Microbes in Human Welfare VBQs Class 12 Biology

VBQs for Class 12

VBQs Microbes in Human Welfare Class 12 Biology with solutions has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Biology with solutions. The following Microbes in Human Welfare Class 12 Biology value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Microbes in Human Welfare VBQs Class 12 Biology

Very Short Answer Type Questions

Question. State one reason for adding blue-green algae to agricultural soil.
Mention the role of cyanobacteria as a biofertilizer.
Answer :
 Blue-green algae are cyanobacteria. They fix atmospheric free nitrogen. Therefore, they increase soil fertility and also add the organic matter to the soil. 

Question. What makes Nucleopolyhedrovirus a desirable biological control agent ?
Answer :
 Nucleopolyhedrovirus is the genus of baculoviruses.
They are quite effective biocontrol agent. Its specificity makes it a desirable biocontrol agent.
They selectively attack insect and other arthropods.
They are suitable for species specific, narrow spectrum insecticidal application. They do not harm non-target organisms. They are also desirable in IPM programme to conserve beneficial insects.

Question. Mention two advantages of adding blue-green algae to paddy fields.
Answer :
 In paddy fields, cyanobacteria (blue-green algae) add organic matter to the soil and increases its fertility. 

Question. Which of the following is a cyanobacterium that can fix atmospheric nitrogen. Azospirillum, Oscillatoria, Spirulina. 
Answer :

Short Answer Type Questions

Question. Name a free-living symbiotic bacterium that serve as bio-fertilizer. Why are they so called?
Answer :
 Azospirillum/Azotobacter, Rhizobium.
They enrich soil nutrient/nitrogen fixation.
Detailed Answer :
Rhizobium leguminosarum is a symbiotic bacterium found in the root nodules of leguminous plants that has the ability to fix atmospheric nitrogen.
Azospirillum and Azotobacter are free-living bacteria found in the soil. They enrich soil with the nitrogen contents.

Question. Why is Rhizobium categorized as a ‘symbiotic bacterium’ ? How does it act as a biofertiliser ?
Answer :
 Rhizobium is a symbiotic bacterium living in the root nodule of leguminous plants, it fixes atmospheric nitrogen into organic forms to be used by plants as nutrient and in turn bacteria get carbohydrate food and shelter from the plant.
It is a biofertiliser as it is a living organism that enriches nutrient content of the plant / soil. 

Question. How does the application of the fungal genus, Glomus, to the agricultural farm increase the farm output ? 
Answer :
 Glomus forms mycorrhizal association, absorbs phosphorus, provide resistance to root borne pathogens, enhanced to tolerate salinity / drought.

Question. Your advice is sought to improve the nitrogen content of the soil to be used for cultivation of a non-leguminous terrestrial crop.
(a) Recommend two microbes that can enrich the soil with nitrogen.
(b) Why do leguminous crops not require such enrichment of the soil?
Answer :
 (a) Azospirillum/ Azotobacter/ Anabaena/ Nostoc / Oscillatoria /Frankia (Any two correct names of microbes). 
(If cyanobacteria mentioned=, but if along with cyanobacteria-Anabaena / Nostoc / Oscillatoria mentioned then No mark on cyanobacteria).
(b) They can fix atmospheric nitrogen, due to presence of Rhizobium/N2 fixing bacteria in their root nodules. 

Question. (i) How do organic farmers control pests ? Give two examples.
(ii) State the difference in their approach from that of conventional pest control methods.
Answer :
 (i) Natural predation / biological control. 
Examples – lady bird used to kill aphids / dragon flies used to kill mosquitoes / Bacillus thuringiensis used to kill cotton bollworm / caterpillar / butterfly caterpillar. (Any two)

Conventional Pest ControlOrganic farming based pest control
(a) Use of chemical insecticides and pesticides.No chemical used.
(b) Harmful to non target organisms.Not harmful to non target organisms.
(c) Cause environmental pollution.No adverse impact on environment.

