Lab 8. Cellular Division

LAB 8: Cellular Division

Name: ___________________

PRE-LAB QUESTIONS

Read the Introduction portions of Parts A/B and Parts C/D in their entirety. Answer the questions based on your reading.

Microscope Slides/ Modeling Cellular Division

1.

Why do cells undergo mitosis?

2.

What phase of cellular division do you expect to see the majority of cells in? What is the major event that occurs at this stage?

3.

What are the three major stages of the cell cycle?

4.

During mitosis the cell begins to separate the replicated genetic material into the newly developing daughter cells. Mitosis is subdivided into four stages: prophase, metaphase, anaphase, and telophase. During which stage of mitosis do the following occur? a.

______________ Chromosomes line up at the equator/center of the cell b.

______________ Nuclear membrane disappears/ Chromosomes condense c.

______________ Microtubules pull at the centrioles separating sister chromatids d.

______________ Nuclear membrane reappears/ Chromosomes decondense

5.

Name one way that cellular division differs in plant cells versus animal cells?

6.

What is a meristem? What can be seen by observing the meristem of the onion root?

7.

Name three ways in which mitosis differs from meiosis?


MITOSIS

PART A – Observing Cell Division in Microscope Slide - Onion Root Tip/ Whitefish Blastula

PART B – Using Pop beads to simulate the phases of mitosis.

Introduction –

Cell division is the process by which cells increase in number by making copies of themselves. The purpose of cell division is to allow some cells to reproduce, replace dead or damaged cells, and help tissues and organs grow. The type of cell division that makes growth, repair, and replacement cells is called mitosis. Mitosis results in the formation of two daughter cells that are genetically identical to each other and the original parent cell. Mitosis occurs in somatic (body) cells, which are cells not involved in sexual reproduction.

Almost all cells undergo a process of growth and division called the cell cycle . Cell division actually only makes up a small percentage of the cell cycle, with the majority of a cells life spent in preparation for the big divide! The cell cycle consists of three major stages – interphase, mitosis (PMAT), and cytokinesis. During interphase, the cell grows, matures, and undergoes DNA replication. Mitosis is the process by which the replicated DNA is separated into two separate nuclei. Mitosis can further be divided into four stages: prophase, metaphase, anaphase, and telophase. Cytokinesis, the last stage of cell division, is the division of the cell cytoplasm into the two newly forming cells. The completion of the cell cycle results in the formation of two genetically identical daughter cells from the division of a parent cell. Cells go through the cell cycle at different rates and at different types. The cells of the epidermis (skin) and lining of the digestive system need to be replaced on a daily basis whereas cell division in the liver and heart muscle is more rare. Mitosis occurs in throughout the body at different time intervals depending on the type of cell. For example, your body makes about 200 billion new red blood cells every day.

Stage 1 - Interphase: Cells spend the majority of the life in interphase preparing for division. This phase is subdivided into G1, S, G2. The major event that occurs is that DNA replicates.

Stage 2 - Mitosis: [PMAT]



Prophase: DNA condenses into chromosomes and become visible. The nuclear membrane begins to dissolve or break down. Formation of microtubules occurs which will migrate toward the poles (ends) of the cell, where they are anchored or suspended by centrioles.



Metaphase: Chromosomes align at the middle (equator) of the cell using microtubules as a support system. The chromosomes align themselves between the two poles. The microtubules grow long enough to attach to the chromosomes at their centromeres.



Anaphase: The microtubules pull and separate the sister chromatids from each other, pulling them toward the two poles of the cell.



Telophase: The nuclear membranes reforms and chromosomes decondense (no longer visible).

Telophase is the opposite of prophase.

Stage 3 - Cytokinesis: Division of the cytoplasm to form two new identical daughter cells which will enter the G1 phase of interphase. Plant cells form a cell plate, whereas, animal cells form a cleavage furrow.


During this lab activity, you will be observing cellular division in both plant and animal cells. Plants have regions of cell division where growth occurs – normally at the tips of stems and roots. This region is known as a meristem, and because this is an area of pronounced growth, many cells in this region are undergoing mitosis. One such region is the root tip, whose growth enables the roots to elongate and penetrate through the soil. After new cells are produced, they will enlarge and mature into different type of cells within the plant. One feature of plant cell mitosis that differs from animal cell mitosis is the presence of a cell plate indicating the cells are about to divide which gives the plant cells a more box-like appearance. Most plant cells also lack centrioles. When animal cells are about to divide they begin to form a cleavage furrow, which is more circular in structure. One of the best places to observe mitosis in animal cells is by looking at cells during early embryonic development. These cells are actively dividing by mitosis and will later differentiate to form various functions within an organism; some may even from tissues and complex organs.

