The document discusses the biology and composition of eggs. Eggs are laid by many animal species and have long been consumed by humans. They contain a developing embryo and provide complete nutrition for growth. For birds, eggs contain a hard chalky shell, while reptile eggs have a leathery membrane. The interior contains various membranes, the white albumen, a yolk, and in birds, a shell. Eggs are highly nutritious food for humans, with protein, fat, and water contents varying between the yolk, white, and whole egg. Eggs also provide a low-cost source of protein compared to other foods like meat.

2. The egg is a biological structure intended by
nature for reproduction…
Eggs are laid by female animals of many
different species, including birds, reptiles,
amphibians, and fish, and have been eaten
by humans for thousands of years.
an oval or round object laid by a female
bird, reptile, fish, or invertebrate, usually
containing a developing embryo. The eggs
of birds are enclosed in a chalky shell, while
those of reptiles are in a leathery membrane.

3.  It protects and provides a complete
diet for the developing embryo, and serves
as the principal source of food for the first
few days of the chick's life. The egg is also
one of the most nutritious and versatile of
human foods.
When the egg is freshly laid, the shell
is completely filled. The air cell is
formed by contraction of the contents
during cooling and by the loss of
moisture. A high-quality egg has only
a small air cell.

4. Key Vocabulary:
1. chalazae: One of two spiral bands of tissue
that connect the yolk to the lining membrane at
either end of
the shell.
2. shell membrane: There are two different
parts: the inner-shell membrane and the outer-
shell membrane.
The inner membrane is located just between
the outer-shell membrane and the albumen,
while the outer
shell membrane lies just beneath the shell.

5. 4. albumen: The white of an egg
5. air cell: A cavity containing air
6. shell: The hard exterior of an egg
7. germinal disk: A flattened,
disklike region of cells from which
the embryo begins to develop
8. vitelline membrane: The
membrane surrounding the egg yolk

6. Composition
An average-sized egg weighs approximately 57 grams (about 2 ounces). Of
this weight, the shell constitutes 11 percent; the white, 58 percent; and the
yolk, 31 percent. Normally, these proportions do not vary appreciably for
small or large eggs. The percentage composition of the edible portions is:
Percent
Water Protein Fat Ash
Whole egg 74 13 11 1
White 88 11 .. ..
Yolk 48 17 33 1

7. Value of eggs
Food prices continue to climb, particularly
for high-protein foods, and consumers
are constantly searching for ways to
reduce their food bill. One way is to
include more eggs in the diet. Comparing
protein foods on a pound-for-pound
basis, eggs cost about 95 cents a pound
when large eggs are selling for 64 cents a
dozen. It is difficult to purchase any other
high-protein food--meat or fish--for this
low price.