# Assignment for developmental biology- chick embryology

Questions

1. Ninety-eight percent of an egg shell is calcite, which is calcium carbonate (CaCO3). Calcium is the major component of bone as well (in the form of calcium phosphate, or apatite). The calcium that goes into the shell comes both from the hen’s diet and from her bones. The average weight of a chicken egg shell is 7.26 grams. A truly remarkable hen can lay an egg a day. In a year, a hen can put into her eggshells over 25 times her own skeletal weight in calcium.

Obviously, this must be replaced. The standard feed given to laying hens is 3 to 4% calcium, and one hen receives about a 100 gm of feed a day. Based on the weight of the shell, is this sufficient to replace the calcium lost in a superhen laying every day? Do the calculations to support your answer.

CaCO3 = 100.9 grams / mole

Atomic weights of molecules from the periodic table.

Ca = 40.08

C = 12.01

O = 16.00

2. Why is the amniote egg considered to be an important evolutionary development?

3. What is the function of the air space in the chick egg?

4. What is the importance of chalazae?

5. Why is initial cleavage of the chick egg meroblastic rather than holoblastic?

6. What is the cavity that underlies the area pellucida? What is its importance relative to the primitive streak?

7. What is the role of the primitive streak and Hensen’s node?

8. Define the term somite.

9. What structure is found between the somites and what is its role?

(550 words)

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