What happens to bacterial cells during the active stage of growth?

• A. They form endospores in adverse conditions.
• B. Phagocytosis by immune cells.
• C. Complete dormancy with no reproduction.
• D. Mitosis or binary fission: Bacteria reproduce and grow rapidly.

Answer: (D)

Active growth means bacteria are rapidly dividing and increasing in number. In prokaryotes, reproduction happens by binary fission, where the DNA is replicated, the cell enlarges, and a septum splits the cell into two identical daughter cells. This drives exponential population growth, especially when nutrients are plentiful. Mitosis is a process of eukaryotic cells and does not occur in bacteria, which is why binary fission is the correct mechanism here. Endospore formation happens under stress, phagocytosis is a host defense mechanism, and complete dormancy with no reproduction would not describe the active growth phase. So the best description of the active stage is that bacteria reproduce and grow rapidly by binary fission.