## **Core Concept**
Insulin-dependent entry of glucose into cells is a critical process in glucose metabolism. **Insulin** facilitates the uptake of glucose by cells through the **insulin receptor** and the **glucose transporter type 4 (GLUT4)** pathway. This process is essential for maintaining normal blood glucose levels.

## **Why the Correct Answer is Right**
The correct answer involves tissues that primarily rely on insulin for glucose uptake. **Muscle cells**, especially **skeletal muscle** and **cardiac muscle**, are highly dependent on insulin for glucose entry. When insulin binds to its receptor on the surface of these cells, it triggers a signaling cascade that results in the translocation of GLUT4 to the cell surface, increasing glucose uptake. This process is crucial for glucose storage as glycogen and for energy production.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While the liver does respond to insulin, its glucose uptake is not entirely insulin-dependent. The liver can take up glucose through insulin-independent mechanisms as well.
- **Option B:** Adipose tissue does require insulin for glucose uptake, similar to muscle cells, but the question seems to focus on a more significant and direct insulin-dependent glucose entry.
- **Option D:** The brain's glucose uptake is largely insulin-independent. It uses **GLUT1** for continuous glucose uptake, regardless of insulin levels.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **insulin resistance**, a condition where the body's cells do not respond effectively to insulin, leads to decreased glucose uptake in muscles and adipose tissue. This condition is a hallmark of **type 2 diabetes mellitus** and is associated with obesity, metabolic syndrome, and increased risk of cardiovascular disease.

## **Correct Answer:** . Muscle