6: Mitosis Lab (Using Pop Beads)

Last updated

Jun 28, 2025
Save as PDF
- 5: Osmosis Lab
- 7: Respiration and Fermentation

$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$

$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$

$\newcommand{\id}{\mathrm{id}}$ $\newcommand{\Span}{\mathrm{span}}$

( \newcommand{\kernel}{\mathrm{null}\,}\) $\newcommand{\range}{\mathrm{range}\,}$

$\newcommand{\RealPart}{\mathrm{Re}}$ $\newcommand{\ImaginaryPart}{\mathrm{Im}}$

$\newcommand{\Argument}{\mathrm{Arg}}$ $\newcommand{\norm}[1]{\| #1 \|}$

$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$

$\newcommand{\Span}{\mathrm{span}}$

$\newcommand{\id}{\mathrm{id}}$

$\newcommand{\Span}{\mathrm{span}}$

$\newcommand{\kernel}{\mathrm{null}\,}$

$\newcommand{\range}{\mathrm{range}\,}$

$\newcommand{\RealPart}{\mathrm{Re}}$

$\newcommand{\ImaginaryPart}{\mathrm{Im}}$

$\newcommand{\Argument}{\mathrm{Arg}}$

$\newcommand{\norm}[1]{\| #1 \|}$

$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$

$\newcommand{\Span}{\mathrm{span}}$ $\newcommand{\AA}{\unicode[.8,0]{x212B}}$

$\newcommand{\vectorA}[1]{\vec{#1}} % arrow$

$\newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow$

$\newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$

$\newcommand{\vectorC}[1]{\textbf{#1}}$

$\newcommand{\vectorD}[1]{\overrightarrow{#1}}$

$\newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}}$

$\newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}}$

$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$

$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$

$\newcommand{\avec}{\mathbf a}$

$\newcommand{\bvec}{\mathbf b}$

$\newcommand{\cvec}{\mathbf c}$

$\newcommand{\dvec}{\mathbf d}$

$\newcommand{\dtil}{\widetilde{\mathbf d}}$

$\newcommand{\evec}{\mathbf e}$

$\newcommand{\fvec}{\mathbf f}$

$\newcommand{\nvec}{\mathbf n}$

$\newcommand{\pvec}{\mathbf p}$

$\newcommand{\qvec}{\mathbf q}$

$\newcommand{\svec}{\mathbf s}$

$\newcommand{\tvec}{\mathbf t}$

$\newcommand{\uvec}{\mathbf u}$

$\newcommand{\vvec}{\mathbf v}$

$\newcommand{\wvec}{\mathbf w}$

$\newcommand{\xvec}{\mathbf x}$

$\newcommand{\yvec}{\mathbf y}$

$\newcommand{\zvec}{\mathbf z}$

$\newcommand{\rvec}{\mathbf r}$

$\newcommand{\mvec}{\mathbf m}$

$\newcommand{\zerovec}{\mathbf 0}$

$\newcommand{\onevec}{\mathbf 1}$

$\newcommand{\real}{\mathbb R}$

$\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}$

$\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}$

$\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}$

$\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}$

$\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$

$\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$

$\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$

$\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$

$\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}$

$\newcommand{\laspan}[1]{\text{Span}\{#1\}}$

$\newcommand{\bcal}{\cal B}$

$\newcommand{\ccal}{\cal C}$

$\newcommand{\scal}{\cal S}$

$\newcommand{\wcal}{\cal W}$

$\newcommand{\ecal}{\cal E}$

$\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}$

$\newcommand{\gray}[1]{\color{gray}{#1}}$

$\newcommand{\lgray}[1]{\color{lightgray}{#1}}$

$\newcommand{\rank}{\operatorname{rank}}$

$\newcommand{\row}{\text{Row}}$

$\newcommand{\col}{\text{Col}}$

$\renewcommand{\row}{\text{Row}}$

$\newcommand{\nul}{\text{Nul}}$

$\newcommand{\var}{\text{Var}}$

$\newcommand{\corr}{\text{corr}}$

$\newcommand{\len}[1]{\left|#1\right|}$

$\newcommand{\bbar}{\overline{\bvec}}$

$\newcommand{\bhat}{\widehat{\bvec}}$

$\newcommand{\bperp}{\bvec^\perp}$

$\newcommand{\xhat}{\widehat{\xvec}}$

$\newcommand{\vhat}{\widehat{\vvec}}$

$\newcommand{\uhat}{\widehat{\uvec}}$

$\newcommand{\what}{\widehat{\wvec}}$

$\newcommand{\Sighat}{\widehat{\Sigma}}$

$\newcommand{\lt}{<}$

$\newcommand{\gt}{>}$

$\newcommand{\amp}{&}$

$\definecolor{fillinmathshade}{gray}{0.9}$

Purpose

This lab demonstrates the essential process of mitosis, a critical mechanism for cell division and organismal growth. Students will build models to visualize chromosomal changes during mitosis and reinforce their understanding of cellular processes through observation and data analysis. This knowledge is foundational for understanding growth, repair, and reproduction in multicellular organisms, as well as for future applications in medical, biological, and genetic research fields.

