Exercise # 2: Cells and Cell Division

Group 1: Cruz, Earl. Inson, Noe. Ramos, Franklin. Talino, Marianne. Tanjuatco, Luis

Date submitted: Dec. 1, 2011

Introduction

More than three hundred years ago,

after the invention and developments of the

microscope, scientists began studying cells.

In the year 1665, after observing slices or

pieces of cork under the microscope, Robert

Hooke reported that: "These pores or cells,

were not very deep, but consisted of a great

many little boxes, separated out of one

continued long pore, by certain

diaphragms." He thus discovered the cells.

However, it was only about one hundred

years later when the study of cells became

very important. By that time, many scientists

claimed that cells were indeed the building

blocks of living tissue.

In 1883, an English Botanist named

Robert Brown discovered the nucleus of

plant cells. Five years later, Matthias Jakob

Schleiden claimed that all plant tissues are

composed of cells and the embryonic plant

came from a single cell. A year later,

Theodor Schwann claimed that all animal

tissues are composed of cells; he also

claimed that plant and animal cells were

fundamentally different in structure.

In 1840, Albrecht von Roelliker

discovered what we now know as gametes.

He claimed that the sperm and egg (cells)

are also cells. Another five years later, Carl

Heinrich Braun claimed that cells are the

basic units of life. Ten years later, after

studying Robert Brown’s nuclei discovery,

Rudolf Virchow completed the cell theory

by concluding that all cells come from

preexisting cells.

“Omnis cellula e cellula.” According to

Rudolf Virchow, all cells come from

preexisting cells, how come he concluded

this? The answer is the phenomenon of cell

division, mitosis and meiosis. In general,

cell division is divided unto two main parts,

karyokinesis or mitosis (nuclear division)

and cytokinesis (cytoplasmic division).

Mitosis is basically the reproduction or

formation of body cells or somatic cells. It is

also a way of distributing the chromosomes

and the DNA that a “parent cell” contains to

continuing cell generations. However, this is

not the only function of mitosis. Mitosis also

functions as a rejuvenating process for cells

or tissues, because through mitosis damaged

and old cells are replaced by healthy and

new cells (Hickman et al. 2011).

Mitosis is further divided unto five

important processes or parts. First is

interphase, it is in this stage where DNA

replication occurs. Every DNA molecule

replicates and new partners are synthesized

for each strand making two identical DNA

molecules produced from the original strand

of DNA molecule. Next stage is Prophase.

In this stage, the nuclear membrane or

envelope starts to disappear, two

centrosomes move to opposite poles,

chromatin condenses and forms visible

chromosomes and spindle fibers start to

appear. After Prophase is Metaphase. In this

stage, the condensed sister chromatids align

at the metaphase plate or middle of the cell.

By this process, it prepares itself to separate

in the next stage. Next is Anaphase. In this

stage, the cohesin proteins that held the

sister chromatids are removed making them

two separate chromosomes. The independent

chromosomes then move toward opposite

poles. Once the two chromosomes reach

their poles, Telophase begins. In this last

stage of Mitosis, spindle fibers disappear

and the nuclear envelopes start to form

around the separate two daughter nuclei

(Animalgenome.org).

After the division of the nucleus, the

cytoplasm divides this process is called

cytokinesis. In this stage, a cleavage furrow

appears between the two independent nuclei.

It deepens and pinches until the cytoplasm

separates and forms two daughter cells.

On the other hand, meiosis is the

reproduction or formation of gametes or sex

cells. Basically, the process of mitosis and

meiosis are similar. However, meiosis will

undergo mitosis twice. Thus, the process

forms four daughter cells. But, this

formation of four cells only applies to sperm

cells. Egg cells on the other hand, lose the 3

daughter cells since they become polar

bodies that could later be recycled in

meiosis, therefore, only 1 egg cell is formed.

Materials and Methodology

As Biology Lab class started,

handouts were given by the lab assistant to

be used for the day’s session. To be done for

the day were the observation of the of the

stages of both meiosis and mitosis,

observing the cellular respiration.

For the observation and

identification of meiosis and mitosis that

was done, a microscope was taken by each

student or group, (depending on their

preference,), each one having their assigned

microscopes, which would all be found at

the far end of the room.

For the identification of the stages

of mitosis, a prepared slide of whitefish

blastula was used. The slide was examined

under the LPO. Under this magnification,

we located an area with the appropriate cell

spreading, an area where cells wouldn’t

overlap each other and as a result, each cell

were clearly viewed. After being able to find

an area with the said appropriate cell spacing

or spreading, the HPO maginification was

used by our group to have a closer look at

the different stages of the cells. The different

stages that were found in the slide with the

use of the microscope were then drawn into

the handouts.

On the other hand, for the

observation of the different parts of meiosis,

a prepared slide of mouse testis was used.

Much like what our group has done in the

observation and identification of the parts of

mitosis, same procedures were done as to

finding and locating the cells that were

needed to be observed.

Results and Discussion

A. Observing Protozoans

1. What are the different organisms that you

have seen? Describe the major locomotory

organs of each.

