Unit A Reproduction

2B
Investigation
Determining the Rate of
Cell Division in Plant and
Animal Cells
An understanding of why and how cells undergo cell
division is important to many fields of science. One
of these fields is agriculture. A great deal of money is
spent on chemicals to increase plant growth. Scientists
can calculate the efficiency of these chemicals by
studying rates of cell division.
Question
Can you tell how fast an organism is growing by
looking at its cells?
Hypothesis
Write a hypothesis about how you can tell the rate
at which an organism is growing by observing
prepared slides.
Prediction
Predict what you will observe in the cells of an
organism when it is growing.
Experimental Design
In Investigation 2A, you observed cell division and
compared the process of mitosis in plant and animal
cells. In Part 1 of this investigation, you will examine
prepared slides of plant and animal cells under a
microscope and determine the percentage of cells that
are dividing. In Part 2, you will determine the rate of
cell division by making a cell-division clock.
Materials
• microscope
• prepared slide of an onion root tip
• prepared slide of a whitefish embryo
LEARNING TIP
If you need to review how to write a hypothesis, refer to Chapter 1.
INQUIRY SKILLS
Questioning
Hypothesizing
Predicting
Planning
Procedure
Conducting
Recording
Analyzing
Evaluating
Synthesizing
Communicating
Part 1: Determining the Percentage of Cells
That Are Dividing
1. Focus the onion root tip slide under the
low-power lens using the coarse-adjustment
knob. Locate dividing cells, and centre them
in the field of view.
2. Rotate the medium-power lens into place.
Focus and centre the dividing cells.
3. Notice that the cells form lines that are roughly
parallel to one another. Choose a line of cells
with many cells in various stages of mitosis.
Count 20 cells. Record the number of cells, in
these 20 cells, that are in mitosis.
4. Calculate the percentage of cells that are dividing.
For example, if you counted 10 cells dividing,
you would calculate the percentage as follows:
Percentage of cells dividing 10 100 % 50 %
20
5. Repeat steps 3 and 4 for two other lines of
20 onion cells. Record your results in a table.
6. Rotate the low-power lens into place, and
remove the slide from the stage.
7. Predict whether the onion root tip or the
whitefish embryo will have a greater percentage
of dividing cells. Record your prediction, and
give reasons for it.
8. Repeat steps 1 to 5 using the whitefish embryo, but
instead of looking for a line of dividing cells, look
for an area of dividing cells.
Part 2: Designing a Cell Division Clock
9. Focus the onion root tip under the low-power
lens using the coarse-adjustment knob. Locate
dividing cells, and centre them in the field of view.
10. Rotate the medium-power lens into place. Focus
and centre the dividing cells.
66 Unit A Reproduction
NEL