Tasks

Model the phases of mitosis using pop beads.
Observe and document the phases of mitosis in plant and animal cells under a microscope.
Calculate the relative time spent in each phase of the cell cycle.
Criteria for Success:
Accurately model and label each mitotic phase.
Successfully identify and document phases of mitosis using prepared slides.
Submit a completed worksheet with accurate calculations and thoughtful answers to analysis questions.

Timeline:

Pre-lab preparation: 20 minutes
Exercise 1: 30 minutes
Exercise 2-3: 45 minutes
Exercise 4: 20 minutes
Clean-up: 15 minutes

Introduction to Mitosis

In eukaryotic cells, the cell cycle is the period from the start of one cell division to the beginning of the next. The first stage of the cell cycle is called interphase. During interphase, the cell performs its regular functions and prepares for cell division. This is the phase where cells spend most of their time. In interphase, chromosomes are not visible because they are in a decondensed state, appearing as a tangled mass of thin DNA threads combined with proteins, known as chromatin. The nuclear membrane is present and visible, along with the nucleolus, a dense region inside the nucleus where ribosomes are assembled.

Interphase is made up of two gap phases, G1 and G2, during which the cell grows larger and produces new organelles, enzymes, and proteins needed for cell division. Between these gap phases is the S phase, where DNA replication occurs in preparation for cell division. At the start of the S phase, the chromosomes are single and unreplicated. By the end of the S phase, each chromosome has created an identical copy of itself, forming two sister chromatids. These sister chromatids are held tightly together at a region called the centromere and this is what forms the ‘X’ shape you may be familiar with when thinking about chromosomes. While the sister chromatids remain physically attached, they are considered one replicated chromosome. Later in the cell cycle, when the sister chromatids separate, they are recognized as individual chromosomes.

In animal cells, interphase is also when the centrosome, which is made up of two centrioles, is duplicated. During cell division, spindle fibers grow out from the centrosomes and extend outward, attaching

Figure $\PageIndex{2}$ : Chromosomes and sister chromatids

Interphase is followed by mitosis in somatic (body) cells or meiosis in reproductive cells. During these processes, replicated chromosomes and cytoplasm are divided through karyokinesis (nuclear division) and cytokinesis (cytoplasm division), respectively.

Chromosomes that are the same length, have the same centromere location, and carry the same genes in the same order are called homologous chromosomes. Human somatic cells contain pairs of homologous chromosomes, with one chromosome in each pair inherited from the mother and the other from the father. Cells with two copies of each chromosome are called diploid (2n, where n represents the number of unique chromosomes in a set). In contrast, human sex cells—eggs and sperm—contain only one copy of each chromosome and are called haploid (n). When a haploid sperm (n) and egg (n) combine during fertilization, they form a diploid zygote (2n).

MITOSIS

Mitosis is the process of nuclear division that produces two cells with the same number of chromosomes as the parent cell. Most human cells, such as skin, muscle, and bone, divide through mitosis. This process is essential for the normal growth and development of a multicellular eukaryotic organism from a fertilized egg (zygote) and for the growth, repair, and replacement of cells and tissues. At the end of mitosis, two daughter cells are formed, each identical to the original parent cell. In unicellular eukaryotes, mitosis also serves as a form of asexual reproduction.

Mitosis is a complex, carefully controlled process that occurs in four distinct phases: prophase, metaphase, anaphase, and telophase. Telophase is immediately followed by cytokinesis.

Prophase: The cell prepares for division as its chromatin coils and condenses into visible chromosomes. By late prophase, each chromosome consists of two sister chromatids joined at a centromere. Spindle fibers begin to form from the centrosomes, which start moving to opposite poles of the cell. During this stage, the nucleoli and nuclear membrane break down. (Figure 3)

Figure $\PageIndex{3}$ : Cell in prophase

Metaphase: During this phase, spindle fibers, known as kinetochore microtubules, attach to a specialized protein structure on each sister chromatid called the kinetochore. These fibers manipulate the chromosomes, aligning them along an imaginary plane in the center of the cell called the metaphase plate. This "plate" is not a physical structure but simply represents the position of the replicated chromosomes before they are separated.

