This biology question covers important biological concepts and processes. The step-by-step explanation below helps you understand the underlying mechanisms and reasoning.
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1. Distinguish between Biodegradation and Bioremediation (5 marks) Biodegradation refers to the natural process by which microorganisms (bacteria, fungi, etc.) break down complex organic compounds into simpler substances like CO_2, H_2O, minerals, and biomass. Bioremediation is the deliberate application of biodegradation using microorganisms (or plants/animals) to clean up or neutralize pollutants and contaminants in the environment, such as oil spills or heavy metals in soil/water. Key differences: | Aspect | Biodegradation | Bioremediation | |--------|----------------|---------------| | Definition | Natural microbial breakdown of organics | Engineered use of microbes to remediate pollutants | | Scope | Any organic matter degradation | Targeted environmental cleanup | | Purpose | Part of nutrient cycling | Pollution control/restoration | | Control | Spontaneous | Engineered (bioaugmentation/biostimulation) | | Examples | Decay of leaves | Oil spill cleanup using bacteria | 2. Write short notes on: (i) Biofilm formation (3 marks) Biofilm formation is a multi-step process where microorganisms adhere to surfaces and develop structured communities embedded in a self-produced matrix of extracellular polymeric substances (EPS). Steps: Initial attachment: Reversible adhesion via weak forces (van der Waals, hydrophobic interactions). Irreversible attachment: Firm binding via pili, fimbriae, adhesins. Microcolony formation: EPS production (polysaccharides, proteins, DNA). Maturation: Mushroom-like 3D structure with channels for nutrient flow. Dispersion: Cells release to colonize new sites. Biofilms protect microbes from antibiotics, enhance resistance (e.g., dental plaque, medical device infections). (ii) Quorum sensing (2 marks) Quorum sensing (QS) is cell-to-cell communication in bacteria via autoinducer signaling molecules (e.g., acyl-homoserine lactones in Gram-negatives). Process: Low density: Low autoinducer. High density: Autoinducer threshold reached → gene expression (bioluminescence, virulence, biofilm). Examples: Vibrio fischeri (light), Pseudomonas aeruginosa (pathogenicity). Regulates population-dependent behaviors. 3. List and describe major compositional factors that influence biodegradation (2.5 marks) Major factors: Chemical structure: Straight-chain alkanes degrade faster than branched/aromatic; position of functional groups matters. Molecular weight: Low MW polymers degrade easier than high MW. Solubility/Hydrophobicity: Hydrophilic > hydrophobic (better microbial access). Functional groups: Presence of OH, COOH enhances via co-metabolism. Inhibitors: Halogens, heavy metals slow degradation. 4. Write short note on the mechanism by which metal ions regulate the oxidation of hydrocarbons and how they can [likely "inhibit/promote"] (5 marks) (Note: Assuming full question based on snippet "Write short note on the mechanism by which metal ions regulate the oxidation of hydrocarbons and how they can") Metal ions (e.g., Fe^2+, Mn^2+, Co^2+) act as cofactors in mono/dioxygenase enzymes for hydrocarbon oxidation. Mechanism: Activation: Fe^2+ in alkane hydroxylases (e.g., rubredoxin) facilitates O_2 insertion into C-H bonds. Electron transfer: Ions shuttle electrons in redox reactions. Cometabolism: Metals induce enzymes for co-substrates. Promotion: Essential for dioxygenases in aromatics (e.g., catechol dioxygenase). Inhibition: Excess Hg^2+, Cd^2+ denature enzymes, compete sites, generate ROS. 5. List types of synthetic biodegradable plastics and one microbial genus capable of their degradation (8.5 marks) Types of synthetic biodegradable plastics: Polylactic acid (PLA): From lactic acid; used in packaging. Degraded by Amycolatopsis sp. Polyhydroxyalkanoates (PHA): Bacterial polyesters (PHB, PHBV); films/bottles. Degraded by Pseudomonas sp. Polycaprolactone (PCL): Low MW polyester; drug delivery. Degraded by Bacillus sp. Polybutylene succinate (PBS): Aliphatic polyester; bags. Degraded by Rhodococcus sp. Polybutylene adipate terephthalate (PBAT): Flexible; mulch films. Degraded by Clostridium sp. Each has microbes producing extracellular depolymerases under aerobic/anaerobic conditions. 6. Using well labelled diagram, explain the mechanism of plastic biodegradation under aerobic conditions (17.5 marks) Mechanism of aerobic plastic biodegradation: Plastics (e.g., PE, PET, PU) are xenobiotics; microbes use them via extracellular/intracellular enzymes. Steps: Step 1: Biodeterioration - Surface colonization by microbes (biofilm), physical cracking via acids/enzymes. Step 2: Biofragmentation - Extracellular enzymes (e.g., PETase, MHETase for PET; laccases, peroxidases for PU/PE): End-chain attack → oligomers. Random scission → smaller fragments. Step 3: Bioassimilation - Oligomers transported via ABC transporters; intracellular oxidation: Alcohol/aldehyde dehydrogenases → carboxylic acids. -oxidation pathway → acetyl-CoA. Step 4: Mineralization - TCA cycle → CO_2, H_2O, biomass. Key enzymes (example for PET): PETase: PET → MHET + TPA. MHETase: MHET → TPA + EG. TPA/EG → central metabolism. Factors: O_2, neutral pH, 30-50°C optimal. Diagram (schematic pathway): &Plastic polymer (e.g., PET) \\ & (PETase, cutinase) \\ &Oligomers (MHET, TPA) \\ & (transporters) \\ &Intracellular: -oxidation Acetyl-CoA \\ & (TCA cycle) \\ &CO_2 + H_2O + biomass Microbes: Ideonella sakaiensis (PET), Pseudomonas (PE/PHA), Aspergillus (fungi for PU). **Final summary: Aerobic pathway ensures complete mineralization with O_2 as terminal electron acceptor.