Diagram of Mitosis:


Name: ______________________

PART A: Observing Cell Division in Microscope Slide - Onion Root Tip/ Whitefish Blastula

Overview Students will examine various slides illustrating the process of cellular division. They will identify and compare the various stages.

Materials for lab group of 2 students :

Access to Microscope

Microscope slides (Onion Root Tip, Whitefish blastula)

Part A1: Onion Root Tip – Plant Cell Mitosis

1.

Obtain a slide of an onion root tip. Place slide on the microscope and view under low power and then on medium power.

2.

Draw the slide as it appears under medium power. You do not have to draw every single cell, but try to draw at least 4 or 5 - illustrating at least 2 different phases of cellular division. Try to label one or two phases of cell division.

Magnification: _____X

Part A2: Whitefish Blastula – Animal Cell Mitosis

1.

Obtain a slide of whitefish blastula. Place slide on the microscope and view under low power and then on medium power.

2.


Magnification: _____X a.

Which phase of cellular division were the majority of the cells in? ________________________ b.

Name one way that plant cell mitosis differs from animal cell mitosis?


PART B: Using Pop beads to simulate the phases of mitosis.

Overview Students will simulate the phases of mitosis using pop beads.

Materials for lab group of 4 students:

40 Red pop beads /40 Yellow pop beads

2 Red centromeres /2 Yellow centromeres

4 Plastic tubular centrioles

Procedure –

1.

Construct your parent cell. Construct two strands of seven red pop beads and attach each strand to a red centromere. Repeat with two strands of seven yellow pop beads and a yellow centromere. There will represent a homologous pair of chromosomes. Your beads should look similar to the illustrations below.

RED YELLOW

a.

How many chromosomes does your parent cell have? _____ b.

How many daughter cells are created as a result of a cell undergoing mitosis? ______ c.

How many chromosomes do you expect to find in each of the daughter cells that are formed at the conclusion of mitosis? _____

2.

INTERPHASE: This stage is the longest stage of the cell cycle and prepares the cell for division. Though the distinct chromosomes are not visible, the genetic material is undergoing an important process – DNA replication.

You can illustrate the chromosome duplication that occurs during interphase by constructing two chromosomes identical to the ones you made previously. Each half of the duplicated chromosome is called a chromatid. Join both red chromatids at the centromere to form a pair of sister chromatids. Repeat for the yellow chromosome. Place a pair of plastic centrioles, at ninety degree angles, just outside of your nuclear membrane. The centrioles also replicate during interphase so place each pair next to them in the cell.

LAB 8: Cellular Division a.

Diagram Interphase as you have just simulated the process. The diagram of your chromosomes should look similar to the one illustrated underneath the beginning of this procedure. Be sure to include the centrioles in your diagram. b.

What is the major event that occurs during interphase? _____________________

3.

PROPHASE: This is the first stage of mitosis and results in the disappearance of the nuclear membrane, separation of centrioles to opposite poles and formation of spindle fibers. Illustrate prophase by moving your two pair of centrioles to opposite poles (sides) of the cell (your lab desk) a.

Diagram Prophase as you have just simulated it above. Be sure to include the centrioles in your diagram.

4.

METAPHASE: Chromosomes line up in the center of the cell or at the middle of the metaphase plate. The centromeres of each sister chromatid are attached, by spindle fibers, to the centrioles at the opposite poles of the cell. Illustrate metaphase of mitosis by centering your chromosomes along an imaginary metaphase plate

(center) with the centrioles still at opposite poles of the cell. Think M etaphase = M iddle! a.

Diagram Metaphase as you have just simulated it above. Be sure to include the centrioles in your diagram.


5.

ANAPHASE: Anaphase is characterized by the separation of the sister chromatids and their movement of the individual chromatids to the opposite poles of the cell. Think A naphase – Pulled A way. Simulate

Anaphase by separating and moving the centromeres of each chromosome toward opposite poles of the cell.

Notice how the arms of each chromosome trail the centromeres to the poles. a.