The first organism is the Euglena. It has

flagella which looks like a cilia but longer

and is only few compared to cilia. The next

organism is called Foraminifera. It has

Figure 1: Euglena

Figure 2: Foraminifera

Figure 3: Plasmodium

Figure 4: Trophozoite

pseudopods, which are just temporary

projections of eukaryotic cells. Next is

Plasmodium. It has no locomotory organ.

Finally, there is the Trophozoite. It has cilia

as its locomotory organ which is composed

of many whip like appendages.

B. Observing the animal cell from

multicellular organism

1. What part of the cell became visible

after the addition of the stain?

The nucleus, cytoplasm and the

plasma membrane became visible.

2. What is/are the function of these

parts of the cell?

The nucleus processes genetic

information. The cytoplasm holds

the organelles in place and acts as

their medium of suspension. The

plasma membrane allows molecules

and ions to pass in and out of the

cell.

3. Do you think that Robert Hooke was

correct in giving the name “cell”

(small rooms) to the specimen he

saw in the cork? Support your

answer.

Robert Hooke was correct. Cells

definitely look like small rooms

filled with organelles. Like rooms,

cells are enclosed with walls called

plasma membrane. Like a room, it

has a ‘door’; just like how

transporters function to allow

molecules and ions to pass in and

out of the cell.

4. Do you think Robert Browne was

right when he gave the name

“nucleus” to the “nut-like” part he

saw inside the cell? Support your

answer.

A nucleus definitely looks like a nut

in such a way that it is almost

circular in shape. Furthermore, like

a nut, it has a covering called the

nuclear envelope, which is a double

membrane.

Figure 5: Unstained Cheek Cell (100x)

Figure 6: Stained Cheek Cell (400x)

5. Do you see a darker stained part

inside the nucleus?

Yes, that part is called the nucleolus.

6. What organelles did you see in the

specimen?

Under the microscope, there are

only three things that are visible:

nucleus, cytoplasm and plasma

membrane.

7. How do stains facilitate the study of

cells?

Stains give a clearer picture of a

specimen. It enhances the image

highlight some certain cellular

components.

C. Recognizing the different mitotic

stages

‘

Figure 11: Telophase

1. A large spherical nucleus, with the

nuclear membrane intact, grainlike

chromosomes and one to two

nucleoli. This is the stage of

interphase.

2. A large, spherical nucleus with a

nucleolus and nuclear membrane Figure 8: Prophase

Figure 7: Interphase

Figure 9: Metaphase

Figure 10: Anaphase

Figure 8: Prophase

intact and with thickened, more

distinctly ribbon-like chromosomes.

The chromosomes may look like a

dish of spaghetti. This is the stage of

interphase-Gap 2.

3. A cell in which the chromosomes

appear as a loose knot in the center

of the cell. The nuclear membrane,

if still present, is indistinct. The

nucleolus may start to fade. This is

the stage of prophase.

4. A cell in which the chromosomes

are aligned in the equatorial plane of

the cell. This is the stage of

metaphase.

5. A cell in which the chromatids are

moving to opposite poles of the cell.

This is the stage of anaphase.

6. A cell in which the chromatids,

though fairly distinct are close to the

opposite poles of the cell. A cell

plate may be forming at the middle

of the cell. This is the stage of

telophase.

7. Look for two cells that appear to

have finished dividing recently.

These are the daughter cells and the

stage seen is the stage of

cytokinesis.

D. Determination of Duration of Mitotic

Stages

Total number of cells in the field=71Total number of cells(71) – Total number of mitotic figures(20) = Total number in interphase(51)Duration of stage(percentage) = (number of cells in a stage / total number of cells) x 100Duration of stage(h and mins) =(number of cells in a stage / total number of cells) x 1440Error% = (Actual Percentage-Theoretical Percentage) / Actual Percentage

Table 1. Determination of duration of mitotic stages.

Mitotic Stage

Number of CellsField 1 Field 2 Field 3

Interphase 16 14 21Prophase 4 5 3

Metaphase 3 1 2Anaphase 0 0 1Telophase 0 1 0

Total 23 21 27

Total Percentage (%)

Duration (h and mins)

% Error

51 71.83% 17h 14mins

-25.30%

12 16.90% 4h 3mins 82.25%6 8.45% 2h 2mins 52.66%1 1.41% 20mins 29.08%1 1.41% 20mins -41.84%71 100% 23h

59mins

Figure 13: Field 1

Figure 15: Field 3

a. What stage has the longest duration?

Why?

Prophase. It is because the nucleolus and the

nuclear envelope is just starting to disappear

and the mitotic spindle is beginning to

lengthen. The centrosomes are starting to

move away from each other.

E. Meiosis Stages

(Note: The different Meiosis stages weren’t

labeled because of the scarcity of clear

pictures on the Mouse Testis)

Mitosis and Meiosis differ in such a way

that Meiosis involves crossing over of

homologous chromosomes. These

homologous chromosomes will undergo

almost the same division as mitosis.

However, the end product of Meiosis I

would be 2 haploid daughter cells. These

daughter cells will undergo another division

called Meiosis II. The division is also

similar to Mitosis except it will yield 4

haploid daughter cells.