Detailed Answer :
(i) Organic farmers control pests by utilising natural predation instead of introducing or applying chemicals. Microbial biocontrol agents are the species – specific pesticides.
The examples include :
(a) Bacillus thuringiensis : This is a bacterium which produces a toxin that specifically kills insect larvae of cotton bollworm such as lepidopterans, coleopterans and dipterans leaving aside all other non-targeted organisms.
(b) Trichoderma sp. which is free living fungus and works as a bio-control agent against several plants pathogens.
(ii) Conventional pest control methods use chemicals. They are non specific, cause harm to non target beneficial organisms and pore problems like environmental pollution and biological magnification, where as organic farmers control pest by biocontrol agents. They are specific, do not harm non target organism and do not cause pollution. Moreover, as compared to conventional pest control methods, organic farmers do not try to completely get rid of pests but keep them at manageable levels.
They believe that complete eradication of pests is not beneficial and has certain adverse effects.
It leads to death of those beneficial creatures that are dependent on them for food.

Question. Choose any three microbes, from the following which are suited for organic farming which is in great demand these days for various reasons.
Mention one application of each one chosen.
Mycorrhiza; Monascus; Anabaena; Rhizobium; Methanobacterium; Trichoderma.
Answer : 
Mycorrhiza : Fungal symbiont of the association.
absorb phosphorus from soil.
Anabaena : Fix atmospheric nitrogen / Adds organic matter to the soil.
Rhizobium : It is a symbiotic root nodule bacterium which fixes atmospheric nitrogen (in leguminous plants) in organic form which is used by plant as nutrient.
Methanobacterium : They digest cellulosic material and the product / spent slurry can be used as fertilizer.
Trichoderma : Biocontrol agent for several plant pathogens.

Question. How are Baculoviruses and Bacillus thuringiensis used as bio-control agents? Why are they preferred over readily available chemical pesticides.
Answer : 
Baculoviruses belong to Nucleopolyhedroviruses.
They are used as biocontrol agents and preferred over readily available chemical pesticides because they are species specific and have narrow spectrum insecticidal application. They do not harm the non target organisms.
Bacillus thuringiensis is a bacterium and is a biocontrol agent against cotton bollworm insects.
They produce a toxin that specifically kill the insect larvae when the toxin is released in their gut. It is also preferred over chemical pesticides because it is specific and does not have any negative role over non target organisms. Moreover, the biopesticides are inexpensive and do not cause environmental pollution. 

Question. What are biopesticides ? Give the scientific name and use of the first commercially used biopesticide in the world. 
Answer : 
The biological agent which are used to control weeds, insects and pathogen are called biopesticides.
The micro-organisms that are used as biopesticides are some viruses, bacteria, fungi and their products.
The bacterium Bacillus thuringiensis was the first biopesticide to be used on commercial scale. 

Question. Some microbes act as biofertilisers. Explain with the help of three suitable examples.
Answer : 
(i) Rhizobium : Symbiotically fix atmospheric nitrogen into organic forms which can be used by the plant as nutrients.
(ii) Azospirullum / Azotobacter : Free living bacteria fix atmospheric nitrogen.
(iii) Glomus / Fungi : Symbiotic with plants absorbs phosphorus from soil and passes it to plant.
(iv) Cyanobacteria / Anabaena / Nostoc / Oscillatoria: Fix atmospheric nitrogen in aquatic and terrestrial environment.
(v) Blue green algae : Add organic matter to soil and increase soil fertility.

Question. Microbes can be used to decrease the use of chemical fertilizers. Explain how this can be accomplished. 
Answer :
 (a) Rhizobium bacteria present in the root nodules of leguminous plants forms a symbiotic association and fixes atmospheric nitrogen into organic forms, which is used by the plant as nutrient.
(b) Free-living bacteria in the soil Azospirillum and Azotobacter can fix atmospheric nitrogen, thus enriching the nitrogen content of the soil.
(c) Many members of the genus Glomus (Fungi) form mycorrhizal symbiotic associations with higher plants, in these the fungal symbiont absorbs phosphorus from soil and passes it to the plant.
(d) Cyanobacteria like Anabaena, Nostoc, Oscillatoria are autotrophic microbes widely distributed in aquatic and terrestrial environments, which can fix atmospheric nitrogen, also add organic matter to the soil and increase its fertility.