Nitrogen Cycle Processes Overview

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Questions and Answers

What is the primary process through which nitrogen-fixing bacteria convert atmospheric nitrogen into a usable form for plants?

Nitrification
Ammonification
Nitrogen fixation (correct)
Denitrification

Which type of bacteria is responsible for converting ammonia into nitrites during nitrification?

Rhizobium
Nitrosomonas (correct)
Pseudomonas
Nitrobacter

In the nitrogen cycle, what form of nitrogen do plants primarily absorb?

Nitrites (NO₂⁻)
Nitrates (NO₃⁻) (correct)
Nitrogen gas (N₂)
Ammonium (NH₄⁺)

What is the main role of decomposers like bacteria and fungi in the nitrogen cycle?

Release nitrogen back into the soil as ammonia (A)

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Which process completes the nitrogen cycle by converting nitrates back into atmospheric nitrogen?

Denitrification (A)

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What impact do nitrogen-based fertilizers have on aquatic ecosystems?

They cause eutrophication, leading to pollution. (A)

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How does burning fossil fuels affect the nitrogen cycle?

It releases nitrogen oxides, contributing to air pollution. (D)

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What is the primary consequence of land use changes like deforestation on the nitrogen cycle?

Altered microbial communities and nitrogen availability. (A)

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Flashcards

Nitrogen Fixation

Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃) or ammonium ions (NH₄⁺), making it usable by plants. This process is essential for life on Earth, as nitrogen is a key component of proteins, DNA, and other vital molecules.

Nitrification

Ammonia in the soil is converted into nitrites (NO₂⁻) by Nitrosomonas bacteria, and then further oxidized into nitrates (NO₃⁻) by Nitrobacter bacteria. Nitrates are the most common form of nitrogen absorbed by plants.

Assimilation

Plants take up nitrates or ammonium from the soil and use them to build proteins and other essential compounds. Animals get their nitrogen by eating plants or other animals.

Ammonification

When organisms die, decomposers like bacteria and fungi break down organic matter, releasing nitrogen back into the soil as ammonia or ammonium. This replenishes the soil's nitrogen supply.

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Denitrification

In oxygen-limited environments, denitrifying bacteria convert nitrates back into nitrogen gas, which is released into the atmosphere. This completes the nitrogen cycle.

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Human Impact on Nitrogen Cycle

Human activities like excessive fertilizer use, burning fossil fuels, and deforestation can disrupt the natural balance of nitrogen in the environment, leading to various problems.

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Nitrogen Cycle

The continuous movement of nitrogen through different forms and compartments in the environment.

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Nitrogen Fixation (Simplified)

The process of converting atmospheric nitrogen into a form that can be used by living organisms.

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Study Notes

Nitrogen Fixation

Certain bacteria and organisms, including those in legume roots, convert atmospheric nitrogen (N₂) into ammonia (NH₃) or ammonium ions (NH₄⁺). This is called nitrogen fixation.
Lightning can also fix nitrogen, creating nitrogen oxides (that become usable forms like nitrate (NO₃⁻)).

Nitrification

Nitrifying bacteria (like Nitrosomonas) convert ammonia into nitrites (NO₂⁻).
Other nitrifying bacteria (like Nitrobacter) convert nitrites into nitrates (NO₃⁻).
Plants primarily absorb nitrates, making them essential.

Assimilation

Plants absorb nitrates or ammonium from the soil to build essential compounds like proteins.
Animals get nitrogen by consuming plants or other animals, and incorporate it into their own biological molecules (proteins and DNA).

Ammonification (Decomposition)

When organisms die, decomposers (bacteria and fungi) break down organic matter, releasing nitrogen as ammonia (NH₃) or ammonium (NH₄⁺).
This released nitrogen can be utilized by plants or further processed.

Denitrification

In oxygen-poor environments (like waterlogged soil), denitrifying bacteria convert nitrates (NO₃⁻) back into nitrogen gas (N₂).
This released nitrogen gas returns to the atmosphere, completing the cycle.

Human Impact

Excessive use of nitrogen fertilizers can lead to nitrate runoff, harming aquatic ecosystems (eutrophication) and contaminating water sources.
Burning fossil fuels and industrial processes release nitrogen oxides (NOₓ), causing air pollution and acid rain.
Changes in land use (e.g., deforestation) disrupt this natural cycle.