Which organ does NOT require insulin to facilitate glucose entry?

The brain is the correct choice because it primarily relies on glucose as its main source of energy and has a unique mechanism for glucose uptake. Unlike other organs that depend on insulin for glucose to enter the cells, the brain utilizes glucose transporters that are insulin-independent. This allows the brain to maintain a steady supply of glucose even when insulin levels are low or when the body's overall glucose levels fluctuate.

In contrast, the liver, pancreas, and stomach have cells that typically require insulin for glucose entry. The liver can store glucose as glycogen or release it into the bloodstream, but this process is regulated by insulin. The pancreas produces insulin in response to elevated blood glucose levels, while the stomach is involved in protein digestion and absorption, not glucose transportation. Thus, insulin plays a crucial role in the glucose metabolism of these organs, making the brain's independent ability to absorb glucose distinctive.