Yes, a kangaroo has many cells.
From one parent somatic cell, two daughter cells are created.
Mitosis.
If cells do not divide properly, then many problems can occur, cancer cells for example.
The dying ones have to be replaced. After growth is completed the body enters into replenishment mode. As certain cells die, the body seeks to replace them.
If cells do not divide properly, then many problems can occur, cancer cells for example.
Unlike most cells in an adult body, an embryonic mass of cells is always dividing. Most cells in the adult body is quiscent and will not divide unless signals have been given to them to divide, and many cells such as muscle and nerve cells have even lost the ability to divide.
Stem cells are different from other cells in the body in several notable ways. They can divide and renew themselves many times, whereas other cells are more limited in their divisions. And when those stem cells divide, the new cells can become specialized if necessary. Stem cells have no assigned function in the body, but through the process of specialization, they can take on roles in any of the body's tissues. These type of cells can be derived from human embryos or from certain spots in the adult human body.
Germ cells use a similar, but not identical, process to divide known as meiosis. Many adult cells do not divide at all under normal conditions, such as neurons and red blood cells.
double what the person already had if mitosis is when cells divide into two cells
Mitosis
Considering how we have billions of cells in our body as fully developed fetuses, I'd say billions.