Final answer:
Insulin is the chemical substance that aids the transfer of sugar from blood to cells, secreted by the pancreas in response to high blood glucose levels and helps to reduce these levels by promoting glucose uptake and storage as glycogen.
Step-by-step explanation:
Sugar passes from the blood to the cells with the aid of the chemical substance known as insulin. Insulin is secreted by the pancreas in response to elevated blood glucose levels. After a meal, when blood glucose levels become elevated, beta cells of the pancreas release insulin into the blood. This action facilitates the movement of glucose into cells, where it can be used for energy or stored. Excess glucose in the bloodstream is converted to glycogen in the liver and muscles, which helps in reducing blood glucose levels to normal. In contrast, when there is a drop in blood glucose levels, glucagon is released which in turn stimulates the breakdown of glycogen back into glucose to increase blood glucose levels.