Lab ____: Chicken Egg Investigation
Lab skills: 1, 13, 17, 18, 23, 27
Background: The embryonic development of an organism begins soon after
the fertilization of an egg cell by a sperm. During this period of development the
embryo is protected and nourished by a set of surrounding membranes. As
development proceeds, all of the complex organs and tissues appear in a
definite order.
It is difficult to study human embryological development because the embryo
develops internally in the uterus. For this reason embryos that develop externally have been widely used in
developmental studies. Because of their availability, easily observed features and similarity to mammalian embryo
development, chick embryos are used extensively.
In order for a chick egg to develop, the egg must first be fertilized by a sperm from a male chicken. The egg must be kept
warm by the female chicken or placed in an incubator for 21 days. Eggs purchased in the grocery store usually have not
been fertilized or incubated. In this investigation you will examine the internal structures of an unfertilized chicken egg.
Hypothesis: We think that… (tell me if you think that chicken eggs are or are not well adapted to support an embryo.)
Procedure:
Note: Do not touch the raw eggs with your exposed skin for any reason. They may be carrying pathogens that
could cause us to become seriously ill.
1. Cover your lab work space with two layers of paper towels before getting started.
2. Obtain an unfertilized chicken egg from your teacher and gently crack the egg crosswise on the side of the
petri dish. Separate the two halves of the egg shell as you would to put an egg in a frying pan. Allow the
contents of the egg to drop into the petri dish.
3. Examine the outside of the egg shell with a hand lens. Place the egg shell to the side for later examination.
Describe the texture of the egg shell in your results section.
Figure 1 – Internal Chicken Egg Structures
4. Using Figure 1 as a guide, examine the
internal structures of the chicken egg.
On the surface of the yolk locate a small
white round dot. This dot is the
germinal disk from which an embryo
would form after fertilization. Use a
metric ruler to find the diameter of the
germinal disk in mm. Record this
measurement in your results.
5. Find two dense white cord-like
structures. These structures are called
the chalazae (singular chalaza). Using
forceps gently pull on one of the chalazae. To which egg structure are the chalazae attached?
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6. The white of the egg contains water and a protein called albumen. Notice that the egg white surrounds the
yolk and is fairly thick.
7. Observe the yolk. The yolk of the egg contains fats, minerals and vitamins. These materials, which come
from the liver of the hen, pass to the ovary and become part of the egg. Touch the yolk gently with the
forceps. Note that it is surrounded by a
membrane called the vitelline membrane.
8. Examine the inside of the shell and the
membranes attached to it. Try to locate an
air space between the membranes and
shell. The chick uses the air space only
when it is ready to hatch. At which end of
the egg, the blunt or the pointed end, is
the air space located?
9. Draw the egg you have examined in a box
about the same size as the one to the
right. Label the albumen, yolk, chalazae,
germinal disk, air space, shell membrane,
vitelline membrane and shell.
10. Follow your teacher’s instructions for the proper disposal of the chicken egg and shell. Make sure to wash
your hands thoroughly with soap and warm water.
Analysis:
A. What purpose does the eggshell of a bird’s egg serve?
B. If the shell membranes are removed from the shell and water is added the water will seep out of the shell.
What characteristic of the shell would allow this to occur.
C. What is the likely function of the chalazae?
D. What might the egg white provide for the developing embryo?
E. What might the yolk provide for the developing embryo?
F. In the developing human there is no albumen or yolk serving as a source of nutrients. How does the
human embryo obtain nutrients for growth and development?
G. A chick embryo develops in 21 days but a human embryo develops in about 266 days. Why are longer
periods of development possible in humans and other mammals?
H. Candling is a process by which egg processors look at an egg through a light source to determine whether
the egg has been fertilized. Why is “candling” of chicken eggs important to egg processors?
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