2.3 Biogeochemical Cycles (DP IB Environmental Systems & Societies (ESS): HL): Flashcards

Human disruption of biogeochemical cycles can cause environmental imbalances and threaten the sustainability of ecosystems.

The carbon cycle is the process by which carbon moves between the abiotic and biotic components of an ecosystem.

Materials must be recycled so that the building blocks for future organisms are available and to ensure elements like carbon are reused.

False.

There is a finite amount of carbon on Earth, so it must be recycled to support life.

Carbon is constantly being recycled around the biosphere so that the total amount of carbon in the biosphere is essentially constant.

An organic carbon store is a reservoir of carbon in the form of carbon-containing compounds in living organisms or fossil fuels.

An inorganic carbon store refers to carbon reservoirs in non-living components such as the atmosphere, soils, and oceans.

Equilibrium in a carbon store is when carbon absorption is balanced by carbon release.

The average time that a carbon atom remains in a store is called residence time.

Two key processes that transform carbon are photosynthesis (plants absorb CO₂) and cellular respiration (releases CO₂).

When fossil fuels are burned, the carbon stored within them combines with oxygen to form carbon dioxide, which is released into the atmosphere.

Carbon sequestration is the process of capturing atmospheric CO₂ and storing it in solid or liquid forms.

A forest is a sink when photosynthesis exceeds respiration, a store when input and output are balanced, and a source when it releases more carbon than it absorbs (e.g. after fire or deforestation).

A fossil fuel is a carbon-rich energy source such as coal, oil, or natural gas, formed from ancient plants and animals buried and transformed by heat and pressure over millions of years.

When humans burn fossil fuels, stored carbon is released as carbon dioxide into the atmosphere, turning the fuel from a carbon sink to a carbon source.

Fossil fuels were formed when past ecosystems acted as carbon sinks, trapping organic carbon over millions of years.

A carbon sink is a natural system that absorbs and stores more carbon than it releases, helping to reduce atmospheric carbon dioxide.

Regenerative agricultural techniques like crop rotation and no-till farming can turn soil into a carbon sink, increasing the amount of organic matter stored.

False.

Forests only act as carbon sinks when managed sustainably. Unsustainable practices like clear-cutting can turn them into carbon sources.

When fossil fuels are burned, they become carbon sources, releasing stored carbon as carbon dioxide.

Ocean acidification lowers the pH of seawater, reducing calcium carbonate deposition in shells and corals, which leads to weaker shells and less diverse reef structures.

A lithosphere carbon store is carbon held in the Earth’s crust, mainly as fossil fuels and carbonate rocks.

Carbon stored in fossil fuels includes coal, oil, and natural gas.

The residence time of carbon in fossil fuels and carbonate rocks is hundreds of millions of years.

Coal is mainly formed from dead plant material in swampy areas, especially during the Carboniferous period.

Oil and natural gas are mainly formed from marine microorganisms like plankton that settled on the seafloor and were buried in porous rocks.

Methanogenesis is the process by which methanogenic bacteria produce methane from organic matter in anaerobic conditions.

False.

Methane is a much more potent greenhouse gas than carbon dioxide, with a global warming potential about 25 times higher over 100 years.

The hard parts of reef-building corals and molluscs contain calcium carbonate, which can become fossilised in limestone.

The nitrogen cycle is the process through which nitrogen moves between organic and inorganic forms in ecosystems.

Organic nitrogen is found in proteins, DNA, and other compounds in living organisms and in dead organic matter.

Inorganic nitrogen exists in the atmosphere as nitrogen gas (N₂), and as ammonia (NH₃), nitrites (NO₂⁻), and nitrates (NO₃⁻) in soils and water.

Most of the Earth's atmosphere is made up of nitrogen gas (N₂), which accounts for about 78% of the air.

After death, organic matter decomposes, returning nitrogen to the soil.

Bacteria are essential in the nitrogen cycle because they convert nitrogen between different forms through processes like nitrogen fixation, nitrification, denitrification, and decomposition.

Nitrogen fixation by bacteria converts atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can use.

False.

Denitrification occurs in anaerobic (low oxygen) conditions, such as waterlogged soils.

Plants in waterlogged soils grow poorly because denitrification reduces the availability of nitrogen by converting nitrates into nitrogen gas, which plants cannot use.

Legumes form mutualistic relationships with nitrogen-fixing bacteria in their root nodules, allowing them to thrive in nitrogen-poor soils.

Lightning provides the energy to break nitrogen molecules in the atmosphere, forming nitrogen oxides that dissolve in rain and fall as nitrates, which plants can use.

During decomposition, bacteria break down organic nitrogen into ammonium (NH₄⁺).

The nitrogen cycle involves transfer processes (movement of nitrogen without changing form) and transformation processes (nitrogen changes its chemical form).

Eutrophication is the over-enrichment of water bodies with nutrients (such as nitrogen), leading to excessive algal growth, oxygen depletion, and harm to aquatic life.

Deforestation reduces vegetation that absorbs nitrogen, leading to increased nitrogen leaching into water bodies, which can cause pollution and disrupt freshwater ecosystems.

Excess nitrogen from fertilisers can cause eutrophication and the formation of dead zones in aquatic environments.

Agricultural runoff containing nitrogen fertilisers can lead to dead zones in aquatic environments due to algal blooms and oxygen depletion.

The Haber process is an industrial method for synthesising ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂) for use in fertilisers.

True.

The Haber process increases food production but excess nitrogen from fertilisers causes pollution and biodiversity loss.

The planetary boundaries model outlines nine critical processes that regulate Earth's system stability, one of which is the nitrogen cycle.

Crossing the nitrogen planetary boundary can lead to irreversible environmental changes, such as water pollution and loss of biodiversity.

A dead zone is an area in a water body where oxygen levels are so low that most aquatic life cannot survive, often caused by nutrient pollution.

Aquaculture introduces excess nitrogen into water through uneaten fish feed and waste, leading to algal blooms and oxygen depletion.

Urban nitrogen pollution comes from sewage, stormwater runoff, and vehicle emissions, all of which increase nitrogen levels in water bodies.

Two measures to reduce nitrogen pollution are using sustainable farming techniques (such as crop rotation and precision farming) and improving sewage treatment plants.

Precision farming is an agricultural approach that uses technology to apply fertilisers and resources efficiently to reduce environmental impact and improve yields.