Did you know that eggs are the largest cells in the human body?

Unlike sperm cells, which measure only about 0.05 mm, the human egg is approximately 0.1 mm in diameter, about the exact size of the period at the end of this sentence. If you placed 10 eggs side by side, they would measure only about 1 millimeter, roughly the thickness of a credit card.

Something so small, yet capable of beginning an entire life.

Inside this tiny sphere, extraordinary things happen: it contains 50% of the DNA that will form a new human being. It also contains the most active mitochondria in the body.

What are mitochondria? Mitochondria are structures inside each cell that function as its energy source, converting nutrients into usable energy so the cell can operate properly. In the egg, they provide the energy needed at the exact moment of fertilization. At the instant a sperm fertilizes the egg, the egg releases a chemical reaction that automatically blocks the entry of any other sperm a mechanism known as the polyspermy block.

Unlike sperm, which are produced continuously, women are born with all the eggs they will ever have. Once an egg is released, it has only about 12 to 24 hours to be fertilized.