Book 31, Question 53
What is an egg made of, from the yolk to the shell?
An egg is a complete packed lunch for a growing chick.
The yolk is full of fat and protein for food. The clear, thick white around it holds water and cushions the yolk. Thin skins called membranes lie inside the hard shell, which is made mostly of calcium. The shell protects everything and lets air in. Together, the parts give a chick everything it needs to grow.
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Quick answers
What is an egg made of, from the yolk to the shell?
The yolk contains less water and more protein than the white, some fat, and most of the vitamins and minerals of the egg.
Source: Exploratorium
More fun facts
- Opaque ropes of egg white, the chalazae hold the yolk in the center of the egg.
- Lying between the eggshell and egg white, these two transparent protein membranes provide efficient defense against bacterial invasion.
- The shell is porous and the large end contains more pores than the small end of the egg.
- Immediately beneath the shell are two membranes, the outer and inner shell membranes.
- The shell also has a thin outermost coating called the bloom or cuticle that helps keep out bacteria and dust.
- Calcium absorbed from the yolk and shell are used by the embryo to make its bony structure, or skeleton.
Sources: Exploratorium, Penn State