Lab Exercise 6

MITOSIS
Introduction
Cells divide to increase in number. A single cell divides into two: these two cells will each divide
into two cells, and so on and so forth. In time, millions of cells are produced. Mitosis is the division of
nuclear material in which each new nucleus obtains the same number of chromosomes and the same
nuclear code as the original nucleus. Mitosis occurs in four phases: prophase, metaphase, anaphase, and
telophase. After telophase and before the next mitosis, there is the interphase, which is not a stage of
mitosis, but a part of the cell cycle (interphase+mitosis). In a 24-hour cell cycle, a cell undergoes mitosis
for about one hour and stays at interphase for 23 hours.

Objectives
After this exercise, the students should be able to:
1. Locate cells in the whitefish blastula or onion root tip that are in the process of dividing by
mitosis.
2. Identify cells in the interphase stage and those undergoing the different stages of mitosis.
3. Describe the changes that occur in the cell as it undergoes mitosis.

Materials
compound microscope

prepared slide of the whitefish blastula or onion root tip (longitudinal section)

Procedure
1. Using the low-power objective of the microscope, locate the different cells undergoing mitosis,
then switch to high-power objective.
2. Look for cells that appear to be in the different stages of cell division.
3. While going through the different stages, identify and write the stage of mitosis where the
following observations are made.

a. –cell with very visible nucleus and nucleolus; the chromosomes appear as
fine dots within the nucleus

b. –cell nucleus enlarged; nucleolus no longer very visible; chromosomes

appear like short strands inside the nucleus

c. –chromosomes appear as long and thin strands lined up along the center or
equator of the cell plate (whitefish blastula)

d. –two sets of separate chromosomes are seen and seemingly trying to pull
each other apart

e. –chromosomes are now at opposite ends of the cell; middle part of the cell
seems to have a line across the center that almost divides it into two cells

f. –product of the division; appears as cells in interphase but smaller and side
by side; actually, the start of new interphase
Results
A. Draw the different stages of mitosis in the boxes.

Interphase Prophase Metaphase

Anaphase Telophase
B. Answer the following questions.
1. How does mitosis help an organism grow?

2. Is the root tip an ideal specimen for observing the phases of mitosis? Why?
3. What are the spindle fibers made of?

4. What is the phase in which each of the following occurs?

alignment of the chromosomes at the equator
disappearance of the nuclear membrane
formation of the cell plate
formation of two daughter cells
separation of sister chromatids and their movement toward opposite poles

5. How many chromosomes will each cell receive in telophase if each onion cell has 16
chromosomes?
 Lab Exercise 7
TIME INVOLVED IN MITOSIS
In this activity, determine whether all the stages in mitosis require the same in different amount of
time to complete the process. This is done by counting the number of onion root tip cells in the four
stages of mitosis and those in interphase.
Objectives
After this exercise, the students should be able to:
1. Count the number of cells in each of the different stages of mitosis and interphase
2. Compute the length of time in minutes needed to complete each stage
Materials
Microscope
Prepared slides of onion root tip (Allium), longitudinal section

Procedure
I. Locating and Counting the Cells in the Different Stages of Mitosis
1. Locate the part in the longitudinal section of the root the area with cells that are
undergoing mitosis. This is usually found along the region of cell division. After locating
the cells under LPO, switch to HPO.

2. Count and record the number of cells under each stage in the table on the next page.
Include all the cells in the field of view.

3. Move the slide to be able to navigate into another area where cells are also dividing.
Again, count the cells under each stage of mitosis and those under interphase.

4. Repeat Step 3 for third new area.

5. Add all the number of cells counted in each phase and interphase for the three areas.
Record the figures in Table 1 under the column marked “total number of cells in each
phases”.

II. Determining the Time Spent Under Each Stage

In this part, assume that the number of cells in a specific stage is an indication of the time
spent in that stage during mitosis. The time spent in a mitotic stage and in interphase can be
calculated if the total time for mitosis is known. Onion cells usually require 12 hours or (720 minutes)
to complete the cell cycle (from interphase to interphase). Therefore, the amount of time needed can
be calculated using this formula:
Time for stage (i.e., prophase)=number of cells counted (prophase) x720mins
Total number of cells counted

Results
A. Tabulate the findings.
Stage Area 1 Area 2 Area 3 Total Number Time in
of cells in each minutes
phase
Interphase

Prophase
Metaphase
Anaphase
 Telophase
Total
Results after counting the cells in each stage of mitosis and interphase
B. From the above tabulation, answer the following questions.
1. Which stage requires the longest time to complete?

2. Which stage requires the next longest time to complete?

3. Which stage requires the shortest time to complete?

4. What is the reason for the answer in question number 1?

 Lab Exercise 8
GENETICS
Introduction
Genetics is the science that explains the variation and transmission of inherited characteristics
from parents to offspring. The basic laws of heredity became popular to science in 1865, with the
publication of the works of Gregor Mendel, the father of genetics. He observed that by breeding pairs of
different varieties of peas, the offspring resembled one of the parents. This inspired him to continue his
work that resulted to more experiments on plants.
Before starting this exercise, read the discussion that comes before this activity. Knowledge of
how genes separate and recombine when chromosomes undergo meiosis is basic to the understanding of
heredity.

