In terms of phenol degrading bacteria answer the question: What is meant by “recalcitrance”? (2 marks) Give an example. (4 marks)

**What is meant by “recalcitrance”? (2 marks)** Recalcitrance refers to the resistance of certain compounds, particularly organic pollutants, to biological degradation. In the context of phenol-degrading bacteria, recalcitrance implies that phenolic compounds can be persistently resistant to microbial breakdown, making them difficult for bacteria to metabolize and degrade effectively. This resistance often arises due to the structural complexity of the molecules, which can inhibit the activity of microbial enzymes. **Example of recalcitrance (4 marks)** An example of recalcitrance in phenol degradation is chlorinated phenols, such as 2,4-dichlorophenol (DCP). DCP is a derivative of phenol where chlorine atoms are substituted onto the aromatic ring. The presence of chlorine atoms significantly alters the chemical properties of the compound, making it more stable and less susceptible to biodegradation. Many phenol-degrading bacteria struggle to utilize chlorinated phenols as carbon sources due to the halogenation, which can hinder enzyme activity and metabolic pathways needed for degradation. As a result, DCP can accumulate in the environment, representing a challenge for bioremediation efforts.