Problem 7 - Biology: The Dynamic Science

Question

Nitrogen fixation converts: a. atmospheric molecular nitrogen to ammonia. b. nitrates to nitrites. c. ammonia to molecular nitrogen. d. ammonia to nitrates. e. nitrites to nitrates.

Step-by-Step Solution

Answer

The correct answer is a. atmospheric molecular nitrogen to ammonia.

Step 1: Understanding Nitrogen Fixation

Nitrogen fixation is a process by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3). This chemical process is part of the nitrogen cycle, where nitrogen is taken from its relatively inert molecular form in the atmosphere and converted into ammonia, nitrites, or nitrates, which can be used by plants for growth and development.

Step 2: Identify Which Conversion is Nitrogen Fixation

Going through all the conversions listed in the options (a. atmospheric molecular nitrogen to ammonia, b. nitrates to nitrites, c. ammonia to molecular nitrogen, d. ammonia to nitrates, e. nitrites to nitrates), the first one is the definition of nitrogen fixation. Nitrogen fixation refers to the conversion of atmospheric molecular nitrogen into ammonia.

Key Concepts

Nitrogen Cycle

The nitrogen cycle is a fundamental ecological process that circulates nitrogen through the atmosphere, soil, and living organisms. It consists of several key phases which include nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

• **Nitrogen Fixation**: This initial step converts inert atmospheric nitrogen ( _{2} ) into usable forms like ammonia ( NH_{3} ) through biological or abiotic means.
• **Nitrification**: This process oxidizes ammonia into nitrites ( NO_{2}^{-} ) and then into nitrates ( NO_{3}^{-} ) by bacteria, making it available to plants.
• **Assimilation**: Plants absorb nitrates or ammonia to build proteins, nucleic acids, and other nitrogenous compounds.
  
• **Ammonification**: Decomposing bacteria convert organic nitrogen from dead organisms or waste back into ammonia.
• **Denitrification**: Finally, this process converts nitrates back into nitrogen gas, releasing it into the atmosphere and completing the cycle.

The nitrogen cycle is vital for maintaining ecosystem productivity as it ensures the availability of nitrogenous compounds necessary for plant and animal life.

Ammonia

Ammonia ( NH_{3} ) is a crucial nitrogen compound that serves as a building block for biosynthesis in plants and animals. It is produced naturally by:

• **Nitrogen Fixation**: Through the action of microorganisms like bacteria, atmospheric nitrogen is converted into ammonia, making it accessible to plants.
• **Decomposition**: As organic matter decomposes, ammonia is released back into the environment to re-enter the nitrogen cycle.

Ammonia is essential in agriculture as it forms the basis for fertilizers that enhance plant growth. However, it needs to be carefully managed since excess ammonia can lead to soil and water pollution.
To reduce ammonia emissions and improve its use in agriculture:

• **Efficient Fertilizer Use**: Applying fertilizers at specific times and rates helps reduce ammonia loss.
• **Proper Waste Management**: Managing livestock waste reduces ammonia release into the atmosphere.

Atmospheric Nitrogen Conversion

Atmospheric nitrogen conversion is an essential process that transforms nitrogen gas ( N_{2} ) from the air into forms usable by plants and other organisms. This conversion predominantly occurs through:

• **Biological Nitrogen Fixation**: Carried out by certain bacteria and archaea, these microorganisms possess an enzyme called nitrogenase, allowing them to convert N_{2} into ammonia.
• **Industrial Processes**: The Haber-Bosch process artificially fixes nitrogen at high temperatures and pressures to produce ammonia for fertilizers.
• **Lightning**: A more natural, although less significant, method where atmospheric nitrogen is converted into nitrates by the energy from lightning strikes, followed by its absorption by plants.

Through these methods, atmospheric nitrogen becomes part of the terrestrial ecosystem, underpinning the growth of plants and thereby supporting life. This conversion is vital as nitrogen is a limiting nutrient in many ecosystems, directly impacting productivity and biodiversity.