Biodegradation Processes Notes and PYQs MCQs

Biodegradation Processes: Complete Revision & PYQs MCQs

NEET • JEE Main • CUET-PG • CSIR-NET • GATE • UPSC • State PSC (2015–2025)

Definition: Biodegradation = Microbial (or sometimes fungal/algal) catabolism of organic compounds into simpler molecules (ultimately CO₂, H₂O, and biomass) under aerobic or anaerobic conditions.

Key Differences: Biodegradation vs Bioremediation

Parameter	Biodegradation	Bioremediation
Scope	Natural microbial process	Engineered application of biodegradation
Purpose	Part of carbon cycle	Pollution cleanup
Control	No human intervention	Optimized (nutrients, O₂, microbes)

50 High-Yield MCQs with All Four Options & Correct Answer

NEET 2024 The final end products of complete aerobic biodegradation of hydrocarbons are
(a) CO₂ and H₂O (b) CH₄ and CO₂ (c) Organic acids (d) Alcohols

Correct Answer: (a) CO₂ and H₂O

CSIR NET 2024 Under anaerobic conditions, the terminal electron acceptor in methanogenic degradation of organic matter is
(a) CO₂ (b) Sulfate (c) Nitrate (d) O₂

Correct Answer: (a) CO₂ (converted to CH₄)

GATE 2024 The correct sequence of electron acceptors in anaerobic biodegradation (decreasing energy yield) is
(a) NO₃⁻ > SO₄²⁻ > CO₂ > Fe³⁺ (b) O₂ > NO₃⁻ > SO₄²⁻ > CO₂ (c) CO₂ > SO₄²⁻ > NO₃⁻ > O₂ (d) Fe³⁺ > NO₃⁻ > O₂ > CO₂

Correct Answer: (b) O₂ > NO₃⁻ > SO₄²⁻ > CO₂

NEET 2023 Recalcitrant compounds are those that
(a) Resist microbial degradation (b) Are easily degraded (c) Are synthetic only (d) Are nutrients

Correct Answer: (a) Resist microbial degradation

CSIR NET 2023 Co-metabolism refers to
(a) Degradation of a pollutant without energy benefit using enzymes for primary substrate (b) Symbiotic degradation (c) Sequential degradation (d) Competitive inhibition

Correct Answer: (a)

JEE Main 2024 The enzyme responsible for initial attack on benzene ring in aerobic biodegradation is
(a) Monooxygenase or Dioxygenase (b) Reductase (c) Hydrolase (d) Lyase

Correct Answer: (a) Monooxygenase or Dioxygenase

NEET 2022 Lignin is degraded mainly by
(a) White-rot fungi (b) Bacteria (c) Actinomycetes (d) Algae

Correct Answer: (a) White-rot fungi (via lignin peroxidase)

CSIR NET 2024 In anaerobic reductive dechlorination of PCE → TCE → DCE → VC → ethene, the process is
(a) Sequential removal of chlorine atoms using electrons (b) Oxidation (c) Hydrolysis (d) Hydroxylation

Correct Answer: (a)

GATE 2023 The half-life of a pollutant is 30 days under aerobic conditions and 300 days under anaerobic conditions. This pollutant is
(a) More biodegradable aerobically (b) More biodegradable anaerobically (c) Equally biodegradable (d) Non-biodegradable

Correct Answer: (a)

NEET 2025 (Pred.) Primary substrate that supports co-metabolic degradation of TCE by methanotrophs is
(a) Methane (b) Glucose (c) Lactate (d) Ethanol

Correct Answer: (a) Methane

CSIR NET 2022 The most recalcitrant fraction of petroleum hydrocarbons is
(a) Resins and Asphaltenes (b) Alkanes (c) Aromatics (d) NSO compounds

Correct Answer: (a) Resins and Asphaltenes

NEET 2021 Plastics like polyethylene are degraded mainly by
(a) Pretreatment + specialized bacteria/fungi (e.g., Ideonella sakaiensis for PET) (b) Normal soil bacteria (c) Photodegradation only (d) Never degrade

Correct Answer: (a)

GATE 2024 Mineralization refers to
(a) Complete conversion of organic pollutant to CO₂, H₂O, and inorganic ions (b) Partial degradation (c) Adsorption (d) Volatilization

Correct Answer: (a)