Presentation 3: Carbon Cycle

Science, ecology, MYP5

Carbon Cycle

The biogeochemical cycle by which carbon is exchanged among the major reservoirs on Earth: the atmosphere, oceans, land (including fossil fuels and sedimentary rock), and living organisms (biomass).

Carbon Reservoirs (Sinks)

Places where carbon is stored. Major reservoirs include: The atmosphere (as CO₂), the oceans (as dissolved CO₂ and hydrogen carbonate ions), biomass of plants and animals, fossil fuels (coal, oil, gas), and sedimentary rocks like limestone.

Carbon Fixation (by Autotrophs)

The process where autotrophs, through photosynthesis, absorb carbon dioxide from the atmosphere or water and convert it into organic compounds like carbohydrates. This sets up a concentration gradient that helps CO₂ diffuse into the autotrophs.

Dissolved Carbon Dioxide

In aquatic ecosystems, carbon is present as dissolved CO₂. CO₂ combines with water to form carbonic acid (H₂CO₃), which then dissociates into hydrogen (H⁺) and hydrogen carbonate ions (HCO₃⁻). This process lowers the pH of the water.

Respiration

A process carried out by all living organisms (including plants) that breaks down organic compounds to release energy, producing carbon dioxide as a waste product. This CO₂ then diffuses out of the organism into the atmosphere or water.

Methanogens

Bacteria that produce methane (CH₄) from organic matter in anaerobic conditions (environments without oxygen). They are found in places like swamps, lake beds, landfills, and the guts of ruminant animals.

Methane Oxidation

In the atmosphere, methane is oxidized (reacts with oxygen) to produce carbon dioxide and water.

Peat

Partially decomposed organic matter that accumulates in acidic and/or anaerobic conditions, typically in waterlogged soils where decomposers cannot function effectively. Peat is the first step in the formation of coal.

Fossil Fuels

Carbon

Combustion

The process of burning biomass (like in a forest fire) or fossil fuels, which rapidly releases large amounts of stored carbon into the atmosphere as carbon dioxide.

Calcium Carbonate (CaCO₃)

A compound used by marine organisms like corals and molluscs to build their hard shells and exoskeletons. When these organisms die, their remains can accumulate and form limestone, a sedimentary rock that acts as a major long