Nitrogen fixation is __________.

• A. the use of nitrogen to build molecules such as proteins and nucleic acids
• B. the recycling of nitrogen from organic matter in the soil
• C. the absorption of N₂ from the soil
• D. performed by fungi inhabiting root nodules
• E. the conversion of nitrogen gas in the air to a form usable by plants

Answer: (E)

Verified step by step guidance

1. Understand the concept of nitrogen fixation: It is the process by which nitrogen gas (N₂) from the atmosphere is converted into ammonia (NH₃) or related compounds, making it accessible for plants to use.
2. Recognize the role of nitrogen in biological systems: Nitrogen is essential for building molecules such as proteins and nucleic acids, but plants cannot use nitrogen gas directly.
3. Identify the organisms involved in nitrogen fixation: This process is primarily carried out by certain bacteria, including those in the genus Rhizobium, which often form symbiotic relationships with legumes, inhabiting root nodules.
4. Differentiate nitrogen fixation from other nitrogen processes: Recycling of nitrogen from organic matter and absorption of nitrogen from the soil are distinct processes that do not involve the conversion of atmospheric nitrogen gas.
5. Conclude that nitrogen fixation is the conversion of nitrogen gas in the air to a form usable by plants, which is not performed by fungi but by specific bacteria.