Cell Division and Mitosis

Nicholas DiGiovanni Naperville Central High School
440 W Aurora
Naperville IL 60540


1. For grades 9-12 (may be modified for younger).
2. Students will make a slide of onion root tips and observe different phases of
3. Students will be able to state why cells divide.
4. Students will draw the different stages of mitosis and try to arrange them in
order of division.
5. Students will demonstrate each phase of mitosis and the main characteristics
of each.


1. Prepared onion root tip mitosis slides.
2. In place of these and to promote interest, students may set up their own
slides. Materials needed per slide are: fresh grown onion root tip, 5-10ml
distilled water, 5ml 6M HCl, 1 ml Feulgen reagent in a vial, 5 ml 45% acetic
acid, dropper pipette per solution, beaker, slide, coverslip, and a pencil with
eraser or small cork to squash the slide. Materials needed per class are: 5-10
ml Carnoy's solution (1 glacial acetic acid : 3 absolute alcohol) in vial, 2-3
cups and onions, and toothpicks.
3. A microscope per student or pair.
4. Two different colored pipe cleaners cut at varied lengths to represent
chromosomes for assessment (4 chromosomes per cell). I use 2 long and 2 short
blue pipe cleaners and 2 long and 2 short red pipe cleaners connected with beads
which represent the centromeres. This model would use the long pipe cleaners
as a homologous pair of chromosomes and the short as another pair. Two pipe
cleaners of each size and color are used to model replication. Each chromosome
is composed of two chromatids.


This lesson would be used after cells have been observed with microscopes in the
lab. After a review of cell parts, the teacher would exhibit the onion (or
prepared slides) and explain that root tips have been cut for the students to
observe. Explain that the stain to be used in this preparation is different
because something will be noticeable that could not be seen in past labs
(chromosomes). Try to have the students guess this by questioning them about
the cells they are observing - i.e. dividing cells - and how these are different
than previous cells observed. Nuclei were observed before but not the

LAB Students are more eager to learn how to set up their own slides and observe them than to use a prepared slide with which they may be unfamiliar. Steps 1-8 explain slide preparation. Go to #9 if prepared slides are being used. 1. Advance preparation: a. Take an ordinary yellow onion. Cut off any old root growth. Place the onion in a cup of water so that only the root portion is under water. To do this, push toothpicks into the side of the onion which extend outward and hold it on the rim of the cup. New roots should grow within two days. b. Cut off .5-1 cm of growth at the root tip - enough for all the students. c. Transfer immediately to Carnoy's solution. After 24 hours, roots should be stored in 70% ethanol in a refrigerator. This stops cell division. (Steps 2-9 to be completed by students) 2. Obtain a root tip. 3. After obtaining the root tip, pour off the fixative and replace it with 2-5 ml distilled water. Solutions may be poured into a beaker or down the drain. 4. After 1 minute remove the water with a pipette and add 2-5 ml 6M HCl. 5. After 3 minutes carefully remove the acid and wash tissue off with distilled water. Agitate the vial for 1-2 minutes. Discard the water. 6. Use forceps to transfer the tissue to a vial containing 1-2 ml Feulgen reagent. The reagent may be added to this vial if desired. (CAUTION: this dye will stain hands and clothes permanently.) After 20 minutes use forceps to transfer the tissue to a vial containing 5 ml 45% acetic acid. 7. Place 1-2 drops of acetic acid onto a microscope slide and transfer the tissue to the drop. Using dissecting pins and razor blades tease and macerate the tissue into tiny pieces. 8. Place a coverslip over the macerated tissue trying not to get air bubbles under the coverslip. Press down firmly onto the coverslip with a small cork or pencil eraser to spread the cells in a very thin layer. Push down in a perpendicular direction and the coverslip should not break. 9. Once the slide has been prepared or obtained from the teacher, observe it and draw all the different views of cells present under high power. Be careful to observe the nucleus and chromosomes since this is what was not observed previously. Discussion 1. During the 20 minute stain time (Step 6) it is important to have the students discuss what the cells are doing. Since these cells are in the root tip, they are rapidly dividing. During normal cell activity the chromosomes are unwound and too thin to be seen. During cell division, chromosomes thicken, take up stain and can be easily observed. The students should also try to come up with reasons why cells divide (possible answers: to grow, to repair or replace damaged cells, to reproduce, or to differentiate in the cell cycle of multicellular organisms). Although it is better to have the students elicit these, it may be necessary to give them some of the reasons since this is an introduction. Also at this time explain what is happening in interphase. Cells need to replicate the chromosomes before dividing to ensure that the newly formed cells contain the same genetic material (chromosomes). 2. What the students are observing is an ordered process by which the cells divide the chromosomes so that one copy of each goes to each new cell. Once they have drawn all the different views of cells they have observed, they should share them with their lab groups, the teacher and perhaps the class. Hopefully all the stages of mitosis have been observed and drawn. These can be put on the board or overhead so that the entire class can see all the phases/views and copy them onto their papers. It is not necessary to name the observed cells with a phase of mitosis, but it may be easier so that students can more easily differentiate them and relate them to a new vocabulary term. Once all the students have drawings of all the phases of mitosis, ask them to arrange the pictures in a way which would show a logical sequence of cell division. 3. Have one member from each group explain what order they put the drawings and why they did it that way. After all students have explained their process, students may wish to choose the model that they think is best. Students should now look into their textbooks to find out what is happening in each phase and how the text organizes the phases of mitosis. Assessment:

1. Students are to make a model of a cell which is in the process of mitosis and
cell division. They should draw on their paper the border of a cell which is
dividing. These need to be big enough so that the pipe cleaners can be put
inside. There needs to be a cell border for interphase, prophase (perhaps one
for early and late prophase), metaphase, a partially dividing cell for anaphase,
a nearly totally divided cell for telophase, and two new cells for the daughter

2. Students will take the pipe cleaners and place them in the "cells". They
should arrange four "chromosomes" properly in the various phases of mitosis.
The pipe cleaners may be taped or glued on the paper and a description written
which describes the events occurring within the cell. The pipe cleaners may be
manipulated and each phase described to the teacher. Students may work in
groups of four and only one student from each group would be tested to save time
evaluating the mitosis demonstration.

3. The teacher should determine the grading method, points or letter grade, but
a recommended method would be: 5 for all the phases demonstrated exemplary in
proper order with a detailed description of each. 4 for correct demonstration
of phases and clear description. 3 for a generally correct model but lacking
some clarity and detail. 2 for a partial demonstration, perhaps the phases are
out of order or improperly shown and the description is incoherent. 1 for an
incorrect demonstration of model and explanation.

Other notes:

1. For a multicultural emphasis on teaching, students can observe that different
organisms have cells which look very similar. Different races and nationalities
of people must have cells which are not distinguishable from each other.

2. It may not be necessary to use a visible pipe cleaner model to better
understand mitosis, but when teaching meiosis the model is very good to
demonstrate crossing over and variable gamete formation as well as differences
from mitosis.
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