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iCopyright © 2013 National Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us online at www.nms.org.

Middle Grades Science

MATERIALS AND RESOURCES

EACH GROUP TEACHER

paper towels

scissors

string

teacher-provided materials

bag, zipper-lock, quart

beads, pony

Skittles®, single size bag

MultiplicityModeling the Cell Cycle

ABOUT THIS LESSON

This three-part lesson will familiarize students with the events of the cell cycle. Part I asks students to think analogously about mitosis

and cytokinesis by having them divide a “toy” collection. Part II is a deliberate discussion about cell division during which students map out a “schedule of events” for cell division. Part III is teacher directed. Using paper manipulatives, teachers lead students through the stages of the cell cycle, beginning with late interphase and ending with cytokinesis.

OBJECTIVES

Students will:• Locate the correct structures of the cell

undergoing mitosis as the teacher describes the function

• Model the processes of mitosis and cytokinesis

LEVEL

Middle Grades: Life

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Middle Grades Science – Multiplicity

NEXT GENERATION SCIENCE STANDARDS

DEVELOPING ANDUSING MODELS

SYSTEMS ANDSYSTEM MODELS

LS1: STRUCTURESAND PROCESSES

CONNECTIONS TO AP*

2BIOLOGYBIOLOGYAPAP

*Advanced Placement® and AP® are registered trademarks of the College Entrance Examination Board. The College Board was not involved in the production of this product.

LESSON CONSUMABLES

Item 1 – Chromosome Manipulative (1/2)Item 2 – Chromosome Manipulative (2/2)

COMMON CORE STATE STANDARDS

(LITERACY) RST.6-8.1

Cite specific textual evidence to support analysis of science and technical text.

(LITERACY) RST.6-8.3

Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.

(LITERACY) WHST.6-8.1

Write arguments focused on discipline-specific content.

(LITERACY) WHST.6-8.2

Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.

ASSESSMENTS

The following assessments are embedded in this lesson:

• Assessment of prior knowledge of cell structure• Student-led modeling of cell cycle• Demonstration of random stages in the cell cycle

The following assessments are located on our website:• Lesson Assessment: Mitosis, Mardi Gras Style • Middle Grades Life: Heredity

ACKNOWLEDGEMENTS

Skittles® is a registered trademark of the Wm. Wrigley Jr. Company, a division of Mars, Inc.

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TEACHING SUGGESTIONS

This lesson is three-part activity that uses candies and paper chromosomes to help students learn the stages of the cell cycle. Part

I is a scenario in which students must figure out a way to divide their toy collection so that they may donate their duplicates to charity. Although quite simple, this part of the activity is meant to help students think analogously about the events that must occur during cell division.

In Part I, students will grasp that a system is required to divide the toys. Just as the daughter cells result from a series of regulated steps so, too, is the division of toys not random. It is important for you to ask questions that will lead students to understand that mitosis differs in the fact that a parent cell has the exact same number of chromosomes as the two daughter cells. This gives you an opportunity to emphasize that cell mitosis and the subsequent cytokinesis is not simply “dividing in half.”

This lesson uses candies and pony beads contained in a plastic sandwich bag to represent the “mess” that students must organize before separating out their “toys.” Other items can be used as long as there is a subset that can be separated from the larger “mess.” Colored paper clips can be separated from a larger collection of office supplies, for example. Also, be sure that whatever items represent the toys in this scenario are present in an even number to facilitate the equal distribution of toys and thus genetic material. A sample plastic bag might include four red, two green, four yellow, two orange, and two purple candies and any number of colored pony beads.

Part II is a deliberate discussion in which students map out a “schedule of events” of cell division. At this point, students do not need to know the exact terminology of chromatin, chromosome, and sister chromatid. You can name them if the students begin to describe these structures. However, they will need to be familiar with cytoplasm, cell membrane, and nuclear membrane. Encourage students to think about these structures and what—if any—changes must occur for the chromosomes to duplicate and the cell to divide. Suggested bell work would be to ask your students to label the parts of a cell which would also serve as a quick formative assessment.

