Download Animal Development Lab

Name: ________________________________________________________ Period: ________
Animal Development Lab
Most animals develop from a single fertilized egg (zygote). How does a zygote develop into
the many different kinds of cells that make up the entire animal? This question can be answered by
studying the process of embryological development. In this lab, you will observe the various stages of
embryological development in the starfish using the following website:
http://science.jburroughs.org/resources/SeaStarembryology/starfishembryology.html (good labeled
pics) or
http://www.discoverdevelopment.com/PHP/SlidesStarfish.php
Starfish belong to a group of organisms called Echinoderms (ee-kine’-o-derms). Their development is
very much like that of humans, and they belong to a branch of the Kingdom Animalia called
deuterostomes, as do all primates (humans are primates). Deuterostomes are distinguished by how
their embryos develop; in deuterostomes, the first opening (the blastopore) becomes the anus, while in
protostomes (simpler animals) it becomes the mouth.
After fertilization by a single sperm, the egg is fertilized and is now known as a zygote. This zygote
then divides into two cells by the process of mitosis. This new two-celled organism is now referred to
as an embryo:
egg
zygote
embryo
Obtain fertilized polar bodies, find a zygote under 400X magnification. Being careful to draw to
scale, sketch the zygote here, using the appropriate colors if you have colored pencils.
Following the division into two cells that continue to be joined together, the embryo further divides
into four cells:
1
2 cells
4 cells
Obtain Arbacia Early Cleavage slide. Find the four celled stage and sketch under 400X here. In
addition, be sure that the scale is correct.
The embryo continues to divide, going from four cells to eight cells.
4 cells
eight cells
The embryo continues to divide by the process of mitosis. After many cell divisions, the embryo
appears as a hollow ball of cells. This hollow ball is called the blastula.
blastula
Obtain a blastula slide. Observe and sketch under 400X.
Estimate the number of cells in this embryo: ______________
2
How does the size of these cells compare with the size of the original zygote?
At this point in the embryo’s development, all cells are nearly the same. They have not yet begun the
process of differentiation that will result in cells specializing to carry out different functions.
Once the hollow ball of cells (called the ____________________________) is complete, some of its
cells begin to move, or migrate, in a very precise way. The beginning of this movement can be seen in
the image below, and is called the blastopore.
blastopore
Some cells move towards the interior of the ball of cells, and this stage is called the gastrula.
The blastopore is much larger now, and some cells that were on the outside of the embryo are now on
the inside.
blastopore
Obtain a gastrula slide. Observe under 400X and sketch it here:
The outer layer of this form is called the ectoderm, and develops into the skin and nervous system of
the animal. Label this layer on your sketch.
The inner layer of this form is called the endoderm, and develops into the lining of the digestive tract
and organs that are part of the digestive process. Label this layer on your sketch.
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In many animals, like humans, a third layer of cells forms between the outer and inner layer. This layer
is called the mesoderm and develops into the muscles, circulatory system, excretory system, and in
some animals, the respiratory system. In deuterostomes the mesoderm forms as evaginations of the
developed gut that pinch off, forming the coelom (sea’-lum). The coelem is a body cavity, and will be
completely lined with mesoderm in the embryo.
Starfish larval forms are called bipinnaria. They are significantly more developed than the previous
stages. They move using cilia, and you can see a mouth, a digestive system, and an anus. This larva
will metamorphose into an adult starfish.
Obtain a bipinnaria slide. Observe under 400X and sketch the larva here:
You have observed many stages of starfish embryo development. How does cell size change from the
zygote to the larval forms?
Observe the drawing of a blastula below. What might happen to the adult starfish that grows from this
blastula if the cell marked A was destroyed at the blastula stage?
A
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All animals begin life as a single fertilized egg, yet they grow to become a complex organism
consisting of billions of cells. Yet, even though every cell in an organism contains the same DNA, not
all cells are the same. Keeping in mind that all cell activities are controlled by DNA, suggest a reason
that different types of cells are different, even though they have the same DNA.
Using knowledge from cell division concept, would you expect the MPF (mitosis promoting factor)
activity to fluctuate or remain steady during cleavage?
How does an egg cell prevent polyspermy?
Number the stages of development in the correct order: gastrula, morula, zygote, blastula
If some of the cells in the ectoderm are mutated, what organs could be affected?
What role does apoptosis play in embryo development?
Why can’t nerve cells be grown from muscle cells?
How do maternal or cytoplasmic determinants allow for differential cellular development?
How can cells be induced to develop by other nearby cells?
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