Modeling Early Embryology & Stem Cell Concepts

By Chowning, Jeanne Ting; Griswold, Joan et al. | The American Biology Teacher, February 2008 | Go to article overview

Modeling Early Embryology & Stem Cell Concepts


Chowning, Jeanne Ting, Griswold, Joan, Mathwig, Jodie, Massey, Dianne, The American Biology Teacher


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Stem cells self-renew and also have the potential to give rise to daughter cells that can differentiate into many types of cells. In this activity, students make play dough models of early embryonic development. These models help visualize where embryonic stem cells come from and how their potential to develop into different types of cells changes over time. Student handouts to accompany this activity (which is part of a larger stem cell curriculum) can be found at http://www.nwabr.org/education/ stemcell.html.

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Materials

* four different colors of play dough

* paper plates to represent Petri dishes

* paper clips

* straws

Procedure

Demonstrate the steps as students make their own models.

zygote (Figure 1)

Use a single color to make both an egg (the size of a ping pong ball) and a much smaller sperm cell. Mix them together to form a zygote on a "Petri dish," representing in vitro fertilization. The "tail" of the sperm drops off and does not enter the egg.

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Early Cell Divisions

Divide the zygote in half, making two spheres. Divide each of those two cells in half, then each of those in half again, until there are 16 cells.

Morula (Figure 2)

Push the 16 cells together to form a sphere (morula). Through this stage, the cells are considered totipotent--if separated, any one of them could become a complete individual.

Blastula (Figure 3)

The blastula stage occurs 3-14 days after fertilization. The mammalian blastula is often referred to as a blastocyst. Pick a new color, make a sphere the size of a ping pong ball, then flatten the ball into a bowl. The bowl represents pre-placental cells. In real life, they form a hollow ball; the bowl represents a cut-away view (see Figure 3). Use the end of a straw to make indentations that look like cells.

Make pea-sized spheres to represent the cells growing inside the hollow ball. These are the cells of the inner mass ("embryonic stem cells"). The cells have already gone through one "fate decision." The cells that make the hollow ball can only become placenta. The cells of the inner mass are pluripotent; they can become any type of cell in the body except placenta.

At this point, an embryonic stem cell line could be made by transferring cells from the inner cell mass to a culture dish and growing them in a medium that provides support and nutrients.

Gastrula (Figure 4)

Make a new early placental bowl in the same color as the previous one. …

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