Gas exchange also takes place. And that's important because as the fetus is developing the lungs of that fetus do not actually form until after birth takes place. And so the placenta acts as a system where gas exchange takes place. Oxygen goes into the blood and carbon dioxide is expelled as a waste product. And so that leads us directly into function three, waste product removal or function four, waste product removal. What that basically means is not only carbon dioxide is removed by the placenta from the blood of that embryo but also other byproducts wasteful byproducts such as urea.