Meanwhile, other spindle fibers called polar microtubules, which do not attach to the chromosomes, extend from the two centrosomes and overlap near the metaphase plate, helping to stabilize the spindle apparatus.

Figure $\PageIndex{4}$ : Spindle fibers attaching to kinetochores in metaphase

Anaphase: The centromeres split with the help of separase enzymes, separating the sister chromatids. This occurs simultaneously for all chromosomes. The kinetochore spindle fibers shorten, pulling each chromatid toward the centrosome at the pole from which the fiber originated. This ensures that exactly half of the chromosomal material is evenly distributed to each side of the cell. In late anaphase, the non-kinetochore spindle fibers elongate, stretching the cell and preparing it for division.

Telophase: The non-kinetochore microtubules continue to elongate, stretching the cell further in preparation for cytokinesis (the division of the cytoplasm). The chromosomes arrive at their respective poles, and the kinetochores disappear. Two new nuclear membranes begin to form around the chromosomes in each half of the cell. Nucleoli reappear, and the chromosomes start to decondense back into their thread-like chromatin form. At the end of this stage, mitosis is complete.

Cytokinesis (splitting of the cytoplasm):
In animal cells and other eukaryotic cells without a cell wall, cytokinesis occurs through a "belt" of protein fibers near the cell's equator. These fibers slide past each other, tightening and forming a cleavage furrow around the cell. As the furrow deepens, it eventually pinches the cell into two separate cells.

In plant cells, the rigid cell wall prevents this type of constriction. Instead, vesicles from the Golgi apparatus deliver membrane proteins to the cell's interior at right angles to the spindle. These vesicles fuse to form a growing structure called the cell plate. The cell plate expands outward until it reaches and fuses with the plasma membrane, dividing the cell into two distinct daughter cells.

The Phases of Mitosis

Exercise 1: Modeling the Phases of Mitosis with Pop Beads

Models are an excellent way to represent natural structures and processes that are too small, too large, or too complex to observe directly. In this activity, you’ll use pop beads to build chromosomes and manipulate them to simulate cell division (mitosis and meiosis). This hands-on approach will help you better understand chromosomes and the cellular structures involved in cell division.

Your model cell will represent a diploid (2n) cell with four chromosomes, organized into two homologous pairs. To distinguish the homologous pairs, one pair will be longer than the other. Each homologous pair consists of one red chromosome (representing maternal DNA contributed by the egg) and one yellow chromosome (representing paternal DNA contributed by the sperm). This means that for each homologous pair, one chromosome will be red, and the other will be yellow.

During the G1, S, and G2 phases, the strands of pop beads represent chromatin, which is the uncondensed form of DNA. As the cell progresses through mitosis, the pop beads will represent chromosomes in their condensed state.

This diploid cell, with its two homologous pairs of chromosomes, will be modeled as it moves through the following stages of mitosis:

Interphase (G1): Uncondensed DNA before DNA synthesis
Interphase (G2): Uncondensed DNA after DNA synthesis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

By following these steps, you’ll gain a clearer understanding of the process of mitosis and how chromosomes behave during cell division.

Safety Guidelines for Mitosis Lab

● Handle pop beads and magnetic centromeres carefully to avoid injury or material damage.

● Keep liquids away from the microscope and electronic equipment.

● Follow proper microscope handling protocols to avoid damage.

● Dispose of waste materials (e.g., paper towels) in designated bins.

Group Size and Roles

Recommended Group Size: 3-4 students

Suggested Roles:

Recorder: Documents observations, completes the worksheet, and ensures group alignment.
Builder: Constructs chromosome models and ensures they align with instructions.
Microscope Handler: Operates the microscope and focuses on identifying mitotic phases (can be combined with Builder).
Data Analyst: Counts cells in different phases, perform calculations, and assists in graphing.

Materials:

Chalk (can be used directly on lab bench to draw cellular structures and then washed off)
Chromosome modeling kits
- Commercially available pop bead kits (e.g Carolina Biological Supply Company, Item #171100)
40 pop beads of one color (red)
40 pop beads of another color (yellow)
8 magnetic centromeres
Centromeres from kit
- OR 4 laminated pictures of centrosomes (each consisting of a pair of centrioles)
Paper towels / Kimwipes

Let me provide a detailed but organized version that maintains all the important information:

Exercise 1: Modeling Cell Division

Initial Chromosome Construction:

Build 2 pairs of homologous chromosomes (2n = 4)
First Homologous Pair (Long):
- One chromosome: 12 red beads
- Matching chromosome: 12 yellow beads
- Place magnetic centromeres at identical positions on both
Second Homologous Pair (Short):
- One chromosome: 6 red beads
- Matching chromosome: 6 yellow beads
- Place magnetic centromeres at identical positions on both

