Key Concepts of Biogeochemical Cycles to Know for AP Biology

Biogeochemical cycles are essential processes that recycle vital elements like carbon, nitrogen, and phosphorus through the environment. Understanding these cycles helps us grasp their impact on ecosystems, climate, and human activities, linking biology and environmental science in meaningful ways.

1. Carbon cycle

   • Carbon is a key element in organic molecules, essential for life, and cycles through the atmosphere, biosphere, hydrosphere, and geosphere.
   • Major processes include photosynthesis (carbon fixation), respiration (release of CO2), decomposition, and combustion of fossil fuels.
   • Human activities, such as deforestation and fossil fuel burning, significantly increase atmospheric CO2 levels, contributing to climate change.

2. Nitrogen cycle

   • Nitrogen is vital for amino acids and nucleic acids, and it cycles through the atmosphere, soil, and living organisms.
   • Key processes include nitrogen fixation (conversion of atmospheric N2 to ammonia), nitrification (conversion of ammonia to nitrates), and denitrification (conversion of nitrates back to N2).
   • Excess nitrogen from fertilizers can lead to water pollution and eutrophication, impacting aquatic ecosystems.

3. Water cycle (hydrologic cycle)

   • The water cycle describes the continuous movement of water through evaporation, condensation, precipitation, and runoff.
   • It plays a crucial role in regulating climate, supporting ecosystems, and providing freshwater resources for human use.
   • Human activities, such as urbanization and deforestation, can disrupt natural water flow and lead to issues like flooding and water scarcity.

4. Phosphorus cycle

   • Phosphorus is essential for DNA, RNA, and ATP, and it primarily cycles through rocks, soil, water, and living organisms.
   • Unlike other cycles, phosphorus does not have a gaseous phase; it is released through weathering of rocks and taken up by plants.
   • Excess phosphorus from agricultural runoff can lead to algal blooms and water quality issues in aquatic systems.

5. Sulfur cycle

   • Sulfur is important for proteins and vitamins, cycling through the atmosphere, lithosphere, and biosphere.
   • Key processes include the release of sulfur dioxide (SO2) from volcanic eruptions and human activities, and its conversion to sulfate ions in the atmosphere.
   • Acid rain, resulting from sulfur emissions, can harm ecosystems and damage infrastructure.

6. Oxygen cycle

   • Oxygen is essential for cellular respiration and is produced primarily through photosynthesis in plants and phytoplankton.
   • The cycle involves the exchange of oxygen between the atmosphere, biosphere, and hydrosphere, with respiration and decomposition releasing CO2.
   • Changes in land use and deforestation can impact oxygen production and carbon balance in ecosystems.

7. Rock cycle

   • The rock cycle describes the formation, breakdown, and reformation of rocks through processes like weathering, erosion, sedimentation, and metamorphism.
   • It connects geological processes with biogeochemical cycles, as rocks provide essential minerals and nutrients for ecosystems.
   • Understanding the rock cycle is crucial for studying soil formation, nutrient availability, and the impact of geological events on the environment.