Microbes in Production of Biogas as Biocontrol Agents & Biofertilisers

1 Mark Questions

1. Name the type of association that the genus Glomus exhibits with higher plants. [All India 2014] Ans. The genus Clomus exhibits symbiotic association with higher plants.
2. State one reason for adding blue-green algae to the agricultural soil. [Delhi 2014C] or

Mention two advantages of adding blue-green algae to paddy fields. [All India 2011C]

Ans. Blue-green algae are added to agricultural soil because they add organic matter to the soil and also increase its fertility.

1. Mention the role of cyanobacteria as biofertilisers. [AilIndia 2012] Ans. Role of cyanobacteria as biofertilisers Cyanobacteria fix atmospheric nitrogen and increases the organic matter of the soil through their photosynthetic activity,
2. Name any one symbiont, which serve as biofertiliser. Mention it specific role. [All India 2010C]

Ans. Rhizobium is a symbiont bacteria that serve as biofertiliser The bacteria fix the atmospheric nitrogen into organic forms, which is used by the plants as nutrients.

1. Which of the following is a free-living bacteria that can fix nitrogen in the soil? Spirulina, Azospirillum and Sonalika. [Delhi 2009] Ans. Azospirillum
2. Which of the following is a cyanobacterium that can fix atmospheric nitrogen? Azospirillum, Oscillatoria and Spirulina. [All India 2009]

Ans. Oscillatoria

7. How is the presence of cyanobacteria in the paddy fields beneficial to rice crop? [Delhi 2009C]

Ans. In the paddy fields, cyanobacteria such as blue-green algae fix atmospheric nitrogen to enrich the nitrogen content of soil. Therefore, the entire need of nitrogen to rice crop can be supplied by blue-green algae, leading to increase in yield.

8. Name the group of organisms and the substrate that act on to produce biogas. [Delhi 2009]

Ans. Methanogens are the group of organisms that acts on cellulosic materials/cow dung to produce biogas.

2 Marks Questions

9. How do mycorrhizae act as biofertilisers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants. [Delhi 2012]

Ans. Fungi form symbiotic association with plants, which is called mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes itto the plant. Thus, acts as a biofertiliser. The fungi belonging to the genus Glomus form mycorrhizal associations with plants.

10. How do methanogens help in producing biogas? [Delhi 2012]

Ans. Methanogens grow anaerobically on cellulosic material and produce large amount of methane along with CO₂ and H₂. Since, biogas is a mixture of methane and CO₂, methanogens helps in its production

11. Why is Rhizobium categorised as a symbiotic bacterium? How does it act as biofertilisers? [Delhi 2012]

Ans. The nodules on the roots of leguminous plants are formed by Rhizobium bacteria for their survival. These bacteria fix atmospheric nitrogen into organic form, which is used by the plant as nutrients. Since, Rhizobium forms symbiotic association with leguminous plants these are considered as symbiotic bacteria, (I) Rhizobium fixes the atmospheric nitrogen into organic form, i.e. nitrates which can be utilised by the plant as nutrient. So, it is used as biofertilisers.

12. How do plant benefit from having mycorrhizal symbiotic association?

[Foreign 2010]

Ans. The plants get benefits from mycorrhizal symbiotic association in the following two ways:

1. The fungal symbiont in mycorrhizal associations absorb phosphorus from soil and passes it to the plant.
2. It also provides resistance to root borne pathogens and increases plant growth and development.

13. What are methanogens? Name the animals in which methanogens occur and the role they play there.[Delhi 2014]

Ans. Methanogens are groups of anaerobic bacteria, that produces large amount of methane. Methanogens are found in rumen of cattle and intestine of humans.

The methanogens present in intestine of animals and humans act on cellulosic part of food and digests them, thereby releasing methane along with <math>C0_2</math> and <math>H_2</math>.

1. How are baculoviruses and Bacillus thuringiensis used as biocontrol agents? Why are