Question

What kind of micro-organisms are nitrogen fixing bacteria?
1. Rhizobium
2. Prokaryotic
3. Azotobacter
4. Cyanobacteria

Answer 1

Correct Answer - Option 2 : Prokaryotic

The correct answer is Prokaryotic.

• PROKARYOTIC BACTERIA
  • An organism without a well-defined nucleus is termed a prokaryote.
  • The word 'prokaryote' is derived from the Greek words 'pro' which means 'before' and 'karyon' which 'nut' or 'kernel'.
  • Prokaryotes lack membrane-bound organelles found in eukaryotes.
  • Prokaryotes reproduce by an asexual form of reproduction.
  • Prokaryotes include bacteria and cyanobacteria (blue-green algae).
  • Nitrogen Fixation - Conversion of atmospheric nitrogen into nitrates so that it can be utilized by plants is termed nitrogen fixation.
  • The ability of nitrogen fixation is possessed only by certain prokaryotes containing an enzyme complex called dinitrogenase that catalyzes the reduction of dinitrogen to ammonia. eg: Rhizobium, Azotobacter, Clostridium, Beijerinckia, etc.
  • The prokaryotes either fix nitrogen symbiotically (by living in the cells of higher plants) or non-symbiotically (by living freely in the soil).

• RHIZOBIUM
  • It is a symbiotic nitrogen-fixing bacteria. 
  • Rhizobium is found in the nodules of legumes and is responsible for nitrogen fixation. This was discovered in 1886 by the German physiologists Heleriegal and Wilfarth.
• AZOTOBACTER
  • It is a non-symbiotic nitrogen-fixing bacteria.
  • These are gram-negative, aerobic, free-living soil microbes that play an important role in the nitrogen cycle.
• CYANOBACTERIA
  • The common name of cyanobacteria is 'blue-green algae'.
  • These are photosynthetic bacteria containing flattened sacs called thylakoids.
  • Some cyanobacteria possess the ability of nitrogen-fixation in anaerobic conditions by means of specialized cells called heterocysts.