Part III is teacher-directed. After identifying and describing the paper manipulatives, you will lead students through the stages of the cell cycle beginning with late interphase and ending with cytokinesis. Note that the homologous chromosomes have the same shape but may have different striping to represent different alleles. Be sure students have enough string to create a cell membrane, nuclear membrane, and eight spindle fibers (one for each of the chromosomes).

Go through the stages once without student input, allowing time for students to record their observations. During the second pass-through, encourage students to tell you how the manipulatives should appear. During the third pass-through, call out random stages of the cell cycle and ask your students to demonstrate these stages using their manipulatives.

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TEACHING SUGGESTIONS (CONTINUED)

THE CELL CYCLE

Individual cells within an organism go through various stages of growth and division. These stages are referred to as the cell cycle. The life cycle of a cell, or the cell cycle, can be separated into two main phases: interphase and cell division.

Interphase is the longest portion of the cell’s life cycle and is typically referred to as a “cell at rest.” The cell is not truly resting at this point, but rather it is not undergoing cellular division or mitosis. Cell division, the second phase of the cell cycle, takes place to create genetically identical daughter cells. In multicellular organisms, cells undergo cell division for the organisms to develop. Single-celled organisms that undergo mitotic cell division do so to reproduce.

Eukaryotic cell division consists of two stages: mitosis and cytokinesis. Mitosis is the duplication of the chromosomes and results in the formation of two nuclei. Cytokinesis is the distribution of the organelles and cytoplasm and results in the formation of two identical daughter cells. When cells are damaged or as cells die, new cells must be created to replace these cells. The mitosis phase consists of four stages.

INTERPHASE

The cell is between divisions during interphase, which consists of three phases: G1, S, and G2. During G1 the cell is typically “at rest” and undergoing protein synthesis. The uncoiled DNA is in the nucleus and called chromatin. During the S phase, DNA undergoes DNA replication. During the G2 phase, the cell continues to swell and some proteins continue to be formed while the centrioles complete duplication

inside the centrosome (“inter-” means between).

PROPHASE

The long, stringy, unwound chromatin fibers coil and condense into thick threads of visible genetic material called chromosomes. As the cell enters prophase, the chromosomes have already been replicated forming sister chromatids. The sister chromatids are connected to each other at the centromere. The spindle apparatus begins to form and the nuclear membrane breaks down while the nucleolus disappears (“pro-” means first or before).

METAPHASE

The centromeres of the sister chromatids line up along the center, or metaphase plate, of the cell bringing the genetic material to the center of the cell. Microtubules connect the centromere of each chromosome to the spindle apparatus via the centriole (“meta-” means middle).

ANAPHASE

The centromere of each chromosome divides, separating the sister chromatids from each other. The sister chromatids are separated because the spindle apparatus is becoming shorter, thereby pulling the chromatids to opposite sides of the cell. The chromatids of each pair will be moved by the spindle fibers toward opposite poles of the cell. The separated chromatids are called chromosomes. This separation allows one copy of each type of chromosome to be placed on opposite sides of the dividing cell (“ana-” means away).

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TEACHING SUGGESTIONS (CONTINUED)

TELOPHASE

The final stage of mitosis occurs as new nuclear membranes are formed around both groups of chromosomes. The result is two separate nuclei, each containing the same genetic information as the original cell’s nucleus. The chromosome will uncoil and loosen up to form chromatin threads. The spindle fibers break apart, and nucleoli are reformed. (“telo-” means end or far away).

CYTOKINESIS

The cell may now undergo the final stage of the cell cycle in which the cytoplasm divides. In animal cells, the onset of cytokinesis is marked by the presence of a cleavage furrow. The cell membrane is drawn inward until the cytoplasm is split into two separate parts forming two distinct cells. In plant cell, cells cytokinesis results from the formation of a cell plate between the two newly formed nuclei. As the cell wall grows, it separates the nuclei into two distinct cells (“cyto” means cell and “kinesis” means movement).

