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AP Biology
Stem Cell Activity
Name_________________________________________
For this activity, you will work in groups of 3-4 to recreate the production of stem cells. You will
understand the difference between pluripotent, totipotent, and multipotent, and the difference
between a stem cell, blastula, morulla, and placenta.
Materials
4 different colors of Play-doh
Paper Clips
Paper Plates
Straws
Procedure
**For this activity, we will all work together. Write answers to the questions as we proceed.**
1. Building a zygote. Use a single color of Play-doh to make an egg (approximately the size of a pingpong ball) and a sperm cell (about the size of the period at the end of the sentence). Mix them
together to form the zygote (remember: the tail of the sperm falls off and does not actually enter
the egg). Place it on the Petri dish (paper plate) to represent in vitro fertilization.
2. Early cell divisions. Divide the single-celled zygote in half and reform into two spheres to represent
the two-cell stage. Divide each of these again to represent the four-cell stage. Repeat to represent
the eight-cell stage. Repeat once more to represent the 16-cell stage.
3. Morula. Push the 16 cells together to form a sphere (should look like Dippin’ Dots ice cream). This
will represent the morula stage of the cells. Set this aside on the Petri dish.
a. Totipotency. The 16 cells that make up the morula are considered totipotent, which means
that they can differentiate into any type of tissue whatsoever in the human body. *Note: it
is also at this stage that identical twins develop. The morula undergoes a mitotic event
before proceeding to differentiate.
4. Blastula. The steps so far have taken around 2 days to complete. The next stage, the blastula stage,
will occur between the 3rd and 14th day since fertilization. The first cells of the morulla to
differentiate (to decide on a tissue type and begin developing into this) are the cells that will form
the placenta.
a. Placenta. Pick a new color of Play-doh to represent the cells of the placenta. Make another
sphere the size of a ping-pong ball. Flatten this ball to form a large, thin bowl. This bowl will
represent the cross-section of the placenta. Use your straw to poke shallow holes all
throughout the placenta that will represent the cells of the placenta.
b. Placental implantation. Remove some of the cells of the morula. Build multiple smaller cells
(about the size of a pea) and place inside the placenta. These are the stem cells that are
growing inside the protected stem cell.
i. *Note: the entire morula is encased within the placenta, which in real life would
look like a hollow sphere. To make it easier for us to work with stem cells we have
cut our “placenta” in half.
c. Pluripotency. The cells that make up this entire structure represent the blastula. The cells
that make up the placenta have already undergone the “fate decision.” They will be
placental cells, and nothing else. The cells within the placenta are pluripotent, meaning they
can be ALMOST any type of cell. At this stage, the cells can form any type of tissue EXCEPT
the placenta.
d. Stem cell line. In a laboratory, this is the final step to harvesting stem cells. After developing
for 4-5 days in the blastula, the stem cells are transferred to a medium that will provide
necessary nutrients and environment for growth. The stem cells will maintain their
pluripotent characteristics as long as they are kept healthy and not directed to a specific
need. The blastula would at this point either be placed in a freezer to maintain the integrity
of the stem cells or be implanted into a female uterus to initiate in vitro pregnancy.
5. Gastrula. The gastrula begins development after the 14th day since fertilization. The purpose of the
gastrula is to develop into three separate embryonic tissue layers, or germ layers: the endoderm,
mesoderm and ectoderm. Development of the gastrula appears to be triggered when the placental
cells actually attach to the uterine wall.
a. Placenta. We will reuse our placenta for this activity, but remember that in real life the
placenta would either be forced to keep the stem cells intact OR begin development of
embryonic tissue layers—not both.
b. Endoderm. Remove or make another cell of the same original color as your morula. The cells
at this point would be approximately the size of a pea, so reshape/mold to get to this size.
c. Mesoderm. Remove a piece of a new color not yet used and mold it into the size of a
marble. Flatten this piece into a thin layer—thin enough that it would surround your
endoderm cell. Carefully fold your mesoderm layer over your endoderm layer WITHOUT
MIXING THE COLORS.
d. Ectoderm. With the fourth unique color, mold the play-doh into the size of a ping pong ball.
Flatten this piece into a thin layer and wrap around your mesoderm, which at this point
should be wrapped around your endoderm. Again, DO NOT MIX THE COLORS
e. Germ layers. Fold the end of your paper clip and carefully slice through the Play-doh to
reveal the cross section of your gastrula cells.
f. Multipotency. The gastrula layers are now multipotent. They are still not fully decided what
tissues they will form, but they have made a fate decision to be a specific category.
i. Inner layer, Endoderm. The endoderm will develop into the digestive and
respiratory systems.
ii. Middle layer, Mesoderm. The mesoderm will develop into the bones, blood cells,
and heart.
iii. Outer layer, Ectoderm. The ectoderm will develop into the skin and central nervous
system (brain, spinal cord and nerves).
6. Adult stem cells. At this point, the embryonic layers are considered “adult” stem cells. The placental
cells are still only able to become placental cells. No totipotent stem cells remain.
Table 1 (Fill out while performing the steps of the activity)
Totipotent Stem Cells
Zygote
Diagrams of
Play-Doh
Creations
Pluripotent Stem Cells
Multipotent Stem Cells
Blastula/Blastocyst
Gastrula
Label placenta and early
embryo
Label placenta and three
tissue layers
Totipotent
Pluripotent
Multipotent
Zygote
Blastula/Blastocyst
Gastrula
Morula
Embryonic stem cell
Germ Layer
Morula
Approximate days
cell division
occurs
Approximate
number of cells
Definition of
important terms
Post-Lab Questions
1. What is the major difference between embryonic and adult stem cells?
2. How do the following terms apply to stem cells?
a. Self-renewing
b. Differentiated
3. Predict how this process can be used to impregnate women through in vitro fertilization.
4. Why do stem cells have to be harvested so early in the embryo’s life? How does this relate to
the controversy behind stem cells?
5. What is the difference between embryonic stem cells and stem cells taken from bone marrow or
the umbilical cord?