Biogeochemical Nutrient Cycles Flashcards

Which step in the nitrogen cycle converts ammonium (NH₄⁺) to nitrate (NO₃⁻) and is carried out by specialized bacteria?

Answer: Nitrification

Nitrification is a two-step aerobic process in which bacteria like Nitrosomonas and Nitrobacter oxidize ammonium to nitrite, then nitrate.

The ocean acts as a net carbon sink primarily because of the:

Answer: Biological pump driven by phytoplankton photosynthesis and sinking organic matter

The biological pump describes how phytoplankton fix CO₂ through photosynthesis, and when they die, organic carbon sinks to the deep ocean.

In a forest ecosystem, mycorrhizal fungi play a critical role in which nutrient cycle?

Answer: Phosphorus and nitrogen uptake by plants

Mycorrhizal fungi dramatically increase the root surface area of plants, greatly enhancing uptake of phosphorus and nitrogen from soil.

Which human activity has most significantly disrupted the global phosphorus cycle?

Answer: Mining phosphate rock for fertilizer and detergents

Mining phosphate rock and applying it as fertilizer transfers phosphorus from geological reserves to agricultural and aquatic systems at unprecedented rates.

Nitrous oxide (N₂O) is an important greenhouse gas produced during which microbial process?

Answer: Nitrification and denitrification

N₂O is released as a byproduct during nitrification and as an intermediate in denitrification, particularly in moist, nitrogen-rich soils.

The residence time of carbon in fossil fuels is best described as:

Answer: Millions of years

Carbon in fossil fuels has been stored for millions of years as the organic remains of ancient organisms were compressed under heat and pressure.

What is the role of detritivores in biogeochemical cycles?

Answer: Break down dead organic matter, releasing nutrients for recycling

Detritivores such as earthworms and millipedes physically break down detritus, increasing surface area for microbial decomposers to release nutrients.