Answer to Question 1
Stem cells are cells that can develop into different types of body cells; theoretically, they can repair the body. As a stem cell divides, the new cells can remain stem cells or become another kind of cell. It is possible that stem cell research may lead to regenerative or rehabilitative medicine.
Stem cells are special in a number of ways. First, they are unspecialized cells that renew themselves for long periods through cell division. Second, under certain physiologic or experimental conditions, they can be induced to become cells with special functions, such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.
Many scientists feel that stem cell research may hold the possibility of future cures, preventions, and therapies. In November 2006, scientists succeeded in growing heart valves using stem cells from the fluid that cushions babies in the womb. These valves might one day be used for babies born with heart defects. In the past, scientists have either had to use embryonic stem cells or generate embryonic-like stem cellsa difficult process. In 2011, however, scientists at the Scripps Research Institute succeeded in converting adult skin cells directly into beating heart cells. This technology might make possible new treatments for heart disease, Parkinson's disease, and Alzheimer's disease.
Answer to Question 2
B
The structure of stomatal guard cells affects their function.
Sieve-tube elements and companion cells in phloem tissue
Furchgott's discovery that endothelial cells produce a vasodilating substance.
Eukaryotic Cells
Margination, diapedesis, and chemotaxis of white blood cells
a) Preformed mediators released by mast cells and their actions. (b) Newly synthesized mediators ...