USA Biology Olympiad (USABO) Practice Exam

Which of the following is an effect of insulin release?

1. Increased blood glucose levels

2. Decreased glycogen stores in liver cells

3. Increased glycogen synthesis

4. Increased fat breakdown

The correct answer is: Decreased glycogen stores in liver cells

The correct choice illustrates the role of insulin in regulating glucose and energy metabolism. Insulin is a hormone produced by the pancreas that primarily lowers blood glucose levels when they are elevated, such as after eating. One of the key effects of insulin is to promote glycogen synthesis in the liver and muscle tissues. When insulin is released, it encourages the conversion of glucose into glycogen, which is then stored in the liver and muscles. This action directly contradicts the idea of decreased glycogen stores; instead, insulin facilitates the increase in glycogen stores. The hormone activates various enzymes that aid in glycogen synthesis while inhibiting glycogenolysis, the breakdown of glycogen. This process is crucial because it helps to regulate energy storage and maintain blood glucose homeostasis after food intake. Moreover, insulin also contributes to lipid metabolism by promoting fat storage and inhibiting fat breakdown, further emphasizing its role as an anabolic hormone that builds up energy stores. This is why increased fat breakdown would not be a correct answer, as insulin functions to promote energy storage rather than its mobilization for immediate use. In summary, the correct choice reflects the fundamental metabolic effects of insulin in promoting glycogen synthesis and storage.