GLOSSARY

Centromere – The centralized region joining two sister chromatids.

Centrosome – The centrosome is also called the “microtubule organizing center.” The centrosomes in animal cells contain the centrioles. Centrosomes are found in plant cells but do not contain centrioles.

Chromatid – One half of a replicated chromosome.

Chromatin – The aggregate mass of dispersed genetic material formed of DNA and protein and observed between periods of cell division in eukaryotic cells.

Chromosome – Structure containing genetic information in the nucleus of all eukaryotic cells and visible during mitosis and meiosis. Chromosomes consist of DNA and protein.

Sister chromatids – Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis.

Spindle fiber – A grouping of microtubules that move chromosomes during cell division. This is also known as the spindle apparatus.

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Middle Grades Science – MultiplicityMiddle Grades Science – Multiplicity

DATA AND OBSERVATIONS

PART III: MODELING THE CELL CYCLE

Table 1. Important Structures of Cell Division

Structure Illustration Summary

Chromatin The uncoiled DNA is in the nucleus and is called chromatin.

Chromosome The long, stringy, unwound chromatin fibers coil and condense into thick threads of visible genetic material called chromosomes.

Sister chromatid Chromosomes have already been replicated, forming sister chromatids. The sister chromatids are connected to each other at the centromere.

Centromere The attachment point for spindle fibers to the chromosome.

Centriole Help create and organize the mitotic spindle fibers.

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DATA AND OBSERVATIONS (CONTINUED)

Table 2. Stages of Cell Division

Stage Illustration Summary

End of interphase

The cell is between divisions during interphase, which consists of three phases: G1, S, and G2. During G1, the cell is typically “at rest” and undergoing protein synthesis. The chromosomes are coiled together in the nucleus and are called chromatin.

Prophase The long, stringy, unwound chromatin fibers coil and condense into thick threads of visible genetic material called chromosomes.

Metaphase The centromeres of the sister chromatids line up along the center, or metaphase plate, of the cell, bringing the genetic material to the center of the cell.

Anaphase The centromere of each chromosome divides, separating the sister chromatids from each other. The chromatids of each pair will be moved by the spindle fibers toward opposite poles of the cell. The separated chromatids are called chromosomes.

Telophase The final stage of mitosis occurs as new nuclear membranes are formed around both groups of chromosomes. The result is two separate nuclei, each containing the same genetic information as the original cell’s nucleus.

Cytokinesis The final stage of the cell cycle in which the cytoplasm divides. In animal cells, the onset of cytokinesis is marked by the presence of a cleavage furrow. The cell membrane is drawn inward until the cytoplasm is split into two separate parts, forming two distinct cells.

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ANALYSIS

1. Go back and review your procedure for separating and donating your toys. Identify steps in your procedure that are similar to stages in the cell cycle.Answers will vary.

2. A complete set of chromosomes for an organism that reproduces sexually consists of genetic material from a father and mother. This number is described as 2n. Somatic cells in humans have 2n = 46 chromosomes. Assuming our model organism in Part III reproduces sexually, what is its value of 2n?2n = 4

3. How many chromosomes does the organism in Part III have during each of the modeled stages detailed in Table 3?

Table 3. Chromosome Numbers During the Cell Cycle

Stage Number of Chromosomes in the Cell

End of interphase 4

Prophase 4

Metaphase 4

Anaphase 8

Telophase 8

Cytokinesis 4

CONCLUSION QUESTIONS

1. Models and simulations are useful because they allow us to study phenomena that are otherwise too small or too complicated to observe. Few models can replicate the actual phenomenon perfectly, however. Identify and explain one limitation of Part I, the toy activity.Answers will vary. Cells undergoing mitosis begin and end with the same number of chromosomes.

