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
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