A and B. Because if heart cells were located in your brain, your brain would not perform the right function. And B because if cells perform different functions and are in the wrong spot im your body it wouldnt work.
The bell shaped curve indicates polygenic traits. A polygenic trait is controlled by multiple alleles. Hope this makes sense :)
It is important to understand because it's the way all cells reproduce (except sperm and egg cells, they do meiosis), and our cells are the essential parts of our whole being.