Question

A student examines a thin section of an onion-root tip and records the number of cells that are in each stage of the cell cycle. he observes 94 cells in interphase, 14 cells in prophase, 3 cells in prometaphase, 3 cells in metaphase, 5 cells in anaphase and 1 cell in telophase. if the complete cell cycle in an onion-root tip requires 22 hours, what is the average duration in hour of anaphase in the cycle?

Answer 1

The answer is 0.92 hour, which is the average duration in an hour of anaphase in the cycle.

The information required to answer the problem is the average duration of each stage of the cell cycle.The numbers of cells in different stages of the cell cycle and the time required for a complete cell is the information that should be provided in order to solve the problem. 

The problem is solved in two steps. In which first is to calculate the proportions of cells in each stage of the cell cycle, which correspond to the amount of time that an average cell spends in each stage. For example, if cells spend 90% of their time in interphase, then at any given moment, 90% of the cells will be in interphase. The second step is to convert the proportions into lengths of time which are completed by multiplying the proportions by the total time of the cell cycle (22 hours).

1. Calculate the proportion of cells at each stage. The proportion of cells at each stage is equal to the number of cells found in that stage divided by the total number of cells observed. Note that the total of all the proportions should equal 1.0. 

• Interphase 94/120 = 0.783
• Prophase 14/120 = 0.117
• Prometaphase 3/120 = 0.025
• Metaphase 3/120 = 0.025
• Anaphase 5/120 = 0.042
• Telophase 1/120 = 0.008

Check the calculations by making sure that the proportions sum to 1.0

2. Determine the average duration of each stage. Note that the total time for all stages should equal 22 hours. To determine the average duration of each stage, multiply the proportion of cells in each stage by the time required for the entire cell cycle.

• Interphase 0.783 × 22 hours = 17.23 hours
• Prophase 0.117 × 22 hours = 2.57 hours
• Prometaphase 0.025 × 22 hours = 0.55 hour
• Metaphase 0.025 × 22 hours = 0.55 hour
• Anaphase 0.042 × 22 hours = 0.92 hour
• Telophase 0.008 × 22 hours = 0.18 hour