Nutrient Cycles in the Biosphere

Vocabulary flashcards covering key terms and definitions related to the water, oxygen, carbon, nitrogen, sulfur, and phosphorus cycles presented in the lecture notes.

Biosphere

The global ecological system integrating all living beings and their relationships with the atmosphere, hydrosphere, and lithosphere.

Nutrient cycle

A system in which energy and matter circulate between living organisms and the non-living environment.

Water cycle (Hydrologic cycle)

Continuous movement of water through evaporation, condensation, precipitation, and collection.

Collection (water cycle)

Stage where water accumulates in ponds, lakes, rivers, and oceans before re-entering the cycle.

Evaporation

Process that turns liquid water into water vapor, driven by solar energy.

Condensation

Cooling of water vapor into liquid droplets, forming clouds.

Precipitation

Return of condensed water to Earth as rain, snow, hail, or sleet.

Oxygen cycle

Circulation of oxygen through photosynthesis, respiration, and oxidation processes.

Photosynthesis

Plant and algae process that converts CO₂ and water into glucose and releases O₂.

Cellular respiration

Process in animals and plants that breaks down glucose to release CO₂, water, and energy.

Ozone layer (O₃)

Stratospheric layer of triatomic oxygen that absorbs harmful UV radiation.

Carbon cycle

Movement of carbon among atmosphere, biosphere, oceans, and Earth’s interior.

Carbon sink

Reservoir such as oceans, forests, or soil that stores more carbon than it releases.

Fossil fuels

Carbon-rich energy sources (coal, oil, natural gas) formed from ancient organic matter.

Methane (CH₄)

Potent greenhouse gas produced by wetlands, livestock, and fossil fuel extraction.

Nitrogen cycle

Natural circulation of nitrogen among atmosphere, organisms, soil, and water.

Nitrogen fixation

Conversion of atmospheric N₂ into ammonia or ammonium by bacteria or lightning.

Lightning fixation

Atmospheric electrical discharge that converts N₂ into reactive nitrogen compounds.

Nitrification

Bacterial process that oxidizes NH₃/NH₄⁺ first to nitrites and then to nitrates.

Ammonia (NH₃)

First stable product of nitrogen fixation, toxic to most plants in high amounts.

Ammonium (NH₄⁺)

Ionized form of ammonia, usable by some plants and microbes.

Nitrites (NO₂⁻)

Intermediate nitrogen compounds produced during nitrification.

Nitrates (NO₃⁻)

Highly soluble nitrogen form most readily absorbed by plants.

Assimilation

Uptake of nitrates by plants to build proteins and DNA; passed to animals via food.

Ammonification

Decomposition process that converts organic nitrogen in dead matter to NH₃/NH₄⁺.

Denitrification

Conversion of nitrates back to N₂ gas by bacteria, releasing it to the atmosphere.

Nitrogen-fixing bacteria

Microbes (e.g., Rhizobium) that convert atmospheric N₂ into ammonia in soil or roots.

Nitrifying bacteria

Bacteria (e.g., Nitrosomonas, Nitrobacter) that drive nitrification.

Denitrifying bacteria

Anaerobic bacteria that reduce nitrates to nitrogen gas during denitrification.

Sulfur cycle

Movement of sulfur through rocks, soil, living organisms, air, and back again.

Sulfate (SO₄²⁻)

Oxidized, water-soluble sulfur form absorbed by plants.

Hydrogen sulfide (H₂S)

Toxic sulfur gas produced by anaerobic bacteria and volcanic activity.

Weathering of rocks

Breakdown of sulfur- or phosphorus-containing rocks, releasing minerals to soil and water.

Volcanic emissions (sulfur)

Release of sulfur gases (SO₂, H₂S) into the atmosphere during eruptions.

Phosphorus cycle

Slow geologic cycle moving phosphorus mainly through rocks, soil, organisms, and water.

Phosphate (PO₄³⁻)

Primary inorganic form of phosphorus utilized by plants.

Limiting nutrient

Element whose scarcity restricts biological growth; phosphorus often plays this role.

Geological uplift

Tectonic process that raises seabed–stored phosphorus-bearing rocks onto land.

Eutrophication

Nutrient over-enrichment (often from excess phosphorus) leading to algal blooms and oxygen depletion in water bodies.

Decomposer

Organism (bacteria, fungi) that breaks down dead matter, recycling nutrients back to the ecosystem.