Answer: 1. Determine the number of doubling periods: - The bacteria double every 4 hours, and the experiment runs for 12 hours.- Number of doubling periods = 12 hours / 4 hours/period = 3 periods 2. Calculate the bacteria population after each doubling period: - Start: 200 bacteria- After 1 period (4 hours): 200 bacteria * 2 = 400 bacteria- After 2 periods (8 hours): 400 bacteria * 2 = 800 bacteria- After 3 periods (12 hours): 800 bacteria * 2 = 1600 bacteria Answer: There will be 1600 bacteria present at the end of the 12th hour.