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