Organic Pollutants and Persistence Questions and Answers

Q: How bioavailability of recalcitrant hydrocarbons is increased through microbial interaction with smaller solubilized/pseudosolubilized hydrocarbon droplets ?

Bioavailability is increased by secretion of biosurfactants.Hydrocarbons such as alkanes and polycyclic aromatics dissolve poorly in water, so microbes cannot take them up readily. Many degraders secrete biosurfactants, such as rhamnolipids, which emulsify the oil into fine droplets and draw hydrocarbon molecules into micelles (pseudosolubilisation). The cells can then take up the hydrocarbon from these small solubilized droplets.Chemotaxis moves cells towards a substance but does not make it more available. Efflux pumps export toxic compounds out of the cell. An altered, more hydrophobic cell surface lets cells attach directly to large oil drops, a different mechanism from uptake through solubilized droplets.

Q: The continuous increase in concentration of a toxicant at successive trophic levels in a food chain is :

The process is biomagnification.A persistent, fat-soluble toxicant such as DDT or methylmercury is not broken down or excreted easily. Each consumer eats many organisms from the level below and retains what they contained, so the concentration rises at every step up the food chain. Fish-eating birds at the top of the chain carried DDT residues millions of times higher than in the water, which thinned their eggshells.Bioremediation is the use of organisms to clean up pollutants. Biotransformation is the chemical change of a substance inside an organism. Bioaugmentation is adding selected microbes to speed up the breakdown of a contaminant. None describes a build-up along the food chain.

Q: 'Superbug' was a term coined for micro-organism engineered for :

The superbug was engineered for hydrocarbon degradation.Ananda Mohan Chakrabarty at General Electric combined plasmids from several Pseudomonas strains into one bacterium able to break down several components of crude oil. It was proposed for cleaning oil spills, and the 1980 US Supreme Court case Diamond v. Chakrabarty made it the first living organism to be patented. The press called it the 'superbug'.The term was not coined for antibiotic, probiotic or insulin-producing microbes. Today 'superbug' is also used loosely for antibiotic-resistant bacteria, which is the trap in option A, but that is a later, different usage.

Q: Which one of the following is incorrect about POPs ?

The incorrect pairing is Aldrin - to control fungi.Aldrin is an organochlorine insecticide. It was used against soil insects such as termites and rootworms, not as a fungicide, and it is one of the original twelve POPs under the Stockholm Convention.The other pairings are correct: endosulfan was used against crop pests, DDT against mosquitoes and other disease vectors, and chlordane against termites.

Q: LD50 refers to ...........

LD50 is the dose at which 50% of all test animals die.LD stands for lethal dose. LD50 is the dose, usually in mg of substance per kg of body weight, that kills half of a test population within a set period. It is the standard measure of acute toxicity: the lower the LD50, the more toxic the substance.The dose at which 50% of the animals show a specified response, short of death, is the ED50 (effective dose). The dose that kills all the animals is the LD100. The lowest dose that kills any animal is the LDLo (lowest lethal dose). Each is a different point on the dose-response curve.

How bioavailability of recalcitrant hydrocarbons is increased through microbial interaction with smaller solubilized/pseudosolubilized hydrocarbon droplets ?

A.Secretion of biosurfactants
B.Chemotaxis
C.Efflux pumps
D.Altered cell surface property

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: A

Bioavailability is increased by secretion of biosurfactants.

Hydrocarbons such as alkanes and polycyclic aromatics dissolve poorly in water, so microbes cannot take them up readily. Many degraders secrete biosurfactants, such as rhamnolipids, which emulsify the oil into fine droplets and draw hydrocarbon molecules into micelles (pseudosolubilisation). The cells can then take up the hydrocarbon from these small solubilized droplets.

Chemotaxis moves cells towards a substance but does not make it more available. Efflux pumps export toxic compounds out of the cell. An altered, more hydrophobic cell surface lets cells attach directly to large oil drops, a different mechanism from uptake through solubilized droplets.

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The continuous increase in concentration of a toxicant at successive trophic levels in a food chain is :

A.Bioremediation
B.Biotransformation
C.Bioaugmentation
D.Biomagnification

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The process is biomagnification.

A persistent, fat-soluble toxicant such as DDT or methylmercury is not broken down or excreted easily. Each consumer eats many organisms from the level below and retains what they contained, so the concentration rises at every step up the food chain. Fish-eating birds at the top of the chain carried DDT residues millions of times higher than in the water, which thinned their eggshells.

Bioremediation is the use of organisms to clean up pollutants. Biotransformation is the chemical change of a substance inside an organism. Bioaugmentation is adding selected microbes to speed up the breakdown of a contaminant. None describes a build-up along the food chain.

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'Superbug' was a term coined for micro-organism engineered for :

A.Antibiotic production
B.Probiotic production
C.Hydrocarbon degradation
D.Insulin production

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: C

The superbug was engineered for hydrocarbon degradation.

Ananda Mohan Chakrabarty at General Electric combined plasmids from several Pseudomonas strains into one bacterium able to break down several components of crude oil. It was proposed for cleaning oil spills, and the 1980 US Supreme Court case Diamond v. Chakrabarty made it the first living organism to be patented. The press called it the 'superbug'.

The term was not coined for antibiotic, probiotic or insulin-producing microbes. Today 'superbug' is also used loosely for antibiotic-resistant bacteria, which is the trap in option A, but that is a later, different usage.

Discuss in Forum

Which one of the following is incorrect about POPs ?

A.Endosulfan - to control crop pests
B.DDT - to control disease vectors
C.Aldrin - to control fungi
D.Chlordane - to control termites

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: C

The incorrect pairing is Aldrin - to control fungi.

Aldrin is an organochlorine insecticide. It was used against soil insects such as termites and rootworms, not as a fungicide, and it is one of the original twelve POPs under the Stockholm Convention.

The other pairings are correct: endosulfan was used against crop pests, DDT against mosquitoes and other disease vectors, and chlordane against termites.

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LD50 refers to ...........

A.The dose at which 50% of all test animals die
B.The dose at which 50% of the animals demonstrate a response to the chemicals
C.The dose at which all of the test animals die
D.The dose at which at least one of the test animals dies.

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: A

LD50 is the dose at which 50% of all test animals die.

LD stands for lethal dose. LD50 is the dose, usually in mg of substance per kg of body weight, that kills half of a test population within a set period. It is the standard measure of acute toxicity: the lower the LD50, the more toxic the substance.

The dose at which 50% of the animals show a specified response, short of death, is the ED50 (effective dose). The dose that kills all the animals is the LD100. The lowest dose that kills any animal is the LDLo (lowest lethal dose). Each is a different point on the dose-response curve.

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