Biogeochemical Cycles

• Nitrogen fixation is a key process where abiotic nitrogen in the air needs to be "fixed" by bacteria before it can be assimilated
• Living organisms require nitrogen to build proteins
• Living organisms also need carbon to produce all organic molecules such as sugar and fats
• CO2 in the air is an abiotic source of carbon
• Carbon sinks include fossil fuels and marine rocks, which store carbon
• Biogeochemical cycles explain how matter is used in ecosystems
• Matter is conserved within ecosystems, unlike energy
• The 4 biogeochemical cycles tested on the AP exam are: Carbon, Nitrogen, Phosphorous, and Hydrological cycles
• Carbon is the backbone of all organic molecules and is the central atom in fats, carbohydrates, and structural proteins
• Abiotic source for carbon is carbon dioxide (CO2) in the atmosphere
• If sugar in a plant or animal body does not get metabolized, it can become fossilized as fossil fuels or marine sediment
• Fossil fuels and limestone act as carbon sinks, storing CO2 in the atmosphere
• Burning fossil fuels for energy adds CO2 to the atmosphere, leading to environmental problems like climate change and ocean acidification
• Nitrogen is an essential element for structural proteins and DNA
• Living systems need large amounts of nitrogen and phosphorus to build and maintain their bodies
• Nitrogen gas in the air is inert and needs to be "fixed" by specialized bacteria before it can be absorbed by living organisms
• Fixed nitrogen can be assimilated by plants and stored in their bodies, then transferred to animals when they consume the plants
• Specialized bacteria return nitrogen to the atmosphere through denitrification
• Phosphates come from rocks and are essential for building bodies
• Plants absorb phosphates from the soil or water to build their bodies
• Phosphates are removed from the ecosystem through sedimentation, getting trapped in rocks again
• Phosphorus and nitrogen are limiting factors in ecosystems as the rate at which they are brought into living systems is slow compared to the demand
• Water cycle describes how water moves between living and non-living components of the ecosystem
• Water vapor accumulates as clouds in the atmosphere and falls out as precipitation
• Water can run-off the land, infiltrate into the soil, or evaporate back into the atmosphere
• Groundwater (aquifers) can trap water, or it can be absorbed by plants and returned to the air through transpiration
• Rainfall and evaporation rates impact the Net Primary Productivity (NPP) of ecosystems
• Water, nutrients, and sunlight are abiotic factors that determine the abundance and types of organisms in an ecosystem
• Biogeochemical cycles recycle matter between living and non-living components of ecosystems
• The Carbon Cycle: carbon is the backbone of all organic molecules
• Plants bring CO2 into living systems through photosynthesis and store it as sugar
• CO2 is returned to the air when sugar is metabolized, completing the cycle
• Carbon Cycle:

  • Sugar metabolized by plants or animals can become fossilized as fossil fuels (oil, coal, natural gas) or marine sediment (limestone)
  • Fossil fuels and limestone act as carbon sinks, lowering CO2 levels in the atmosphere
  • Burning fossil fuels releases CO2, leading to environmental issues like climate change and ocean acidification
• Nitrogen Cycle:

  • Nitrogen is essential for structural proteins and DNA in living systems
  • Nitrogen gas in the air is inert and needs to be fixed by specialized bacteria (chemotrophs) to be assimilated by plants
  • Fixed nitrogen can be obtained by animals when they eat plants, and returned to the soil/water by decomposers
  • Nitrogen is returned to the atmosphere through denitrification by specialized bacteria
• Phosphorus Cycle:

  • Phosphates are essential for building organisms' bodies
  • Phosphates come from rocks, especially Potash, and are dissolved in water and soil as rocks erode
  • Plants absorb phosphates from soil/water, animals consume plants and assimilate phosphates, and decomposers return phosphates to the soil/water
  • Phosphates are removed from the ecosystem through sedimentation, getting trapped in rocks again
• Hydrological (Water) Cycle:

  • Water vapor accumulates as clouds in the atmosphere and falls as precipitation
  • Precipitated water can run-off, infiltrate into soil, or evaporate back into the atmosphere
  • Infiltrated water can become groundwater (aquifers) or be absorbed by plants
  • Transpiration returns water to the air through plants
  • Rainfall and evaporation rates impact Net Primary Productivity (NPP) of ecosystems