Grade 12 : Biology | Microbes in Human Welfare

Question 1

A dairy technician prepares curd by adding a starter inoculum of lactic acid bacteria (LAB) to lukewarm milk kept at optimum incubation temperature.

Which nutritional enhancement and physiological benefit are directly conferred by LAB during this conversion?

Accepted Answer

C) Enriches curd with Vitamin $	ext{B}_{12}$ and checks disease-causing microbes in the stomach

Answer

A) Decreases curd acidity and enhances Vitamin D concentration

Answer

B) Synthesizes large amounts of Vitamin C and degrades lactose to starch

Answer

D) Increases calcium bioavailability by solubilizing casein into free phosphorus

Question 2

The puffed-up appearance of dough used for preparing traditional foods like dosa and idli is primarily caused by:

Accepted Answer

B) Production and release of $	ext{CO}_2$ gas during microbial fermentation

Answer

A) Rapid cellular division of aerobic nitrifying bacteria

Answer

C) Hydrolysis of starch into glucose crystals under warm conditions

Answer

D) Accumulation of ethanol vapors inside sealed dough containers

Question 3

Large holes observed in 'Swiss cheese' develop due to high $ ext{CO}_2$ production by which specific bacterium?

Accepted Answer

A) Propionibacterium sharmanii

Answer

B) Penicillium roqueforti

Answer

C) Streptococcus thermophilus

Answer

D) Lactobacillus acidophilus

Question 4

A clinical biochemist isolates an enzyme from a microbial culture that functions as a 'clot buster' to clear intravascular thrombi in myocardial infarction patients.

Identify the therapeutic biomolecule and its microbial source:

Accepted Answer

D) Streptokinase from Streptococcus

Answer

A) Cyclosporin A from Trichoderma polysporum

Answer

B) Statin from Monascus purpureus

Answer

C) Pectinase from Aspergillus niger

Question 5

Assertion (A): Statins obtained from Monascus purpureus are prescribed to lower blood cholesterol levels.
Reason (R): Statins act as competitive inhibitors of the enzyme responsible for cholesterol synthesis.

Select the correct choice from the standard options:

Accepted Answer

A) Both (A) and (R) are true, and (R) is the correct explanation of (A).

Answer

B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).

Answer

C) (A) is true, but (R) is false.

Answer

D) (A) is false, but (R) is true.

Question 6

Cyclosporin A, an important bioactive immunosuppressive drug given to organ-transplant patients, is commercially extracted from:

Accepted Answer

C) Trichoderma polysporum

Answer

A) Acetobacter aceti

Answer

B) Clostridium butylicum

Answer

D) Saccharomyces cerevisiae

Question 7

Match the following organic acids with their producing microbial species correctly:

Organic Acid	Microorganism
1. Citric acid	p. Acetobacter aceti
2. Acetic acid	q. Clostridium butylicum
3. Butyric acid	r. Aspergillus niger

The correct combination is:

Accepted Answer

B) 1-r, 2-p, 3-q

Answer

A) 1-p, 2-q, 3-r

Answer

C) 1-q, 2-p, 3-r

Answer

D) 1-r, 2-q, 3-p

Question 8

During secondary sewage treatment, wastewater is pumped into massive aeration tanks where it is constantly agitated mechanically and air is pumped into it.

What happens to the Biochemical Oxygen Demand (BOD) during this stage?

Accepted Answer

D) BOD decreases significantly as flocs consume the major fraction of organic matter

Answer

A) BOD remains unaffected because microbes do not consume organic matter

Answer

B) BOD sharply increases as aerobic bacterial flocs reproduce exponentially

Answer

C) BOD stabilizes to zero instantaneously before secondary settling occurs

Question 9

The term 'flocs' in sewage wastewater treatment specifically refers to:

Accepted Answer

B) Masses of bacteria associated with fungal filaments forming mesh-like structures

Answer

A) Heavy inorganic grits settled during primary sedimentation

Answer

C) Anaerobic methane-producing bacterial pellets floating in primary clarifiers

Answer

D) Non-biodegradable synthetic polymers that coagulate suspended particles

Question 10

Assertion (A): A low value of BOD indicates high water pollution.
Reason (R): BOD measures the rate of uptake of oxygen by microorganisms in a water sample.

Choose the correct option:

Accepted Answer

A) (A) is false, but (R) is true.

Answer

B) (A) is true, but (R) is false.

Answer

C) Both (A) and (R) are true, and (R) is the correct explanation of (A).

