Final answer:
The difference in length between the two longest bands in the DNA ladder is 3099 base pairs.
Step-by-step explanation:
The DNA ladder contains bands of different base-pair lengths, including 6751, 3652, 2827, 1568, 1118, 825, and 630 base pairs. To find the difference in length between the two longest bands, we can subtract the length of the second longest band from the length of the longest band. The two longest bands in this case are 6751 base pairs and 3652 base pairs. Subtracting the length of the second longest band from the length of the longest band gives us a difference of 6751 - 3652 = 3099 base pairs.