Question

Symbiotic nitrogen fixing bacteria are found in -
A. Azolla
B. Gnetum
C. Anthoceros
D. Cycas
E. Riccia
Choose the correct answer from the options given below :

• A. A, C and D Only
• B. B, C and E Only
• C. C, D and E Only
• D. B, C and D Only

Hint:

Remember these key examples of N-fixing symbiosis: Legumes with {Rhizobium}, {Azolla} with {Anabaena}, and {Cycas} (coralloid roots) and {Anthoceros} with cyanobacteria like {Nostoc}.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question asks to identify which of the listed plants form a symbiotic relationship with nitrogen-fixing microorganisms (specifically bacteria or cyanobacteria).
Step 2: Detailed Explanation:
Let's examine each plant:
A. Azolla: This is an aquatic fern that has a well-known symbiotic relationship with the nitrogen-fixing cyanobacterium Anabaena azollae, which lives in cavities of its leaves. This makes Azolla a potent biofertilizer in rice paddies. (Correct)
B. Gnetum: This is a gymnosperm that does not form symbiotic relationships for nitrogen fixation. (Incorrect)
C. Anthoceros: This is a hornwort (a bryophyte) that has cavities in its thallus which are colonized by the nitrogen-fixing cyanobacterium Nostoc. (Correct)
D. Cycas: This is a gymnosperm (a cycad) that possesses specialized roots called 'coralloid roots'. These roots are negatively geotropic and house symbiotic nitrogen-fixing cyanobacteria, such as Nostoc or Anabaena. (Correct)
E. Riccia: This is a liverwort (a bryophyte) that does not have symbiotic nitrogen-fixing associations. (Incorrect)
Step 3: Final Answer:
The plants with symbiotic nitrogen-fixing bacteria are Azolla, Anthoceros, and Cycas. Therefore, the correct option is A, C, and D only.