Answer: Nod factors produced by Rhizobium in response to flavonoids secreted by the legume root trigger root hair curling and infection thread formation.
- A Infection occurs entirely at random throughout the root system, without any specific chemical signaling exchanged between the two partners at all
- B Nod factors produced by Rhizobium in response to flavonoids secreted by the legume root trigger root hair curling and infection thread formation
- C The legume root itself produces antibiotic compounds specifically designed to attract Rhizobium bacteria from the surrounding soil
- D Rhizobium bacteria mechanically penetrate root cells directly, without using any form of chemical signaling whatsoever between the partners
Correct answer: B. Nod factors produced by Rhizobium in response to flavonoids secreted by the legume root trigger root hair curling and infection thread formation
Explanation: Legumes secrete flavonoids that trigger Rhizobium to produce lipopolysaccharide Nod factors. These Nod factors induce root hair curling, cortical cell division, and infection thread formation, leading to nodule development and establishment of nitrogen-fixing symbiosis.
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