The following 3 pages may be duplicated and given to students. This lesson should take 25 35 minutes. Answers: 1. No embryo, 2. I, 3. F, 4. H, 5. G, 6. C, 7. B, 8. A, 9. D, 10. E, 11. Shell, 12. Outer Shell membrane, 13. Vitelline membrane, 14. Inner shell membrane, 15. Chalaza, 16. Albumin, 17. Blastodisc, 18. Yolk, 19. air space.
OBSERVING A FERTILIZED UNINCUBATED CHICKEN EGG
I. Materials-Egg, fingerbowl, scissors, cotton, forceps, dissecting needle.
II. Procedure and Observation
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1. Prepare a bed of cotton in a fingerbowl. Place the egg down so it is held in position by the cotton.
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2. Observe the shell which is composed of calcium carbonate and provides a protective covering. Although it is hard, it is also porous. Observe the larger end of the egg for the small pores which are the largest here. The pores allow for an exchange of gases and moisture.
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3. Open the shell by inserting the scissors and cutting out a small circle. If you cannot easily get your scissors inside try gently breaking a small hole with the dissecting needle. If you have an accident transfer the inside of the egg to a fingerbowl filled with water. (Note: If the yolk has been damaged you will need another egg.
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4. Look for an
air space
at the larger end. The air space acts as a cushion and will be the place where the chick draws its first breath. The space results when the egg is laid. The hen’s body temperature is higher than the outside environment causing the inside of the egg to shrink due to the cooling which occurs.
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5. Near the air space you should be able to observe a membrane surrounding the white or
album
in of the egg. This is the
inner shell membrane.
The
outer shell membranes
may be observed on the pieces of shell which were removed in step 3. It is attached to the inside of the shell. The membranes function to protect the inside from evaporation and bacterial invasion.
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6. Observe the albumin. The albumin provides protein for growth. Notice the opaque cords located in the albumin which connect to the yolk. These are composed of a special protein and function to hold the yolk in place. They are the
chalazae
(singular=chalaza).
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7. Observe the large yellow
yolk
which contains protein, fat, carbohydrates, minerals and vitamins. When combined with oxygen which has been taken in the yolk provides food for the embryo. An invisible membrane, the
vitelline membrane
, surrounds the yolk and embryo.
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8. On the upper surface of the yolk look for a red “blood” spot. This will identify the position of the embryo which can be seen as a small white spot. The area where the embryo develops is called the
blastodisc
. Examine this area with a dissecting microscope if possible.
III. Summary
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1. How does a fertilized egg differ from an unfertilized egg?_________________
Match the following terms with their descriptions.
_____2. shell
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A. greatest amount of protein
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_____3. blastodic
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B. provides embryo with nourishment
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_____4. chalaza
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C. surrounds embryo and yolk
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_____5. air space
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D. surrounds the albumin
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_____6. vitelline
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E. attached to the shell membrane
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_____7. yolk
|
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F. area in which the embryo develops
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_____8. albumin
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G. located at the large end of the egg
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_____9. Inner shell
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H. thicken portion of albumin membrane
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10. Outer shell I. hard protective covering membrane
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____
Using the above terms label the diagram found on the following page by placing the correct term on the line proper number.
11 _______________
12 _______________
13 _______________
14 _______________
15 _______________
16 _______________
17 _______________
18 _______________
19 _______________