Final Answer:
During natural transformation, small pieces of extracellular DNA are taken up by competent cells. A double-stranded piece of DNA, not necessarily circular, can be taken up by a cell.
Step-by-step explanation:
Natural transformation is a process by which bacteria take up extracellular DNA from their environment. In this phenomenon, bacterial cells that are in a competent state have the ability to take up small fragments of DNA from their surroundings. This extracellular DNA can be single-stranded or double-stranded and is not restricted to a circular form. The competent cells integrate this foreign DNA into their own genome through recombination processes, leading to genetic diversity among bacterial populations. This natural transformation mechanism plays a crucial role in bacterial evolution and adaptation to changing environmental conditions.