Free Ecology Biogeochemical Cycles Questions and Answers 1

Question 1

In the nitrogen cycle, which process is responsible for converting atmospheric nitrogen (N2), a form unusable by most plants, into ammonia (NH3), making it available to the ecosystem?

Accepted Answer

Nitrogen Fixation

Answer

Nitrogen fixation is the crucial process where atmospheric nitrogen (N2) is converted into ammonia (NH3) by certain bacteria (like Rhizobium) or through industrial processes and lightning. This conversion is essential because most organisms cannot utilize the abundant N2 gas directly.

Question 2

A significant increase in agricultural fertilizer runoff into a local lake leads to an algal bloom, followed by a sharp decline in dissolved oxygen and a subsequent fish kill. This entire process is known as:

Accepted Answer

Eutrophication

Answer

Eutrophication is the process where a body of water becomes overly enriched with minerals and nutrients, which induces excessive growth of algae. When the algae die and decompose, the process consumes large amounts of dissolved oxygen, leading to hypoxic conditions that can kill fish and other aquatic organisms.

Question 3

Unlike the carbon and nitrogen cycles, the phosphorus cycle lacks a significant atmospheric component. What is the primary reservoir for phosphorus?

Accepted Answer

Sedimentary rock

Answer

The vast majority of Earth's phosphorus is stored in rocks and sediments. The cycle begins with the weathering of these rocks, which slowly releases phosphate into soils and water, making it available to organisms. There is no major gaseous form of phosphorus.

Question 4

Which of the following human activities is the most significant driver of the recent, rapid increase of carbon dioxide in the atmospheric reservoir of the carbon cycle?

Accepted Answer

Combustion of fossil fuels

Answer

The burning of fossil fuels (coal, oil, and natural gas) for energy has dramatically increased the concentration of carbon dioxide in the atmosphere. This process rapidly moves carbon from the long-term reservoir in rocks and sediments (geosphere) to the atmospheric reservoir.

Question 5

In an agricultural field with waterlogged, anaerobic soil, a farmer notices that despite applying nitrate-based fertilizer, the nitrogen availability for crops is decreasing. Which microbial process is most likely responsible for this loss of usable nitrogen?

Accepted Answer

Denitrification

Answer

Denitrification is a process carried out by bacteria in anaerobic (low-oxygen) conditions, such as waterlogged soil. These bacteria convert nitrates (NO3-) back into nitrogen gas (N2), which is then lost to the atmosphere and becomes unavailable to plants.

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Ecology Practice Test

Free Ecology Biogeochemical Cycles Questions and Answers 1