5. A human cell passes through 4 phases called A, B, C and D, each phase lasting for
different lengths of time. At the end of D the cell returns to A to continue this cycle. In
an experiment, a static snapshot of 106 unsynchronized cells was taken, and it was
found that 300,000 cells were in phase A, 400,000 cells were in phase B, 200,000
were in phase C and the rest in phase D. If the total time spent by one cell in the four
phases is known to be 24 hours, which of the following statements is true?
a. The time spent in phase A is 5.2 hours.
b. The time spent in phase B is 9.6 hours.
c. The time spent in phase C is 3.8 hours.
d. The time spent in any one phase cannot be obtained from the given
information.
Cell Cycle Phase Duration Calculation: CSIR NET Solved Question
In unsynchronized cell populations, the proportion of cells in each phase reflects the relative time spent in that phase during the cell cycle. For this CSIR NET Life Sciences question, analysis of the given snapshot reveals the correct option among the choices provided.
Problem Breakdown
A total of 1,000,000 cells show 300,000 in phase A, 400,000 in B, 200,000 in C, and 100,000 in D. Total cycle time equals 24 hours. The standard formula applies: time in phase = (cells in phase / total cells) × total cycle time.
-
Phase A: (300,000/1,000,000) × 24 = 7.2 hours
-
Phase B: (400,000/1,000,000) × 24 = 9.6 hours
-
Phase C: (200,000/1,000,000) × 24 = 4.8 hours
-
Phase D: (100,000/1,000,000) × 24 = 2.4 hours
Option Analysis
Option a (5.2 hours for A): Incorrect, as calculation yields 7.2 hours, not matching the data.
Option b (9.6 hours for B): Correct, precisely matching (400,000/1,000,000) × 24 = 9.6 hours.
Option c (3.8 hours for C): Incorrect; actual value is 4.8 hours based on 200,000 cells.
Option d (Cannot be obtained): Incorrect, as proportions directly yield phase durations in steady-state unsynchronized populations.
Introduction to Cell Cycle Phase Duration Analysis
Cell cycle phases duration calculation from snapshot populations proves essential for CSIR NET Life Sciences preparation. In unsynchronized human cells totaling 10^6 with given phase counts and 24-hour cycle, proportions determine exact times spent in phases A, B, C, D.
Key Calculation Method
The proportion method leverages steady-state distribution: longer phases contain more cells. Formula: (phase cells / total) × cycle time yields precise durations for exam questions.
CSIR NET Question Solution
Detailed computation confirms phase B duration at 9.6 hours, making option b true. This approach applies universally to mitosis snapshots in competitive exams.
