Nitrogen fixing bacteria-anabaena-are found in the plant ______.

A. Azolla leaves

B. Cycas coralloid roots

C. Anthoceros body.

D. All of these.

Nitrogen fixation is the process through which atmospheric nitrogen (N₂) is converted into a usable form like ammonia, either naturally or industrially. Certain bacteria, such as Anabaena, a filamentous cyanobacterium, are well-known for their nitrogen-fixing ability. These bacteria often form symbiotic relationships with specific plants, supplying them with essential nitrogen.

Let’s examine the given options:

• Azolla: This aquatic fern floats on water with small, overlapping scale-like leaves, and its roots hang freely. It forms a symbiotic association with the cyanobacterium Anabaena azollae, which fixes atmospheric nitrogen and provides it to the plant as an essential nutrient.
• Cycas: Cycas plants have unbranched, coral-like coralloid roots that host nitrogen-fixing cyanobacteria like Anabaena. The plant supplies carbon to these bacteria, and in return, they fix nitrogen that supports the plant’s growth. The bacteria act as endosymbionts within the roots.
• Anthoceros: This thalloid bryophyte has lobed bodies with dichotomous branching. Anabaena is the only cyanobacterium found in Anthoceros, performing symbiotic nitrogen fixation within its tissues.

Conclusion: All the above plants—Azolla, Cycas, and Anthoceros—host nitrogen-fixing cyanobacteria.

Correct Answer:D. All of these