Question

Azotobacter and Bacillus polymyxa are examples of
A) Decomposers
B) Non-symbiotic nitrogen fixer
C) Symbiotic nitrogen fixer
D) Pathogenic bacteria

Answer 1

Hint: Bacteria, fungi and moulds are decomposers or reducers of the ecosystem.They obtain their food by breaking the dead plants and animals into simple compounds which are released in the atmosphere and are utilized by producers for the synthesis of organic food.The decomposers are also called micro consumers.

Complete Answer:
- Non symbiotic nitrogen fixers are free- living bacteria,such as Azotobacter and Bacillus polymyxa are soil bacteria.they fix free nitrogen of the air and enrich the soil. This nitrogen is utilised by the crops like cereals, millets, fruits and vegetables. With cotton, rice, maize and jowar plants, Azotobacter results in increased yield and there is a saving of nitrogenous fertilizer upto 10-25 kg per hectare.

- Symbiotic nitrogen fixers are bacteria one of which is Rhizobium which forms root nodules in the legume plants and fixes atmospheric nitrogen. Within the root nodules,these bacteria fix atmospheric nitrogen in the presence of leghaemoglobin. Cultures of Rhizobium are raised in the laboratory for inoculating the seeds of legumes before sowing. This ensures development of root nodules in the seedling at an early stage, thus providing better nitrogen fixation and higher yields. After harvesting the crop,roots of legume crops are allowed to decay in the soil.This enriches the soil with nitrogenous compounds.

- Pathogenic bacteria are capable of causing disease on entering into the body which can spread through water, air, soil and also through physical contact. Mostly bacteria are harmless and beneficial but some are pathogenic and cause communicable disease. Plasmodium and Wuchereria are examples of pathogenic bacteria.

Hence option B: Non symbiotic nitrogen fixer is the correct option.

Note: Both Azotobacter and Bacillus polymyxa can be raised in the laboratory. The Azotobacter can be multiplied by using 2 ways, Fermenter and shaker.