Final answer:
The dense film laid down by many prokaryotes is known as a biofilm. Biofilms are complex microbial communities that provide enhanced protection and resistance to sterilization methods.
Step-by-step explanation:
The Dense Film Laid Down by Many Prokaryotes
The answer to the student's question is c. Biofilms. Biofilms are dense films formed by prokaryotes and are essential to their ecology. Most prokaryotes prefer living in communities, making these structures common. A biofilm is a complex aggregation of microorganisms marked by cells that are adhered to a surface and enmeshed in a self-produced extracellular polymeric matrix composed of polysaccharides, proteins, and nucleic acids. This protective matrix, also known as exopolysaccharidic (EPS), enhances the robustness of the community and provides resistance to common sterilization methods, including antibiotics and disinfectants, which makes them difficult to destroy.
Biofilms are not only composed of prokaryotes; fungal and mixed biofilms also exist, displaying the diverse nature of these microbial communities. Biofilms show a different kind of ecology than what was previously understood; they are not simply planktonic or isolated bacteria but structured communities that adhere to surfaces, including natural environments and the human body.