Interphase Modeling:

G1 Phase:

Using chalk, create a detailed cell drawing:
- Draw cell membrane
- Draw nucleus
- Draw nucleolus
Place one laminated centrosome in the cytoplasm
Position all 4 assembled chromosomes within the nucleus (representing chromatin mass)

Insert a Photo or drawing of G1 Here:

S Phase (DNA Replication):

For each of the 4 single chromosomes:
- Construct an identical second strand
- Connect the original and copy using magnetic centromeres
- These connected pairs are sister chromatids
Important: Consider the paired magnets as a single centromere unit, as in living cells the centromere remains unified until anaphase

Insert a Photo or drawing of S Here

G2 Phase:

Keep all 4 replicated chromosomes within the nucleus
Add a second laminated centrosome to the cytoplasm
Begin migrating both centrosomes toward opposite cell poles

Insert a Photo or drawing of G2 Here:

Mitosis Modeling

Prophase:

Maintain chromosome positions
Begin nuclear membrane breakdown simulation:
- Use paper towel/Kimwipe to partially erase nuclear membrane
- Completely erase the nucleolus
Continue centrosome migration to opposite sides
Draw spindle fibers extending from centrosomes toward chromosomes

Insert a Photo or drawing of Prophase Here:

Prometaphase:

Ensure centrosomes are positioned at exact opposite poles
Complete nuclear membrane breakdown
Draw two distinct types of spindle fibers:
- Kinetochore microtubules: Attach to chromosome centromeres
- Nonkinetochore microtubules: Radiate outward without kinetochore attachment

Insert a Photo or drawing of Prometaphase Here:

Metaphase:

Position chromosomes precisely:
- Align centromeres on an imaginary plane between centrosomes
- Place all chromosomes at the cell's equator
Maintain sister chromatid attachment at centromeres

Insert a Photo or drawing of Metaphase Here:

Anaphase:

Chromatid separation:
- Separate magnetic centromeres
- Move chromatids toward opposite poles
- Keep attachment to drawn kinetochore microtubules
Spindle fiber changes:
- Progressively erase and shorten kinetochore microtubules
- Extend non-kinetochore microtubules, creating middle overlap
Note: Each separated sister chromatid is now classified as an individual chromosome
Continue until chromosomes reach cell poles

Insert a Photo or drawing of Anaphase Here:

Telophase:

Chromosome arrangement:
- Gather chromosomes at each pole
- Complete spindle fiber erasure
Nuclear reconstruction:
- Draw new nuclear envelopes around chromosome clusters
- Add nucleoli-
Note: Chromosomes would normally begin to decondense into chromatin (though this cannot be modeled)

Insert a Photo or drawing of Telophase Here:

Cytokinesis:

For Animal/Fungal/Slime Mold Cells:

Maintain chromosome positions at poles
Create cleavage furrow:
- Draw membrane indentations inward toward cytoplasm
- Place indentations on non-centrosome sides
- Note: Actin and myosin proteins drive this process

For Plant Cells:

Show vesicle movement to cell center (equatorial plane)
Illustrate vesicle fusion forming cell plate
Indicate cell wall material release at plate
Show final division into separate cells

How do the daughter cells you formed compare to the original parent cell? _________________________________________________________________

Observe the phases of Mitosis in Plant Cells

Exercise 2: Observing the Phases of Mitosis in the Onion Root Tip

Materials:

Prepared slide of the onion root tip
Compound light microscope

Procedure:

Examine a slide of a longitudinal section of an onion root tip. Adjust the slide to view the region just above the root cap, where there are likely to be dividing cells.
Focus on the dividing cells using the 4x scanning objective lens, then switch to the 10x objective and then the 40x objective.
Survey the slide to find a cell in each phase of mitosis.
Draw or insert a picture of a cell for each phase in the boxes provided.

Interphase

DNA is uncondensed and in the form of chromatin. Individual chromosomes are not visible. The nuclear membrane is intact. The nucleolus is visible.

Prophase

Chromatin begins to condense into distinguishable chromosomes. These “puffy” structures are seen throughout the nucleus. Nucleoli begin to disappear. In late prophase (often called prometaphase) the nuclear membrane is no longer visible.

Metaphase

The chromosomes line up in the middle of the cell. Spindle fibers attach to kinetochores at the centromere and extend to the poles of the cell.

Anaphase

Centromeres split, separating each former chromatid into two individual chromosomes. The chromosomes move toward opposite poles.