Diagram Anaphase as you have just simulated it above. Be sure to include the centrioles in your diagram.

6.

TELOPHASE: This phase is characterized by the reappearance of the nuclear membrane and disappearance of the spindle fibers (apparatus). The chromosomes begin to uncoil and are no longer clearly visible.

7.

CYTOKINESIS: Separates the cytoplasm into two discrete daughter cells.

Illustrate the final stages of cellular division by moving one strand and one yellow strand to the centrioles it was heading toward during anaphase. Imagine a cleavage furrow developing between each nuclei and separating the cell into two daughter cells. Note how each of your daughter cells now contains one red and one yellow chromosome, as well as one pair of centrioles, exactly like the cell with which you began with

(parent cell)!

a.

Diagram Telophase/ Cytokinesis as you have just simulated it above. Be sure to include the centrioles in your diagram. b.

A friend tells you that “prophase and telophase are opposite phases”. Are they correct? Explain your answer. c.

Did you illustrate the process of mitosis occurring in a plant or animal cell during this activity? How do you know? d.

How many cells are formed at the completion of mitosis? Are these cells identical or genetically different from the initial parent cell?


MEIOSIS

PART C – Observing Cell Division in Microscope Slide – Lily Sporangia

PART D – Using Pop beads to simulate the phases of Meiosis

Introduction -

Meiosis is another type of cellular division. It resembles mitosis in many ways however; the result of meiotic division is very different from that of mitotic division. Meiotic division results in the formation of gametes (egg and sperm), which contain half of the parental DNA. Each species has a characteristic number of chromosomes per somatic cell. The chromosomes exist as homologous pairs, each carrying the same genes. Humans have 46 chromosomes and therefore, 23 homologous pairs. The full complement of 46 chromosomes is referred to as the diploid number (because each chromosome is represented twice). Each gamete (egg or sperm) contains only one representative of each homologous pair (or half the diploid number). This is referred to as the haploid number .

Haploid (n) Egg + Haploid (n) Sperm = Diploid (2n) Zygote

The mechanism responsible for the creation of haploid gametes is meiosis. Meiosis consists of two divisions.

Meiosis I and Meiosis II. The DNA is only synthesized (replicated) once (prior to Meiosis I). The subdivision of meiosis are named like the subdivisions of mitosis (prophase, metaphase, anaphase, and telophase) but the events are somewhat different. One event that occurs in meiosis (specifically Prophase I) contributes to the genetic variation that is seen in the new developing cells. Crossing-over is the exchange of maternal and paternal genes as chromosome overlap and switch pieces of genetic material. As a result of crossing-over, all the gametes which are produced are genetically different from each other and contain pieces of both maternal and paternal genes.

One major difference between mitosis and meiosis is that meiosis results in a reduction in chromosome number as a result of a second cellular division. If cells divide correctly, each human gamete should contain 23 chromosomes

(haploid number). In males, four gametes (sperm) are produced as a result of meiosis. In females, four gametes

(eggs) are produced as a result of meiosis. Three of the four eggs that are produced are significantly smaller and will disintegrate; these are known as polar bodies. The one gamete which survives is known as the ovum, or egg.

Eventually this egg will be released in the hopes of being fertilized.

Recall, that as a result of normal meiosis in humans each gamete contains 23 chromosomes (haploid number (n)).

When gametes meet during fertilization, the gametes produce a human zygote with 46 chromosomes (diploid number (2n)). At times, cells may undergo nondisjunction ; this is the failure of homologous chromosomes to separate equally during meiosis. As a result of meiosis, gametes may be missing a chromosome or may contain an extra chromosome. For example, if a human gamete is fertilized that is missing a chromosome (22 vs. 23) the resulting offspring would have 45 chromosomes instead of 46 chromosomes. This condition is known as monosomy - ex. Turner’s syndrome. (Mono- meaning “one”) If a human gamete is fertilized that contains an extra chromosome (24 vs. 23) the resulting offspring would have 47 chromosomes instead of 46 chromosomes. This condition is known as a trisomy – ex. Down syndrome. (Tri- meaning “three”) These conditions are normally identified based on their location of the chromosome pair that is missing or contains an extra chromosome – Ex.

Trisomy 13, Trisomy 18, Trisomy 21. Nondisjunction is believed to increase with increasing maternal age.