Figure 12: Mouse Testis (LPO)

Figure 12: Whitefish Blastula

Figure 14: Field 2

F. Comparison of Mitosis and Meiosis

Distinctive

Features

Mitosis Meiosis

Chromosome number of parent cell

46 46

Number of DNA

Replications1 2

Number of cytoplasmic

divisions1 2

Number of daughter

cells produced

24

Chromosome number of

daughter cells

46 23

Site of cell division

Somatic cells

Gametes

Purpose Cellular reproduction and general growth and repair of the

body

Sexual reproduction

G. Error Analysis: Site a potential error

that you may have encountered in you

experiment. Explain.

Some stages cannot be determined properly

because of the blurry parts in the image.

There could be that possibility of

misidentification and miscalculation.

1. During what stage of the cell cycle

is the nuclear material doubled?

Interphase – Synthesis phase

2. Are the stages of mitosis occurring

simultaneously?

No, because it has to wait for one

stage to completely finish until the

next stage can begin.

3. In what material is the coded

information of the cell stored?

The genetic information/DNA can

be found in the chromosomes

4. What should be the chromosome

number in daughter nuclei formed

by mitotic division of cells having

the following chromosome

numbers?

16 __16__ 68 __68___

22 __22___ 8 ___8___

5. Explain why the catfish blastula is

selected for the study of mitosis.

It is because it is the stage where

most mitotic activity happens.

6. Based on the obtained data in the

table, what can you infer about the

relative length of time that each

stage spend in order for mitosis to

be completed?

Since mitosis is cell division,

necessary preparations have to be

made. Prophase, which is the first

stage of mitosis, basically finalizes

the preparation of the cell when the

nucleolus and nuclear membrane

disappear and centrosomes start to

part from each other. Next is

metaphase, which basically involves

the aligning of chromosomes in the

middle of the cell forming the

metaphase plate. Anaphase, which

only took about 20 minutes, involve

the pulling of chromosomes towards

opposite poles. Finally, Telophase,

which also took only a number of

minutes, basically involves the

forming of the cleavage furrow and

the reappearance of the various parts

of the cell.

7. List three major differences between

the events of mitosis and meiosis.

Meiosis has 4 haploid daughter cells

while mitosis has 2 diploid daughter

cells. Meiosis has 2 cytoplasmic

divisions while mitosis has only 1.

Meiosis involves crossing over of

traits while mitosis does not.

8. How are Meiosis I and Meiosis II

different?

Meiosis I produces 2 haploid

daughter cells while Meiosis II

produces 4 haploid daughter cells.

9. How do spermatogenesis and

oogenesis differ?

Each daughter cell in

spermatogenesis develops into a

sperm. In oogenesis, one daughter

cell becomes the ovum while the

three polar bodies die.

10. Why is meiosis important for sexual

reproduction?

It is important because it is able to

make 4 daughter cells wherein the

chromosomes split and crosses over

for the interchanging of genetic

information each daughter cell is

different. It allows variation of

characteristics in every generation.

Literature Cited

Baker R, Vanhoeck. 2004. Cell Cycle Duration. http://www.newton.dep.anl.gov/askasci/mole00/mole00550.htm. Accessed 1 Dec 2011.

Dillon, Mary. 19 Oct 2008. Spermatogenesis vs. Oogenesis. http://campus.udayton.edu/~INSS/Dillon230/LECTHELP-2/2spermatogenesis_vs.htm. Accessed 30 Nov 2011.

DOMIX Studio. n.d. Pseudopod. http://en.mimi.hu/biology/pseudopod.html. Accessed 30 Nov 2011.

Goldsworthy, Traci. March 2009. Whitefish Blastula - Mitosis stages. http://goldsworthybiology.blogspot.com/2008/07/whitefish-blastula-mitosis-stages.html. Accessed 30 Nov 2011.

Hinterthuer, Burnetta. n.d. The Cell Cycle and Mitosis. http://faculty.nwacc.edu/bhintert/documents/TheCellCycleandMitosis.pdf. Accessed 30 Nov 2011.

Kimball, John. 24 April 2011. Cilia and Flagella. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Cilia.html. Accessed 30 Nov 2011.

Laboratory handout. 2011. Exercise # 2: Animal Cells and Cell Division. Bi 101.1 Laboratory Handout. Ateneo de Manila University, Philippines.

The NAGRP Bioinformatics Project Team. n.d. Meiosis vs. Mitosis. http://www.animalgenome.org/edu/genetics/mitosis.html. Accessed 30 Nov 2011.

Nair, Sonia. 22 Sept 2011. Cytoplasm Function in a Cell. http://www.buzzle.com/articles/cytoplasm-function-in-a-cell.html. Accessed 30 Nov 2011.

Simmons, Kent. 2007. Cell Theory. http://kentsimmons.uwinnipeg.ca/cm1504/celltheory.htm. Accessed 30 Nov 2011.

Smith. 2001. Discovery of Cells and the Development of Cell Theory. http://www.smithlifescience.com/celltheory.htm. Accessed 30 Nov 2011.