Download embryology lab 2015

Lab Activity: Embryonic Development in Starfish
Purpose: To observe stages of development in a starfish embryo.
Background: Embryo Development Reference: (Use to help label your pictures and for conclusion)
In multicellular organisms that reproduce sexually, fertilization of the egg by the sperm produces the
zygote, which marks the beginning of the new individual. During the period of development of the singlecelled zygote until the hatching or birth of the multicellular individual, the new organism is referred to as
the embryo. The study of the development of the embryo is called embryology.
The fertilized egg can be distinguished by the presence of a fertilization membrane surrounding the cell.
Also, the nucleus in a fertilized egg is quite indistinct, if seen at all, and the nucleolus has disappeared. Soon
after fertilization, the zygote begins cleavage. This process consists of successive cell divisions, in vertical
and horizontal planes, so that each division doubles the previous number of cells.
After a few such divisions, the embryo consists of a ball of many cells. At first, the cells are clustered
together without any distinct space or cavity between them, and the embryo somewhat resembles a
mulberry. It is therefore called the morula (Latin morum = mulberry).
In most cases, however, the cells soon rearrange themselves to form a definite ball around a central cavity.
This spherical, hollow ball of cells is called the blastula, and its central cavity the blastocoel.
Further development of the blastula results in the formation of a gastrula, a stage characterized by the
appearance within the embryo of a tubular or sac-like structure called the archenteron (= primitive gut). As
the name suggests, this tube is destined to become the digestive tract. At this early stage, the archenteron
has only one opening to the outside, which is called the blastopore.
The process of formation of the gastrula is called gastrulation. Gastrulation is accomplished by the pushing
in of cells from one end of the blastula. It may be likened to the pushing in of an inflated balloon from one
end with your finger. However, in the embryo, cells migrate from the outside to the interior.
Because of the formation of the archenteron, the embryo now consists of two walls. The outside wall,
which was also present in the blastula, is now called the ectoderm; the wall of the archenteron, which is in
the interior, is called the endoderm. The space between the two is what remains of the original blastocoel.
In the majority of animals a third layer of cells now arises and occupies much of the space between the
ectoderm and the endoderm (thus further reducing, or in some cases even completely obliterating, the
blastocoel). This middle layer is called the mesoderm.
The ectoderm, endoderm and mesoderm are called the primary germinal layers. Once these layers are
established, tissue differentiation and organ formation proceed rapidly so as to give the embryo its
characteristic shape and form. The primary germinal layers are specialized in that each of them has the
potential to give rise to only certain specific structures.
Materials: Prepared slides of starfish embryology, compound microscopes
Procedure:
The prepared slides provided show the different stages in starfish development from the unfertilized egg to
the early larval stage. The material has been stained for increased clarity.
Using the reference pictures below, your task is to determine the stage of development for each unknown
slide. Yes, the lab tech messed up the labeling and you need to fix it.
For each unknown slide, you will need to SKETCH a picture of the cells under the scope and LABEL the stage
of development and structures characteristic of that stage. (Hint: determine the order first, then draw.)
Use the internet sites below to help determine the stages, and also, the reference sheet on the back for
structures to label.
http://www.discoverdevelopment.com/PHP/SlidesStarfish.php
http://classes.midlandstech.com/carterp/courses/bio211/Lab/Starfish_Development.html
Data: (Cut or scan this table into your formal report which will have your typed conclusion)
Unknown Slide #:
Stage:
Drawing:
Unknown Slide #:
Stage:
Drawing:
Unknown Slide #:
Stage:
Drawing:
Unknown Slide #:
Stage:
Drawing:
Unknown Slide #:
Stage:
Drawing:
Unknown Slide #:
Stage:
Drawing:
Conclusion: (MAKE SURE THIS SECTION IS IN YOUR OWN WORDS, NOT YOUR LAB PARTNER OR TEXT!)
Describe the process of embryological development. Begin with the unfertilized egg and discuss, in detail,
the changes that occur from slide to slide observed today. Use appropriate terms by referencing your
background handout. How does cell size change from zygote to larval form? From what parts of the
gastrula do the ecto, meso and endo derms form? What causes the cell differentiation? What difficulties
did you have in the lab today? Discuss one idea for further study in embryological development.