The lily flower has six anthers (male portion) surrounding one carpel (female portion). Each anther has two pair of microsporangia (“pollen sacs”). It is in these microsporangia that you will observe the stages of meiosis. You will have to look at several different cells in each microsporangium to see exactly what is going on.


Diagram of Meiosis:


PART C: Observing Cell Division in Lily Microsporangia (Meiosis)

Overview Students will examine various slides illustrating the process of cellular division. They will identify and compare the various stages of meiosis


Access to Microscope

Microscope slides (Lily Microsporangia)

Lily Microsporangia–Meiosis

1.

Obtain a slide of the Lily Microsporangia. Place slide on the microscope and view under low power and then on medium power.

2.


Magnification: ______X

PART D: Using Pop beads to simulate the phases of Meiosis

Overview Students will simulate the phases of meiosis using pop beads.


40 Red pop beads/ 40 Yellow pop beads

2 Red centrioles /2 Yellow centrioles

4 Plastic tubular centrioles


Procedure –

1.

Construct your parent cell. Construct two strands of seven red pop beads and attach each strand to a red centromere. Repeat with two strands of seven yellow pop beads and a yellow centromere. Your beads should look similar to the illustrations below.

RED YELLOW a.

How many chromosomes does your parent cell have? _____ Is this number considered the diploid or haploid number? ______________________ b.

How many gametes are created as a result of a cell undergoing meiosis? ______ c.

How many chromosomes do you expect to find in each of the gametes that are formed at the conclusion of meiosis? _____ Is this number considered the diploid or haploid number?

______________________

2.

INTERPHASE: Just like in mitosis, this stage is the longest stage of the cell cycle and prepares the cell for division. Though the distinct chromosomes are not visible, the genetic material is undergoing an important process – DNA replication.

You can illustrate the chromosome duplication that occurs during interphase by constructing two chromosomes identical to the ones you made previously. Each half of the duplicated chromosome is called a chromatid. Join both red chromatids at the centromere to form a pair of sister chromatids. Repeat for the yellow chromosome. Place a pair of plastic centrioles, at ninety degree angles, just outside of your nuclear membrane. The centrioles also replicate during interphase so place each pair next to them in the cell. a.

Diagram Interphase as you have just simulated it above. Be sure to include the centrioles in your diagram. b.

What is the major event that occurs during interphase? ____________________


MEIOSIS I:

3.

PROPHASE I: During this phase we see the disappearance of the nuclear membrane, separation of centrioles to opposite poles and formation of spindle fibers. This phase is significant because we normally see crossing-over occur here. Crossing over occurs when arms of homologous chromosomes make contact and exchange portions between each other. Chromosomes align in the center of the nucleus and the arms of the chromosomes often intertwine. In some cases, the arms break off and reattach to the chromosomes with which they are entwined. This is important because it results in a redistribution of genetic material allowing for genetic variation in the cells produced. The diagram below illustrates crossing over.

Before Crossing Over  After Crossing Over has occurred

To simulate prophase 1, place the homologous chromosomes in the center of the with their arms entwined, snap three red beads off of one red chromatid and exchange them with three yellow beads from one yellow chromatid. Place the three yellow beads on the altered arm of the red chromatid. a.

Diagram prophase as you have just simulated it above. Be sure to illustrate crossing-over and to include the centrioles in your diagram. a.

What is the significance of Crossing-Over?


4.

METAPHASE I: Chromosomes disentangle and become aligned in the center of the cell in homologous pairs. Illustrate metaphase of mitosis by centering your chromosomes along an imaginary metaphase plate (center) with the centrioles still at opposite poles of the cell. . Think M etaphase =

M iddle! a.

Diagram Metaphase I as you have just simulated it above. Be sure to include the centrioles in your diagram.

5.

ANAPHASE I: Anaphase I is characterized by the homologous chromosomes separating and are drawn to opposite sides of the cell by spindle fibers. Think A naphase – Pulled A way. a.

Diagram Anaphase I as you have just simulated it above. Be sure to include the centrioles in your diagram.

6.

TELOPHASE I: During meiosis, cell division occurs and centrioles replicate, resulting in two daughter cells still containing paired chromatids.

7.

CYTOKINESIS: Separates the cytoplasm into two discrete daughter cells.

Illustrate the final stages of cellular division by moving each homologous pairs to the centrioles it was heading toward during anaphase. Imagine a cleavage furrow developing between each nuclei and separating the cell into two daughter cells. a.

