Scientists investigated DNA replication by repeating the experiments of Meselson and Stahl. They grew bacteria for several generations in a nutrient solution containing a heavy form of nitrogen (15N). The bacteria integrated the heavy nitrogen into their DNA as part of the DNA replication process. DNA was then isolated from a sample of these bacterial cells. The scientists then transferred some of the bacteria (grown in 15N) to a nutrient solution containing the lighter form of nitrogen (14N). The bacteria were allowed to grow and divide. After growth of one cell division in the 1"N medium, DNA was isolated from a sample of these bacteria. A further sample of DNA was then obtained from cells grown for two further divisions in the 14N medium. The DNA samples from the bacteria grown in 15N and 14N were transferred to separate tubes, and suspended in a solution of sucrose. These tubes were centrifuged (spun) at the same speed and for the same length of time, and different bands of DNA settled at different places in each tube. Figure 1 below shows an example of the scientists' results. Figure 1 Band containing DNA from the sample of bacteria Solution Sample 1 Bacteria grown for several generations in a nutrient solufion containing 1N Sample 2 Bacteria grown in a nutent solution containing "N for one oell division Sample 3 Bacteria grown in a nutrient solution contsining N for two cell divisions a) Table 1 below shows the types of DNA molecule (A, B and C) that could be present in samples 1, 2 and 3 above. Table 1 Type(s) of DNA molecule present in each sample 15N 15N 15N 14N 14N 14N Sample A B C 1 2 3.