Question

activity: onion cell division lab
student instructions
objective: observe the phases of mitosis in an onion root tip and identify
the time spent in each phase.
background:
you will be observing a slide that has preserved cells in a particular moment in time. by
identifying how many cells are in a particular phase of the cell cycle, youll be able to
estimate how long the cell spends in each phase. the cells you are observing are from an
onion root tip, which is exactly what it sounds like: the tip of an onions root. these tiny
sections of the roots grow rapidly.
instructions:

1. look at the onion root tip slides under the microscope on low power. increase the

power until you can see individual cells.

1. identify one of the cells that is in interphase. these cells have a round, bluish/purple

nucleus. the chromosomes are not coiled, so they are not visible as x shapes or thick
threads.
*hint: most of the cells will look like this!

1. position the slide so that on high power, your whole field of view is made of onion

cells. in other words, you shouldnt see any blank space.

1. next, systematically (row by row) observe each cell. for each cell, put a tally mark in

the table below based on the phase of the cell cycle that it is in. if it appears to be
between two of the phases, just pick one.

1. continue this tally method until youve counted and tallied every cell within your

field of view.

	interphase	prophase	metaphase	anaphase	telophase
% of total	90%	14%	2%	1.25%

1. once all the cells have been tallied, calculate the total number of cells in your field of

view by adding up all the tallies. put the total tally number here: 400

1. calculate the percentage of the total cells that are in each phase (ex:

#interphase/total cells) and record the number in the second row of the table above.

Explanation:

Step1: Find total cells

Sum the number of cells in each phase: \( 360 + 15 + 10 + 4 + 7 = 400 \).

Step2: Calculate percentage for Prophase

Use the formula \( \text{Percentage} = \frac{\text{Number of cells in phase}}{\text{Total cells}} \times 100 \). For Prophase: \( \frac{15}{400} \times 100 = 3.75\% \) (note: the handwritten 4% might be an error; correct calculation is shown here).

Step3: Calculate percentage for Metaphase

For Metaphase: \( \frac{10}{400} \times 100 = 2.5\% \) (handwritten 2% might be an error).

Step4: Calculate percentage for Anaphase

For Anaphase: \( \frac{4}{400} \times 100 = 1\% \) (handwritten 1.25% might be an error).

Step5: Calculate percentage for Telophase

For Telophase: \( \frac{7}{400} \times 100 = 1.75\% \).

Answer:

Total cells: 400
Prophase %: \( 3.75\% \)
Metaphase %: \( 2.5\% \)
Anaphase %: \( 1\% \)
Telophase %: \( 1.75\% \)

(Note: The handwritten percentages in the table have calculation errors; the above are the correct values based on the number of cells and total cells.)