Objective
After this exercise, the students should be able to:
1. Understand the mechanisms of heredity and explain the variation that exists among
parents and the offspring

Procedure

1. Determine which of the following traits are dominant and which are recessive by making
a statistical survey of the following traits in the class.

Traits Number of Students Proportion

Attached earlobes
Unattached earlobes
Right-handed
Left-handed
Ability to roll tongue
Inability to roll tongue
Curly hair
Straight hair
With 10 fingers
With 11-12 fingers

2. Solve the following problem.

In fruit flies, gray is dominant over black. If a pure bred gray fruit fly crosses with a black
fruit fly, what percent of the offspring will be gray?

3. The law of probability states that the chance (or probability) of the simultaneous
occurrence of two or more independent events is equal to the product of the probabilities
that each will occur separately. Thus, when a coin is tossed in the air, and allowed to land,
it will most likely land as “head” or “tail” of which the probability of head or tail is one in
two, or one half in either case. Obtain a one-peso coin and toss it in the air 100 times.
Record the results in the table below.
Class Tally Total

Heads

Tails

Total
 a. For the first 10 tosses, did the number of tosses result in exactly ½ heads and ½
tails?

b. Is the ratio of ½ heads and ½ tails closer in 100 tosses or in 10 tosses? Why?

Results
Answer the following questions.
1. Did all the traits mentioned in the table occur in the class? How come?

2. Explain the overall ratio from the different traits surveyed in the class.

3. What are the dominant traits? What are the recessive traits?

4. How is it that the coin came up as “heads” about the same number of times it came up as
“tails?”

5. As you are using it, what does the word “chance” mean?
 Lab Exercise 9
REPRODUCTION IN ANIMALS

Introduction
Reproduction is one of the basic biological properties of life. There are two ways by which
organisms reproduce. One is through the asexual method. In this process, there is no genetic variation in
the offspring since fusion of the gametes does not occur. This type is very common among unicellular and
lower forms of animals. In some, a small outgrowth, often a bud, develops along one side of the body.
Once this bud matures, it can detach and become another individual. The second type of reproduction is
sexual. This process involves the fusion of the egg cell and the sperm cell. This method of reproduction is
found in almost all members of the animal kingdom, from the poriferans to the chordates. In some lower
forms of organisms, like the protists, both the sexual and asexual types occur. This is especially true to the
paramecia that can undergo transverse fission and, at the same time, conjugation.

Objective
After this exercise, the students should be able to:

1. Examine and differentiate the various methods of reproduction in animals

Materials

Compound microscope
Prepared slides of Paramecium (conjugating and undergoing transverse fission), hydra, sponges,
sporozoan (Plasmodium)
chart (if available)

Procedure
I. Asexual Method of Reproduction
1. Budding: Borrow the prepared slide of hydra and look for the presence of a small lateral
outgrowth resembling a young hydra. This is a bud. In budding, a new individual arises
from the parent as an outgrowth, then will later on detach and grow into an adult with
characteristics that are very similar to the parent.

2. Fission: Borrow the prepared slide of Paramecia undergoing fission. Observe that the
direction of the division is transverse (although it may also be longitudinal). The
organism divides equally into two along the middle part, with each growing to the
original form. The division starts at the nuclear level, followed by the constriction of the
cytosome. Cytoplasmic organelles form during this period. This is followed by the
complete division of the cytoplasm into two cells, each with a complete set of organelles
like that of the parent.
3. Sporulation: Borrow the prepared slide of Plasmodium showing sporulation, where a
nucleus is undergoing multiple divisions. If slides are not available, get a chart
illustrating the life cycle of Plasmodium vivax, a malarial parasite. This chart will
describe how the process takes place. Refer to the chart in making diagrams of the
different stages of sporulation.

II. Sexual Method of Reproduction

This method is very common in higher forms of animals, like humans. Variations may
occur with different groups of animals; however, the essential features are the same such as the
growth and development of the male and female gametes, the union of the sex cells, and the
formation of the zygote. In lower forms of animals, the processes are simpler. Borrow the slide of
conjugating Paramecium in order to see how it differs from a Paramecium undergoing binary
fission, an asexual method.
Results
I. Draw the observations under the microscope.
A. Asexual reproduction

A budding Hydra

Paramecium undergoing fission

 Sporulation in Plasmodium vivax

B. Sexual reproduction

Conjugating Paramecia

II. Answer the following questions.

1. How is budding in hydra similar to budding in plants?

2. Is the fission in Paramecium transverse or longitudinal? Why? How many new individuals
are formed after the process? Can this be compared to mitosis?
3. Of the three types of asexual reproduction mentioned, which is more likely to result in faster
and more cell production? Why?

4. Which is more complex-the asexual or sexual type of reproduction? Why?