Unit A Reproduction

11. Rotate the high-power lens into place, and
locate one cell that is dividing. Determine which
stage of mitosis it is in. Copy Table 1 into your
notebook to record which of the four mitotic
stages the cell is in.
Table 1
Percentage of
Stage Number of cells cells in stage (%)
prophase
metaphase
anaphase
telophase
12. Move your slide, and repeat step 11 until you
have recorded information for 20 dividing cells.
Make sure that you do not include any cells in
interphase.
13. For each stage, use the formula in step 4 to
calculate the percentage of cells, and record
the values in your table.
14. Repeat steps 9 to 13 using the whitefish embryo
slide.
15. Calculate the length of time that cells spend in
each stage of mitosis. It usually takes between
12 and 16 hours to complete mitosis. You will
use 12 hours to make the calculations easier.
To calculate the number of hours spent in
each stage, multiply the percentage of cells by
12 hours. For example, suppose that you found
40 % of the 20 cells in metaphase:
Time spent in metaphase 40 % 12 h 4.8 h
16. Draw two circles to represent two clocks: one for
the onion root tip cells and one for the whitefish
embryo cells.
17. Use the data you collected to create clocks that
indicate the amount of time spent in each stage
of mitosis.
Analysis
(a) Which areas of the onion root tip have the
greatest amount of cell division?
(b) Were there any differences in the rates in the
three areas of the whitefish embryo? What do
you conclude from this?
(c) Which has the greater percentage of dividing
cells, the onion root tip or the whitefish embryo?
(d) Do your results support your hypothesis?
(e) Was your prediction correct? Explain.
(f) What do your clocks indicate about the time
spent in the different stages of mitosis in the
plant and the animal cell samples?
Evaluation
(g) Describe possible sources of error in this
investigation.
(h) How could you improve the procedure for this
investigation?
(i) Are there stages missing from your cell clock?
If so, identify them.
Synthesis
(j) What is the benefit of knowing the rate of cell
division in various organisms?
(k) Describe a different method that you could use
to calculate the rate of growth in living things.
(l) Although mitosis is divided into stages to make
it easier to discuss, the process is continuous.
Which of your observations suggest that mitosis
is a continuous process?
(m) Choose one of the cell division rates you
determined in this investigation. Draw a circle
graph that shows the percentages of cells
dividing and not dividing.
(n) Technology allows scientists to count cells much
faster than you did in this investigation. Suggest
a method for counting cells using technology.
LEARNING TIP
A clock is a type of circle (or pie) graph. Refer to the Skills Handbook
for help constructing a circle graph.
NEL
Chapter 2 Investigation 67