2. The illustrations shown in Figure 1 are of onion (Allium cepa) root tip cells in various stages of the cell cycle. Look at the center cell of each illustration and determine if the cell is in interphase, prophase, metaphase, anaphase, or telophase. Record the stage on the line provided below the image.Stages from left to right:• Prophase• Anaphase• Interphase• Telophase• Metaphase

3. After examining a prepared slide of an onion root tip, a student observes that some stages of the cell cycle are more prevalent than others. The number of cells she counted in each stage is recorded in Table 4.Develop a pie graph representing the data from Table 4.See Figure A.

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CONCLUSION QUESTIONS (CONTINUED)

Figure A. Percentages of chromosome numbers during the cell cycle

4. The cell cycle for an onion root tip cell lasts 12 hours. Determine the amount of time in minutes that each stage lasts. Assume that the likelihood of observing a cell in a particular stage directly relates to the time the cell spends in that stage.a. Interphase – 562 minutesb. Prophase – 101 minutesc. Metaphase – 36 minutesd. Anaphase – 7 minutese. Telophase – 14 minutes

5. A cell in interphase in the leaf of a tomato plant has 12 chromosomes. A second cell in the plant is undergoing mitosis. Under the microscope, it appears as though the chromatids are being pulled to the poles of the cell. Identify the stage of mitosis that the cell is in and determine the

number of chromosomes in the cell during this stage.The stage of mitosis is anaphase. During anaphase, this cell would have 24 chromosomes.

6. Tissue samples have been collected from a patient with lung cancer. It was discovered that the cancerous cells are undergoing mitosis at a more rapid pace than normal lung cells. How would this be detrimental to the healthy lung cells?When the cell is “at rest” in interphase, one of its main functions is to synthesize proteins. When cells are undergoing mitosis at a faster rate, the amount of time that the cell undergoes such normal functions as protein synthesis decreases. This will impact the tissue, the organ, the system and, ultimately, the entire organism.

Interphase

Prophase

Metaphase

Anaphase

Telophase

1Copyright © 2013 National Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us online at www.nms.org.

Middle Grades Science – MultiplicityMiddle Grades Science

MATERIALS

paper towels

scissors

string

teacher-provided materials

MultiplicityModeling the Cell Cycle

They say that growing up is hard to do. Getting older means understanding more about how the world works, greater responsibility, and knowing how our actions affect the world around us. It never stops. And as if you needed

one more reminder of how your world is changing, your mom has asked you to get rid of all of your duplicate toys.

“You have too many action figures, too many building blocks, too many dolls,” she says. “How do you have so many toys that are identical? We—you—can donate some of them. Go through your room and divide them up. I’ll bring you two boxes. Figure out an orderly way. Put the ones you want to keep in one box and the remaining toys in the other.”

It won’t be as easy as just splitting your toy collection in half, but it won’t be too difficult either. Your collection is large but you have those duplicates, so it will not be that big of a deal to give some away. But you survey your room, and it’s a mess. You need a plan. What is it?

Growing is a characteristic of life, and organisms grow when their cells get bigger or when they make new cells. The process of creating new cells from existing cells is called cell division and its exactly what it sounds like: dividing a cell into two cells. Mitosis is when the two cells created are identical. Unlike the boxes of toys, the daughter cells must each contain the same number of chromosomes as the parent cell.

Eukaryotic cell division consists of two phases: the division of nuclear material and the division of everything else into two cells. The division of nuclear material is called mitosis, and the division of the cytoplasm and all the organelles is known as cytokinesis. The end result of cell division, also called the M phase, is the formation of two identical daughter cells.

What happens when a cell is not dividing? It is doing what it is supposed to be doing. A liver cell is filtering wastes from your blood. Lung cells are facilitating the exchange of oxygen and carbon dioxide. This part of a cell’s life is called interphase. Interphase and M phase together make up the complete cell cycle of growth and division.

What does “eukaryotic” mean?

One way to remember what “cytokinesis”

means is to dissect the word and determine the

meaning of its parts. What is the prefix in

cytokinesis? The root word? What do they

mean?



PURPOSE

In this activity, you will generate a procedure to reliably separate duplicated toys (candies) and compare this process to the phases of the cell cycle.

