Introduction
Every animal requires oxygen to live. When animals, including humans, breathe in, oxygen enters the lungs, where it is shuttled into the blood stream and distributed to all the different parts of the body. The oxygen is used in an internal chemical reaction called metabolism to provide the animal with energy. The process of metabolism also produces a waste gas called carbon dioxide. In order to get rid of this waste gas, the blood stream carries the carbon dioxide back to the lungs where it is collected and finally breathed out.
Animals that grow inside their mothers, like humans, get their oxygen from their mothers. The blood stream of the baby animal and the mother are connected through an umbilical cord, which allows the baby to collect oxygen that his or her mother breathes in and use the mother’s lungs to get rid of the carbon dioxide. But how do animals that grow in a shell and do not have umbilical cords, like chickens, take in oxygen and get rid of carbon dioxide?
Bird and reptile eggs have a hard shell. Directly under the shell are two membranes. When the eggs are laid by the mother, they are warmer than the air, and as they cool, the material inside the egg shrinks a little bit. This shrinking pulls the two membranes apart, leaving behind an air cell, also called an air sack, that is filled with oxygen. As the animal develops, it needs the oxygen replenished so it can continue to grow, and it needs the carbon dioxide it is making to be able to escape from the air cell. So, how does this happen? Well, if you examine a chicken egg carefully with a magnifying glass, you will see that there are tiny little holes, called pores, in the shell. A chicken egg shell has more than 7,000 pores! Do you think that the pores could be a way for carbon dioxide to escape and fresh air to get in? In this science project you will determine if substances can move in and out of an egg through these pores. To do this you will soak several raw chicken eggs in water with food color and detergent. Then you will crack the eggs open and look on the inside of their shells. If the pores really do allow materials to cross back and forth between the inside of the egg and the outside environment, then you should see dye on the inside of the shells. Ready to find out the answer? Time to dye some eggs!