Insulin is a protein that maintains homeostasis in the amount of sugar in the blood. When there are high levels of sugar in the blood, cells in the pancreas generate more insulin and release it into the blood. This causes muscle cells and fat tissue to absorb sugar. When there are low levels of sugar in the blood, the production of insulin is slowed. What is the most likely cause of the phenomenon described?

1. Glucose has a chemical reaction with blood cells to create insulin.
2. The expression of the insulin gene is regulated by blood glucose concentration.
3. Pancreas cells have more copies of the insulin gene than other cells.
4. The body has a surplus of insulin stored in the pancreas and releases it when needed.