Hands-On Lab
Observing Mitosis
Timing: one 90-minute class session
Objective(s):
In this activity, students will prepare slides of onion root tip cells and observe them under a
microscope. Students have the option to organize and present quantitative data using a
computer spreadsheet program. Students will then use their understanding of cell division to
identify the stages of mitosis.
Safety Precautions:
Remind students to wear gloves, aprons, goggles, and closed-toe shoes, and not to eat or drink
anything in the lab (including the experimental materials). Tell students to report any broken
glass and not to try and clean it up by themselves. Remind students to handle the toluidine blue
carefully so as not to stain clothing. Students should also be cautious when handling the
hydrochloric acid and the razor blade.
Materials:
Per class:
 onion
 glass jar (wide enough to fit the bottom of an onion)
 water
 toothpicks, 5
Per pair:
 cover slip
 distilled water, 2 mL
 forceps
 hydrochloric acid (1M), 2 mL
 compound microscope
 onion root tip
 pencil
 petri dish
 pipette
 razor blade
 scissors
 slide
 disposable gloves, one pair per student
 tissue or paper towel
 toluidine blue, 2 mL
 goggles, one pair per student
 lab apron, one per student
 clock with minute hand or stopwatch
 computer with spreadsheet software
Teacher Preparation:
Prepare the onion for this investigation by cutting off any old roots that appear brown or wilted.
Then place the onion so that only its root portion is underwater. This can be done by putting
toothpicks into the onion and using them to suspend the onion from the rim of a water-filled jar.
Allow the onion to remain in the water for 2–3 days. Remove the onion from the water before
the investigation. To save time, you may prepare the onion root tip slides for students by
following the procedure described in the Directed Inquiry. If the class is larger than 20 students,
more than one onion may be needed for this investigation. Prepare a copy of the Student
Investigation Sheet for each student.
Procedure:
The Hands-On Labs include both Directed and Guided Inquiry approaches. If your students are
new to the investigational methods being used in the Hands-On Lab, it is recommended that the
Directed Inquiry approach be used to provide scaffolding that will ensure student safety and
support the success of their investigations. Often, the Directed Inquiry approach involves
modeling the basic laboratory techniques and methods to be used in the activity. A discussion of
each step in the investigative process will also be included. In some cases, students may then
be asked to create a procedure based on the one modeled for them. This may involve changing
specific variables or adjusting the procedure to determine the effect on the outcome.
You may choose to use the Guided Inquiry path on its own or after completing the Directed
Inquiry activity. During Guided Inquiry, students are allowed to conduct the investigations more
independently. They will be given opportunities to formulate their own questions, develop their
own procedures, and/or manipulate variables of their own choosing. It may be necessary to
provide additional materials and supplies for students using Guided Inquiry. It will also be
important to set clear limits on students’ activities to ensure their safety and the relevance of
their inquiry experience to the content you are teaching.
Directed Inquiry
Have lab groups prepare slides of onion root tips using the following procedure. Demonstrate
each step for students before they attempt the procedure on their own. Remind students about
safety precautions, particularly when using the hydrochloric acid and razor blades.
1. Take a prepared onion. Cut off about 5 mm of the bottom of an onion root.
2. Place the root tip in a petri dish and use a pipette to add 1M HCl to the dish, covering
the root tip. Let the root tip sit for four minutes.
3. Use forceps to transfer the root tip to a clean microscope slide. Set the slide on a firm
surface such as the lab table and then use a razor blade to cut the root tip to about 1–2
mm. Throw away the remaining section of root tip.
4. Add two drops of toluidine blue stain to the root tip and let it sit for two minutes.
5. Absorb the excess stain by using a piece of tissue to blot around the root tip. Do not
touch the root tip itself.
6. Add a drop of water to the slide and place a cover slip on top of the root tip. Use the
eraser of a pencil to gently press straight down on the cover slip. Do not press hard
enough to break the coverslip. This will spread the cells into a single layer on the slide.
7. Observe the slide under a microscope to ensure that mitotic stages are visible. If the
cells are too close together to distinguish individual cells, remove the slide from the
microscope and gently press down on the cover slip again in order to spread the cells
more thinly.
8. Create a data table for each stage of mitosis. As a technology option use a
spreadsheet. Count the number of cells you observe at different stages of mitosis.
Record the data in a spreadsheet. Use the spreadsheet to calculate the percentage of
cells that are at each stage. Use the software to create a histogram of your data.
Once their slides have been prepared, instruct students to observe the chromosomes of the
cells closely under the microscope. Have students try to identify a cell in each stage of mitosis.
