Examples of free-living bacteria that fix atmospheric nitrogen in the soil, enriching its nitrogen content, include:

[Microbes-in-Human-Welfare] [class-xii ]

• Lactobacillus and Streptococcus
• Azospirillum and Azotobacter
• Methanobacterium and Clostridium
• Penicillium and Trichoderma
Correct Option: B  [ Azospirillum and Azotobacter ]

Remark: Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter).

The symbiotic association formed between fungi and plants is known as:

[Microbes-in-Human-Welfare] [class-xii ]

• Nitrogen fixation
• Fermentation
• Mycorrhiza
• Biocontrol
Correct Option: C  [ Mycorrhiza ]

Remark: Fungi are also known to form symbiotic associations with plants (mycorrhiza).

Many members of the genus *Glomus* form which type of association?

[Microbes-in-Human-Welfare] [class-xii ]

• Anaerobic sludge digesters
• Lactic acid cultures
• Mycorrhiza
• Baculovirus hosts
Correct Option: C  [ Mycorrhiza ]

Remark: Many members of the genus Glomus form mycorrhiza.

Plants having mycorrhizal associations derive benefits such as resistance to root-borne pathogens and tolerance to:

[Microbes-in-Human-Welfare] [class-xii ]

• Low humidity
• Salinity and drought
• High light intensity
• Acidic soil pH
Correct Option: B  [ Salinity and drought ]

Remark: Plants having such associations show benefits such as resistance to root-borne pathogens, tolerance to salinity and drought.

Cyanobacteria are autotrophic microbes that are widely distributed in aquatic and terrestrial environments and many can fix:

[Microbes-in-Human-Welfare] [class-xii ]

• Atmospheric oxygen
• Soil carbon
• Atmospheric nitrogen
• Atmospheric sulfur
Correct Option: C  [ Atmospheric nitrogen ]

Remark: Cyanobacteria are autotrophic microbes... many of which can fix atmospheric nitrogen.

Examples of cyanobacteria that function as important biofertilisers, especially in paddy fields, include:

[Microbes-in-Human-Welfare] [class-xii ]

• Methanobacterium and Azotobacter
• Anabaena, Nostoc, and Oscillatoria
• Glomus and Trichoderma
• Lactobacillus and Streptococcus
Correct Option: B  [ Anabaena, Nostoc, and Oscillatoria ]

Remark: e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser.

Besides N2 fixation, Blue green algae (Cyanobacteria) also contribute to soil fertility by adding:

[Microbes-in-Human-Welfare] [class-xii ]

• Chemical fertilizers
• Organic matter
• Pesticides
• Weedicides
Correct Option: B  [ Organic matter ]

Remark: Blue green algae also add organic matter to the soil and increase its fertility.

What essential component is added to milk by LAB that helps in the coagulation and partial digestion of milk proteins?

[Microbes-in-Human-Welfare] [class-xii ]

• Enzymes
• Acids
• Antibiotics
• Fungal filaments
Correct Option: B  [ Acids ]

Remark: During growth, the LAB produce acids that coagulate and partially digest the milk proteins.

A small amount of curd added to fresh milk to initiate curd formation is known as:

[Microbes-in-Human-Welfare] [class-xii ]

• A colony
• A fermentor
• Inoculum or starter
• Slurry
Correct Option: C  [ Inoculum or starter ]

Remark: A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB.

Which disease mentioned in the text used to be treated extensively with Penicillin, especially for wounded soldiers during World War II?

[Microbes-in-Human-Welfare] [class-xii ]

• Malaria
• Tuberculosis
• Infections resulting from wounds
• Cholera
Correct Option: C  [ Infections resulting from wounds ]

Remark: This antibiotic [Penicillin] was extensively used to treat American soldiers wounded in World War II.