Name _________________________________ Period _____ Date _________________
Mitosis Lab
Objectives
 To recognize the stages of mitosis in plant cells.
 To use a microscope to observe cells
 To make accurate diagrams of microscopic observations
 To make comparisons between cells at different stages of division.
Background
Cells are limited in size due to their ability to exchange nutrients and wastes with the
environment. In order for multicellular organisms to grow, once a cell reaches a certain size
the cell must divide. The process of cell division involves the replication of the nucleus
(mitosis) and the division of the cytoplasm (cytokinesis). Mitosis in the higher plant cells
takes place in regions called meristems (regions of the plant that are actively growing) that
are found in the tips of roots and stems. In animals mitosis can take part all over the
organism, where ever new cells are required. However, some tissues undergo division
more than others e.g. skin tissue; while cells in other tissues rarely divide once they have
reached maturity e.g. brain and heart tissue.
Hypothesis – 5 pt. make a hypothesis regarding which stage will take the longest time
Materials – Microscope, onion root tip slides, pencil, calculator
Procedure
Examine the prepared slides available. Locate the meristematic region (actively growing) of
the onions (near the tips) with the 10X objective. Then put the 40X in place and fine focus
to study individual cells. Identify cells that clearly represent the different phases of division.
Sketch accurate, labeled diagrams of the cells in the boxes provided. Each cell should fill
the entire box, be in as much detail as possible, and be labeled with as many structures as
you can identify. Cell membrane, cell wall, nucleus, nuclear membrane, nucleolus,
chromosomes, centromere, spindle fibers. You can do observations any order
1. Interphase.
The nucleus may have one or more dark stained
nucleoli and is filled with a network of threads, the
chromatin. During the S Phase of interphase
DNA replication occurs.
2. Prophase
The first sign of division occurs in
prophase. Here the replicated
chromosomes joined by a centromere
begin to coil and thicken. In late prophase
the nuclear membrane and nucleoli
disappears.
4. Anaphase
At the beginning of anaphase, the
chromosomes are separated and moved ,
by the spindle fibers to the poles of the
cell.
3. Metaphase
The spindle apparatus appears in the
cytoplasm. At metaphase, the
chromosomes have moved to the center
of the cell, moved by the spindle fibers.
the centromeres are attached to the
spindle fibers
5. Telophase
During telophase the nuclear membrane
reforms the spindle fibers disappear.
Cytokinesis occurs dividing the cell in two
daughter cells.
Questions. Answer here 5 pts each
1. Explain why we studied the tip of the onion root for observing mitosis.
2. Explain how the process of mitosis helps an organism to grow in size.
3. Why do organisms not increase in size simply by growing bigger and bigger cells?
Analysis –
A student is interested in the percentage of time a cell spends in each stage of the cell
cycle. So the student carefully counts the number of cells at each stage of the cell cycle,
and their data are listed below. Your job is to calculate the percentage of cells at each stage
of the cell cycle and mitosis.
We will use the sample onion slide below on next page
a) Identify stage of cells Use the microscope slide of the onion on next page and
determine which stage each of the cells marked with an X is in.
Write stage next to the x.
b) Average Total time for onion root tip cells to go through ALL stages is:
24 hours, or 1440 minutes. This is placed in table already for you
c) Count and record the number of cells marked with an 'X' that are in each phase in
the slide above (In a lab, you would count at least 200 cells by moving your slide so
that you view several fields.) Record your observations in table below.
d) Determine the total number of cells counted. Enter this number at the bottom of
table in box
e) Determine the percent of cells that are in each phase. Divide number of cells in
each stage by total cells counted. Leave as decimal. Round to nearest 100’s place.
Ex. 22% write as .22
f) Calculate the time (in minutes) for each phase Multiply the percent of cells in
each phase by the number of minutes for the whole cycle. Ex. .22 X 1440 = 317
mins. Record in table
Data table 15 pts
Stage
Interphase
Prophase
Metaphase
Anaphase
Telophase
TOTAL
# of cells
Percent of cells
#cells in stage / total cells
Time in each stage (min)
% cells X total time
1.00 (=100%)
Total = 1440 min
What stage is the onion root tip cell in most of the time? The least amount of time? List
here and then put the answer in your conclusion and relate to your hypothesis.
Conclusion – 12 pt rubric. On separate lined paper, write a one page conclusion
summarizing the mitosis lab. Typing is optional but it must be neat and legible! This
conclusion should be at least 3 paragraphs, one for each part. Attach to report.
a) Introduction – Include appropriate background information about how cells grow,
mitosis, and your hypothesis.
b) Body – Describe procedures of how you observed the cells in mitosis and what you
were able to observe in each stage. Describe the time analysis you did below and
how you calculated the time each cell spends in each stage
c) Conclusion – What were the results of your time analysis? Did they agree with your
hypothesis? Sum up your findings about mitosis
ONLINE MAKE UP
http://www.instruction.greenriver.edu
 Faculty Web pages
 Ken Marr
 Biology 211
 Lab activities/handouts (upper Left)
 Lab 8 Photomicrographs of mitosis in onion root tip