Answer

D) Both (A) and (R) are false.

Question 11

In an anaerobic sludge digester at a municipal wastewater plant, anaerobic microbes digest the organic biomass and microbial flocs pumped from secondary settling tanks.

Which mixture of gases constitutes the biogas produced during this anaerobic digestion?

Accepted Answer

C) $	ext{CH}_4, 	ext{H}_2	ext{S}, 	ext{and } 	ext{CO}_2$

Answer

A) $	ext{CO}_2, 	ext{SO}_2, 	ext{and } 	ext{N}_2$

Answer

B) $	ext{CH}_4, 	ext{O}_2, 	ext{and } 	ext{CO}$

Answer

D) $	ext{NH}_3, 	ext{H}_2	ext{O}, 	ext{and } 	ext{Cl}_2$

Question 12

Methanogens such as Methanobacterium are obligate/facultative anaerobes commonly found in:

Accepted Answer

D) Anaerobic sludge of STPs and the rumen of cattle

Answer

A) Aerobic trickling filters and surface ocean water

Answer

B) Chlorinated distribution systems and treated effluent

Answer

C) Root nodules of leguminous plants alongside Rhizobium

Question 13

Which traditional biocontrol agent is widely used to control aphids and mosquitoes respectively?

Accepted Answer

A) Ladybird beetles control aphids, while Dragonflies control mosquitoes

Answer

B) Dragonflies control aphids, while Ladybird beetles control mosquitoes

Answer

C) Trichoderma controls aphids, while Bacillus controls mosquitoes

Answer

D) Baculoviruses control aphids, while Glomus controls mosquitoes

Question 14

A farmer sprays dried spores of Bacillus thuringiensis suspended in water onto Brassica seedlings suffering from caterpillar infestation.

What happens when insect larvae ingest these bacterial spores?

Accepted Answer

B) Protoxin crystals solubilize in the alkaline gut, creating pores in epithelial cells

Answer

A) The spores block the respiratory spiracles, suffocating the larvae

Answer

C) The bacteria secrete neurotoxins that irreversibly inhibit neuromuscular synapses

Answer

D) Fungal hyphae proliferate inside the hemolymph and absorb insect fluids

Question 15

Baculoviruses belonging to the genus Nucleopolyhedrovirus are excellent candidates for biological control because they are:

Accepted Answer

C) Species-specific, narrow-spectrum insecticides with no negative impacts on non-target organisms

Answer

A) Broad-spectrum pathogens harmful to birds and mammals

Answer

B) Non-specific predators that eliminate entire insect populations

Answer

D) Symbiotic bacteria that enhance insect resistance to chemical pesticides

Question 16

Assertion (A): Mycorrhizal associations formed by the fungal genus Glomus benefit plants grown in phosphorus-deficient soils.
Reason (R): The fungal partner absorbs phosphorus from the soil and translocates it to the host plant.

Select the correct choice:

Accepted Answer

B) Both (A) and (R) are true, and (R) is the correct explanation of (A).

Answer

A) Both (A) and (R) are true, but (R) is not the correct explanation of (A).

Answer

C) (A) is true, but (R) is false.

Answer

D) (A) is false, but (R) is true.

Question 17

Which of the following is a free-living soil bacterium capable of fixing atmospheric nitrogen non-symbiotically?

Accepted Answer

D) Azotobacter

Answer

A) Rhizobium

Answer

B) Frankia

Answer

C) Anabaena azollae

Question 18

Paddy crop farmers often cultivate a small aquatic water fern on flooded terraces to enhance nitrogen availability without applying urea.

Which cyanobacterial symbiont living within the fronds of Azolla acts as this potent biofertilizer?

Accepted Answer

A) Anabaena azollae

Answer

B) Nostoc commune

Answer

C) Spirulina maxima

Answer

D) Oscillatoria

Question 19

Bottled fruit juices purchased from retail markets are noticeably clearer and less turbid than fresh homemade juices because commercial juices are clarified using:

Accepted Answer

C) Pectinases and proteases

Answer

A) Amylases and cellulases

Answer

B) Lipases and streptokinase

Answer

D) Ligases and endonucleases

Question 20

Which free-living soil fungus is extensively deployed as an effective biocontrol agent against multiple soil-borne plant root pathogens?

Accepted Answer

D) Trichoderma viride

Answer

A) Penicillium notatum

Answer

B) Aspergillus niger

Answer

C) Rhizopus stolonifer

Set 5Grade 12 : Biology | Microbes in Human Welfare