Diagram Telophase I/ Cytokinesis as you have just simulated it above. Be sure to include the centrioles in your diagram.


8.

INTERPHASE II:

DNA replication DOES NOT occur during the second interphase stage of meiosis!

MEIOSIS II:

9.

PROPHASE II: During this phase the centrioles move to opposite poles of both daughter cells. The chromosomes move toward the center of the daughter cells.

Crossing – Over DOES NOT occur during the second Prophase stage of meiosis!

To simulate prophase II, move the centrioles to opposite poles of each daughter cell. Place the centromeres of the paired strands in the center of each daughter cell. a.

Diagram Prophase II as you have just simulated it above. Be sure to include the centrioles in your diagram.

10.

METAPHASE II: All the chromosomes line up, single file, in the center (equator) of the cell. Think

M etaphase = M iddle! Simulate Metaphase II by centering the paired strands along an imaginary line across the center of the cell. Line up the strands so they are centered in each daughter cell. a.

Diagram Metaphase II as you have just simulated it above. Be sure to include the centrioles in your diagram.


11.

ANAPHASE II: Anaphase II is characterized by the chromatids of each paired strand separating to their opposite poles of the cell. Each chromatid, with a well-defined centromere, is now a chromosome. Think

A naphase – Pulled A way. a.

Diagram Anaphase II as you have just simulated it above. Be sure to include the centrioles in your diagram.

12.

TELOPHASE II: Cell division is now completed resulting in four new haploid daughter cells. Each contains half of the chromosomes number of the original parent cell (haploid). (Female gametes = eggs,

Male gametes = sperm) A nuclear membrane forms around each cell’s chromosomes.

13.

CYTOKINESIS: Separates the cytoplasm into four daughter cells.

Illustrate the final stages of cellular division by moving each stands near its respective centrioles. Imagine a nuclear membrane around each chromosome and a complete division in the daughter cells from meiosis I, resulting in the four daughter cells. a.

Diagram Telophase I/ Cytokinesis as you have just simulated it above. b.

How does the number of cells produced during meiosis differ from mitosis? c.

How do the resulting cells compare to the original parent cell? d.

Females normally produce four gametes during meiosis (oogenesis) though only one is truly viable

(survive). Three of these gametes are smaller in size and disintegrate in the body; these are known as polar bodies. The one viable egg survives and is released in the hopes of being fertilized. Males, on the other hand, produce and keep all four of the sperm that are produced during their meiosis

(spermatogenesis). Why do you think this is?


Name: _________________________ Date: ________________________

POST-LAB QUESTIONS

1.

Describe what you see when viewing the slides of the onion root tip and whitefish blastula?

2.

Why do cells divide? What would happen if cells did not divide?

3.

________Which diagram most correctly represents the process of mitosis ? a.

b.

c.

4.

___________An organism’s diploid chromosome number is 16. At the end of mitosis each of this organism’s cells will have ____ chromosomes. a.

2 b.

4 c.

8 d.

16

5.

___________An organism’s diploid chromosome number is 16. At the end of meiosis each of this organism’s cells will have ____ chromosomes. a.

2 b.

4 c.

8 d.

16

6.

_______Using the diagram below, Place the cells in order from beginning to end of mitosis. a.

1, 2, 3, 4, 5 b.

2, 4, 3, 1, 5 c.

2,4,1,3,5 d.

1,4,5,2,3


7.

Briefly describe the events that occur in each of the following steps of the cell cycle:

Stage 1 : Interphase

Prophase

Stage 2: Mitosis Metaphase

Anaphase

Telophase

Stage 3 : Cytokinesis

8.

Explain a possible mechanism for the occurrence of monosomy (ex. Turners Syndrome)? Trisomy (ex.

Down Syndrome)?

9.

What is the advantage of crossing-over during meiosis?

10.

Complete the chart below comparing the process of mitosis to meiosis .

MITOSIS MEIOSIS

Purpose

Number of Division

(One/ Two)

Number or Cells Produced

(Two/ Four)

Are new cells produced gametes or somatic/ body cells?

New Cells Produced are Haploid or Diploid?

Does Crossing-Over Occur? If yes, during which phase?

(Yes/ No)

Are new cells genetically identical to parent cell or genetically different? (Hint: See above)


Lab 8. Cellular Division

RED YELLOW

MITOSIS MEIOSIS

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MITOSIS MEIOSIS

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