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Which type of organism is known for utilizing nitrogen directly from the air?
Blue-green algae
Fungi
Bacteria
Protozoans
The correct answer is: Blue-green algae
Blue-green algae, also known as cyanobacteria, are known for their ability to fix atmospheric nitrogen. This process involves converting nitrogen gas (N2) from the air into a more usable form, such as ammonia (NH3), which can then be utilized by plants and other organisms in the ecosystem. Cyanobacteria possess specialized cells called heterocysts that provide the necessary anaerobic environment for the nitrogen-fixing process to occur, despite being photosynthetic and requiring oxygen for photosynthesis. While fungi, bacteria, and protozoans each play important roles in nutrient cycles and can interact with nitrogen in various ways, they do not have the same capability to directly utilize atmospheric nitrogen in the manner that blue-green algae do. Some bacteria (specifically, certain kinds like Rhizobium) can also fix nitrogen, but the question specifically highlights organisms known for directly extracting nitrogen from the air, which aligns more closely with blue-green algae.