Science Assessment

A hen lays a fertilized egg that will develop into a chick. The egg shell has tiny holes in it that allow gases to enter and leave the egg. (For these questions, assume that oxygen, carbon dioxide, and water vapor are the only gases that enter and leave the egg). The yolk inside the egg is a source of energy and building materials for the growing chick. Therefore, as the chick grows bigger, the yolk gets smaller.

Why does the yolk get smaller as the chick grows?

1. The yolk gets smaller because some of the molecules from the yolk are added unchanged to the chick’s body.
2. The yolk gets smaller because some of the molecules from the yolk are broken down and assembled into new molecules that become part of the chick's body.
3. The yolk gets smaller because all of the molecules from the yolk are broken down and leave the chick’s body as waste. Nothing from the yolk becomes part of the chick’s body.
4. The yolk gets smaller because all of the molecules from the yolk are used by the chick as a source of energy. Nothing from the yolk becomes part of the chick’s body.