Guide them with the following questions:
 In what ways will the chromosomes appear different in each stage? For example, how
will the chromosomes appear in interphase versus prophase? Sample response: The
chromosomes in interphase will be difficult to observe and may look like one large dark
area in the nucleus. In prophase, they will be easier to see as chromatin begins to
condense.
Students should sketch their observations of each stage that they are able to identify, labeling
the structures that are visible. Also, have them create a data table like the one below to record
the average cell count for each stage. This will help them determine the relative length of time
cells spend in each stage.
Cell Count per Stage of Mitosis
Have students compare their sketches and data tables with other pairs. Discuss their data table
results as a class and find the class averages for the number of cells counted in each stage.
Ask the following question:
 In which stage do cells spend the most time? Interphase
Guided Inquiry
After students have observed the stages of mitosis in the onion root tip cells, have them
investigate the relative length of time that cells spend in each stage on their own. Students can
develop their own plans for collecting data based on their knowledge of the procedure and
materials used. Ask the students some guiding questions to help them focus their inquiry:
 How can you calculate the relative length of time cells spend in each stage?
 How will you identify cells in interphase?
For example, students may choose a field of view to observe and count the number of cells in
each stage within this view. Students may record their data in a table similar to the one below.
Students could also choose to observe several fields and compute the average cell count for
each stage.
Sample Data Table
Cell Count per Stage of Mitosis
Analysis and Conclusions:
Have students draw conclusions from their data about which stage is the longest and display
their data in an appropriate graph, such as a pie chart. Then have pairs discuss their procedure
and conclusions with other pairs. Were their findings and conclusions the same? What might
account for differences in the findings? Encourage students to constructively evaluate and
critique each other’s procedures.
1. In which phase were the greatest number of cells in? In which phase were the smallest
number of cells in? Use data to support your answer. Answers will vary according to student
data. Interphase is the longest phase of the cell cycle. Metaphase is the longest phase of
mitosis. Anaphase is the shortest phase.
2. What criteria did you use to identify the stages of mitosis? Sample answer: We used the
shape and position of the chromosomes to identify the stages of mitosis.
3. Assume the cell cycles of neighboring cells are not dependent on each other. How could you
estimate how much time cells spend in each phase of mitosis with only a single view of cells at
one point in time? Sample answer: In a large group of cells, the number of cells in each phase
represents the portion of time any random cell spends in each phase. Thus if more cells were in
a specific phase at any point in time, then that phase must last longer than other phases.
4. How do your observations in this investigation support the cell theory? Sample answer: We
observed cells that were undergoing cell division to create daughter cells. This observation
demonstrates that cells arise from pre-existing cells.
Further Questions
5. Why was an onion root tip used to observe mitosis, rather than a different part of the onion?
Since the onion roots are growing the cells in the tip are dividing quickly. This means there are
many opportunities to view mitosis in this tissue.
6. Based on your data from the spreadsheet, in which stage do you think cells spend the
greatest percentage of time?
Because more were in interphase than any other stage it seems likely that cells spend
the greatest percentage of their time in interphase.






Inquiry and Nature of Science Skills in this Lab:
Design Investigations
o Design and conduct investigations using:
 Sample (if needed) - a portion of the affected elements in an investigation
used to extrapolate what would have happened to a larger set of
elements
o Practice lab safety by:
 Following lab safety procedures
 Recognizing safety equipment and materials and knowing their proper
use
Gather Data
o Choose appropriate tools to conduct an investigation:
 Microscope
 Slides and cover slips
o Use senses to observe:
 Seeing (color, shape, size, texture, motion)
o Use the appropriate format to record data:
 Graph
 Chart
 Sketch
Interpret Data
o Sort and classify using scientific reasoning by:
 Sorting objects, substances and organisms by characteristic
o Identify and interpret patterns using:
 Trends in data
 Tables and graphs
 Analysis of data collected during an investigation
Evaluate Evidence
o Draw and support a conclusion by:
 Reporting trends and patterns in the data
Communication in Science
o Report results using:
 Peer presentation
 Table/graph showing data
Analyze Scientific Results
o Participate in critiquing/peer review by:
 Evaluating an investigative design
 Evaluating data for accuracy
 Evaluating a conclusion



Patterns and Systems
o Patterns and Change:
 Many patterns in nature occur in cycles.
 Cycles may be short, such as the second hand of a clock, or long such as
the cycle of a year.
Scientific Investigation
 Scientific Investigation:
 When a scientific investigation is repeated, a similar result is expected
o Scientific Data and Outcomes:
 Results of similar scientific investigations may turn out differently because
of inconsistencies in methods, materials, and observations.
Scientific Endeavor
o Characteristics of Science:
 Scientific claims can be substantiated using data and observation.