Passage I
The mitotic index (MI) for a group of cells is calculated as follows:
MI = 
Figure 1 shows the average MI for onion root tip cells as a function of their distance from the root cap.
Five hundred mitotic onion root tip cells were examined. Figure 2 shows the number of cells in each of the 4 mitotic phases.
Figure 3 shows 4 onion root tip cells (Cells 1-4), each of. which is in 1 of the 4 mitotic phases. In Figure 3, each phase is shown once. However, the cells are not arranged in order of the phases of mitosis.
Figure 3 adapted from Peter H. Raven, Ray F. Evert, and Susan E. Eichhorn, Biology of Plants, 4th ed. @1986 by Worth Publishers, Inc.
3. Based on Figure 2, of the onion root tip cells that were in mitosis, the proportion that were in prophase is closest to which of the following?
Your Answer is
Correct Answer is D
Explanation
Looking at figure 2, the ordinate corresponding to prophase is about 305, but the total number of cells in mitosis is 305+25+45+125=500, so the proportion of prophase is 305/500