PROCEDURE

PART I: THINKING ANALOGOUSLY

1. Remove the “toys” from the bag and spread them out.2. Generate a method of separating the “toys” in an orderly fashion.3. Record your procedure on your student answer pages.

PART II: ANTICIPATING MITOSIS

Cell division begins with one cell and ends with two identical daughter cells. What events have to occur for the daughter cells to have the same number of chromosomes as the mother cell? Develop a “schedule of events” or procedure for cell division and record your steps.


Using paper chromosomes and string, your teacher will model the cell cycle. With your own set of chromosomes and string, you will follow along.

On your student answer pages, you will record:• An illustration and description of each of the important structures of cell

division (Table 1)• An illustration and summary of each of the stages of the cell cycle (Table 2)

Be aware that although we have identified and named the stages of the cell cycle, the events occur in one continuous process.

Think about the structure of the cell. Are there certain structures

that are in the way or must change for cell

division to occur?



DATA AND OBSERVATIONS

PART I: THINKING ANALOGOUSLY

Use this space to record your procedure for separating your “toys.”

PART II: ANTICIPATING MITOSIS

Use this space to record your anticipated schedule of events for mitosis.





Table 1. Important Structures of Cell Division

Structure Illustration Summary

Chromatin

Chromosome

Sister chromatid

Centromere

Centriole




Table 2. Stages of Cell Division

Stage Illustration Summary

End of interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis



ANALYSIS

1. Go back and review your procedure for separating and donating your toys. Identify steps in your procedure that are similar to stages in the cell cycle.

2. A complete set of chromosomes for an organism that reproduces sexually consists of genetic material from a father and mother. This number is described as 2n. Somatic cells in humans have 2n = 46 chromosomes. Assuming our model organism in Part III reproduces sexually, what is its value of 2n?

3. How many chromosomes does the organism in Part III have during each of the modeled stages detailed in Table 3?

Table 3. Chromosome Numbers During the Cell Cycle

Stage Number of Chromosomes in the Cell

End of interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis



CONCLUSION QUESTIONS

1. Models and simulations are useful because they allow us to study phenomena that are otherwise too small or too complicated to observe. Few models can replicate the actual phenomenon perfectly, however. Identify and explain one limitation of Part I, the toy activity.

2. The illustrations shown in Figure 1 are of onion (Allium cepa) root tip cells in various stages of the cell cycle.

Look at the center cell of each illustration and determine if the cell is in interphase, prophase, metaphase, anaphase, or telophase. Record the stage on the line provided below the image.

Figure 1. Onion root tip cells




3. After examining a prepared slide of an onion root tip, a student observes that some stages of the cell cycle are more prevalent than others. The number of cells she counted in each stage is recorded in Table 4.

Table 4. Number of Cells in Each Phase

Cell Phase Numbers of Cells Observed

Interphase 78

Prophase 14

Metaphase 5

Anaphase 1

Telophase 2

Develop a pie graph representing the data from Table 4.

A pie graph is very similar to the face of a

clock.




4. The cell cycle for an onion root tip cell lasts 12 hours. Determine the amount of time in minutes that each stage lasts. Assume that the likelihood of observing a cell in a particular stage directly relates to the time the cell spends in that stage.a. Interphase

b. Prophase

c. Metaphase

d. Anaphase

e. Telophase

5. A cell in interphase in the leaf of a tomato plant has 12 chromosomes. A second cell in the plant is undergoing mitosis. Under the microscope, it appears as though the chromatids are being pulled to the poles of the cell. Identify the stage of mitosis that the cell is in and determine the number of chromosomes in the cell during this stage.




6. Tissue samples have been collected from a patient with lung cancer. It was discovered that the cancerous cells are undergoing mitosis at a more rapid pace than normal lung cells. How would this be detrimental to the healthy lung cells?

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ITEM 1 – CHROMOSOME MANIPULATIVE (1/2)

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ITEM 2 – CHROMOSOME MANIPULATIVE (2/2)

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