Answer: B. Plasmids are small, circular DNA molecules that can be transferred between bacteria.
Explanation: Plasmids are not carbohydrates, they are small, circular DNA molecules that can be found in bacteria. They are not part of the bacterial chromosome, but they can replicate independently of the chromosome. Plasmids can carry genes for a variety of traits, including antibiotic resistance, the ability to produce toxins, and the ability to break down certain types of plastic.
The observation that the E. coli bacteria gained the ability to break down plastic after plasmid transfer from the bacteria with the ability to break down plastic suggests that the plasmid contained the gene for this trait. This is further supported by the fact that plasmids are known to be able to transfer between bacteria.
So, the inference that can be drawn about the nature of plasmids from this observation is that they are small, circular DNA molecules that can be transferred between bacteria and carry genes for a variety of traits.
The other options are incorrect. Option A is incorrect because plasmids are not carbohydrates. Option C is incorrect because plasmids are not essential for bacterial survival. Option D is incorrect because plasmids can carry genes for a variety of traits, not just antibiotic resistance. Option E is incorrect because plasmids are not always transferred between bacteria.