gigatonnes of Carbon ($GtC$).

Photosynthesis Reaction

Performed by plants, algae, and phytoplankton in the presence of light: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

Respiration Reaction

The process of utilizing biomolecules for cellular energy: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + E (ATP)$, which transfers carbon through successive trophic levels.

Aerobic Decomposition

The breakdown of complex organic matter by microbes and fungi in the presence of oxygen, releasing $CO_2$; example reaction: $(C_6H_{10}O_5) + nO_2 \rightarrow nH_2O + nCO_2 + C_{14}H_{12}O_8 + heat$.

Fulvic Acid ($C_{14}H_{12}O_8$)

A product formed, along with water and carbon dioxide, when cellulose is broken down during aerobic decomposition.

Hydrolysis (Anaerobic Decomposition Step 1)

The process where complex molecules like starch are broken down into constituent monomers like glucose: $(C_6H_{10}O_5) + nH_2O \rightarrow nC_6H_{12}O_6$, facilitated by Clostridium.

Acidogenesis (Anaerobic Decomposition Step 2)

The process where glucose is converted to alcohol, hydrogen, and carbon dioxide: $C_6H_{12}O_6 + 2H_2O \rightarrow 2CO_2 + 4H_2 + R-OH$, facilitated by Clostridium.

Acetogenesis (Anaerobic Decomposition Step 3)

The process where alcohol is converted into acetic acid, hydrogen, and carbon dioxide: $R-OH + nH_2O \rightarrow nCO_2 + nH_2 + CH_3COOH$, facilitated by Acetobacter.

Methanogenesis (Anaerobic Decomposition Step 4)

The process where acetic acid is converted to methane and carbon dioxide by Methanobacter: $CH_3COOH \rightarrow CO_2 + CH_4$.

Fossil Fuel Formation

Dead tissue undergoes partial decomposition to form coal (from plants) or natural gas and petroleum (from marine organisms), remaining out of circulation for thousands of years.

Combustion of Methane

A chemical reaction that transfers carbon from fossil fuels to the atmosphere: $CH_4 + 2O_2 \rightarrow 2H_2O + CO_2 + heat$.

Carbonic Acid Formation

Carbon dioxide in the atmosphere reacts with water in a reversible reaction to form a weak acid: $H_2O + CO_2 \rightleftharpoons H_2CO_3$.

Calcium Carbonate Shell Formation

Sea animals use dissolved ions like $Ca^{++}$ and bicarbonate liberated from rock weathering to create shells: $2HCO_3 + Ca^{++} \rightarrow CaCO_3 + H_2O + CO_2$.

Limestone Metamorphosis

Carbon is returned to the atmosphere when limestone shell accumulations react with silicon dioxide under deep-sea heat and pressure: $CaCO_3 + SiO_2 \rightarrow CaSiO_3 + CO_2$.