Biogeochemical Cycles

___________ is the most abundant gas in our atmosphere at 78%.

• Oxygen

• Carbon Dioxide

• Phosphorus

• Nitrogen

_______________ found in the soil and roots of plants "fix" nitrogen through the process called nitrogen fixation.

Nitrogen can't be used directly from the atmosphere.

• True

• False

Process in which nitrifying bacteria change ammonia into nitrites and then nitrates so that plants can absorb the nitrogen.

• Denitrification

• Nitrification

• Nitrogen Fixation

• Decomposition

Process by which animals obtain and digest nutrients by consuming plants or other animals.

• Assimilation

• Excretion

• Decomposition

• Respiration

Process by which decomposers break down dead plants and animals and return the nutrients to the soil.

• Respiration

• Decomposition

• Assimilation

• Leaching

Process by which nutrients are returned to the soil through waste products.

• Excretion

• Weathering

• Respiration

• Combustion

Process by which bacteria convert nitrogen compounds in the soil back into atmospheric nitrogen.

• Nitrification

• Denitrification

• Combustion

• Assimilation

Process by which fossil fuels are burned and CO2 is released back into the atmosphere.

• Decomposition

• Ammonification

• Combustion

• Photosynthesis

Process where plants take in CO2 from the atmosphere to make their own food.

• Respiration

• Combustion

• Nitrification

• Photosynthesis