Question

Which of the following organisms cannot fix nitrogen? A. Azotobacter
B. Oscillatoria
C. Anabaena
D. Volvox
E. Nostoc
Choose the correct answer from the options given below:

• A. D only
• B. B only
• C. E only
• D. A only

Hint:

Many cyanobacteria, like Anabaena and Nostoc, have specialized cells called heterocysts that help them fix nitrogen. Organisms like Volvox do not possess this ability.

Answer 1

The Correct Option is A

Let's analyze the organisms: A. Azotobacter is a nitrogen-fixing bacterium, so it can fix nitrogen.
B. Oscillatoria is a type of cyanobacteria (blue-green algae) and can fix nitrogen.
C. Anabaena is also a nitrogen-fixing cyanobacterium.
D. Volvox is a green alga that cannot fix nitrogen. It relies on the environment for nitrogen and does not have the ability to fix it.
E. Nostoc is a nitrogen-fixing cyanobacterium. Thus, the correct answer is D only.