Telophase and Cytokinesis

Chromosomes reach the poles. The nuclear envelopes begin to reform. The formation of a cell plate forms between the two cells to carry out cytokinesis

Observe the phases of Mitosis in Animal Cells

Exercise 3: Observing the Phases of Mitosis in the Whitefish Blastula

Materials:

Prepared slide of whitefish blastula
Compound light microscope

Procedure:

The blastula is an early embryonic stage where many of the cells are dividing at any one time.

Focus on the dividing cells using the 4x scanning objective lens, then switch to the 10x objective and then the 40x objective. Be sure to adjust the light settings for best results.
Survey the slide to find a cell in each phase of mitosis.
Most slides have 3 embryos. If you can’t find all the stages on a single embryo, be sure to check the others on the slide or get a different slide.
Draw or insert a picture of a cell for each phase in the boxes provided.

Interphase

The DNA is uncondensed and in the form of chromatin. Individual chromosomes are not visible. The nuclear membrane is intact. The nucleolus is visible.

Prophase

Chromatin begins to condense and chromosomes are distinguishable. These “puffy” structures are seen throughout the nucleus. The nucleoli begin to disappear. In late prophase (often called prometaphase) the nuclear membrane is no longer visible.

Metaphase

The chromosomes line up in the middle of the cell. Spindle fibers attach to kinetochores at the centromere and extend to the poles of the cell.

Anaphase

Centromeres split, separating each former chromatid into two individual chromosomes. The chromosomes move toward opposite poles.

Telophase and Cytokinesis

Chromosomes reach the poles. The nuclear envelopes begin to reform. A cleavage furrow forms between the two cells to carry out cytokinesis.

Why would the method of cytokinesis in animal cells not work in plant cells? Explain.

How Long Does a Cell Spend in Each Phase of the Cell Cycle?

Exercise 4: Determining Time Spent in Different Phases of the Cell Cycle (Optional)

Materials Needed:

Prepared microscope slides of onion root tip cross-sections
Microscope
OPTIONAL: Color printouts of onion root tip slides
Counter/clicker (optional)
Data collection sheet
Calculator

Background: The duration of each phase can be calculated by assuming that the percentage of cells found in each phase is proportional to the time spent in that phase. For example, if 20% of dividing cells are in metaphase, then cells spend approximately 20% of their mitotic time in metaphase.

Procedure:

Cell Observation

Microscope Setup and Orientation
- Focus your microscope on the root tip section at 400x magnification
- OR Obtain a color-printed photo of the slide for ease of counting
Identify the meristematic region where most cell division occurs
Practice identifying cells in different mitotic phases using your textbook/guide

Data Collection

Create a systematic pattern for scanning your slide to avoid counting the same cells twice. If using a printout, consider marking cells without obscuring the nucleus.
Count and record at least 200 cells total, noting:
- Number of cells in interphase
- Number of cells in prophase
- Number of cells in metaphase
- Number of cells in anaphase
- Number of cells in telophase

Calculations a. Calculate the mitotic index:

Mitotic Index = (Number of cells in mitosis ÷ Total cells counted) × 100
- Calculate the percentage of time spent in each phase:
Phase percentage = (Number of cells in phase ÷ Total dividing cells) × 100

Data Analysis

Create a table with your data
Convert percentages to time by assuming the total mitotic phase is 2 hours

Data Collection Table
Phase	Percentage	Time (minutes)
Prophase
Metaphase
Anaphase
Telophase
Total	100%	120 min

Questions for Analysis:

Which phase of mitosis appears to be the longest? The shortest? Explain why this might be biologically significant.

Calculate the percentage of cells that were not undergoing mitosis. What does this tell you about cell cycle duration?

Compare your results with those of other lab groups. What might account for any differences?

Practical Challenge Questions

In the circle below, sketch a 2n=6 diploid cell in metaphase of mitosis. Be sure to label the centromere, centrioles, and spindle fibers.

Figure $\PageIndex{1}$ : Paste Caption Here

References

Belwood, Jacqueline; Rogers, Brandy; and Christian, Jason, Foundations of Biology Lab Manual (Georgia Highlands College). “Lab 10: Mitosis & Meiosis,” (2019). Biological Sciences Open Textbooks. 18. CC-BY https ://oer.galileo.usg.edu/biology-textbooks/18

Alignment to Program Competencies

Program Competencies	Learning outcome
Explain the stages of the cell cycle and their significance.	Demonstrate knowledge of biological processes
Explain the stages of the cell cycle and their significance.	Demonstrate knowledge of biological processes
Analyze experimental data to infer biological processes.	Apply observational and analytical skills to biological data.