Answer: Anabaena fixes N2 providing it to Azolla which provides carbon through photosynthesis.
- A Azolla fixes atmospheric N2 directly while Anabaena supplies it with photosynthates instead
- B Anabaena fixes N2 providing it to Azolla which provides carbon through photosynthesis
- C Both Azolla and Anabaena independently fix nitrogen on their own without cooperating at all
- D Azolla supplies dissolved soil minerals while Anabaena instead supplies water uptake support
Correct answer: B. Anabaena fixes N2 providing it to Azolla which provides carbon through photosynthesis
Explanation: In the Anabaena-Azolla symbiosis, Anabaena (a cyanobacterium in leaf cavities) fixes atmospheric N2 using heterocysts, providing fixed nitrogen to Azolla, while Azolla provides carbohydrates through photosynthesis.
Sewage passes through physical removal (primary), then aerobic biological treatment where microbes form flocs that consume organic matter (secondary); the settled activated sludge is then digested anaerobically to produce biogas - a deliberate switch from aerobic to anaerobic conditions between stages.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers