You take a sample of bacteria with DNA that contains only 14N and allow these cells to replicate in a medium that contains only 15N. After 3 rounds of replication, what percent of the DNA molecules will contain one strand with only 14N and one strand with only 15N?

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area