IMAT 2015 Q34 [Eukaryotic Cell Cycle]

The table shows some events of the normal eukaryotic cell cycle.

image

Which row shows the correct sequence of events (left to right) as they occur during part of this cell cycle?

A. row 5
B. row 2
C. row 1
D. row 4
E. row 3

The answer here is choice E.

Is there any shortcut here? Unfortunately not, you will need to be very familiar with the steps of mitosis in order to answer this question, where you will match up your knowledge of the phases of mitosis with the sequences that have been given to you in the table above. It can be useful to have a mnemonic for the phases of mitosis to get you in track when answering questions regarding mitosis. A suggestion would be: PMAT = People Must Answer Telephones. These signify the phases prophase → metaphase → anaphase → telophase.

Let us then rationalize why choice E or row 3 is correct:

  1. “Chromosomes line up at the equator”: This is a description associated with metaphase. In this phase, the spindle collects all the chromosomes, and are lined up at the middle of the cell, or the “equator”. In metaphase, the kinetochores of the chromosomes are attached to the microtubules from spindle poles on either sides of the cell.

  2. “Spindle fibers shorten”: This is a description associated with anaphase. After the chromosomes have been lined up at the equator, the sister chromatids need to be separated from each other. This is only possible if the spindle fibers shorten and pull each sister chromatid towards opposite poles of the cell.

  3. “Nuclear envelop reappears”: This is a description associated with telophase. Before dividing into 2 daughter cells, the individual cell will need to regenerate its normal structures, which includes the re-establishment of nuclear membranes and nucleoli. And because the nuclear envelope is reappearing, at this phase, the chromosomes will begin to decondense again.

  4. “Cytoplasm divides”: This is a description of the process called cytokinesis, which is the division of the cytoplasm near the end of mitosis, to yield two daughter cells. This process of cytokinesis can usually be found overlapping with the end of anaphase or telophase.

Thus, if you will be able to notice, the sequence follows the PMAT sequence, which further supports that choice E is the only correct answer.