In sodium-dependent glucose transport, i.e., symport or co-transport

Options

A. `Na^+` is transported passively from the lumen into the gut, glucose is transported against concentration gradient
B. `Na^+` and glucose both are transported actively into the gut from lumen
C. `Na^+` and glucose both are transported passively
D. `Na^+` is transported actively and glucose passively

Answer

### Step-by-Step Solution:

1. **Understanding Sodium-Dependent Glucose Transport**: Sodium-dependent glucose transport refers to the mechanism by which glucose is absorbed in the intestines and kidneys using sodium ions. This process is crucial for nutrient absorption.

2. **Identifying the Transport Mechanism**: The transport of glucose in this context is classified as symport or co-transport. This means that both sodium ions (Na⁺) and glucose molecules are transported together across the cell membrane.

3. **Analyzing the Options**:
- **Option A**: Sodium ion is transported passively from the lumen into the gut, and glucose is transported against its concentration gradient.
- **Option B**: Sodium ion and glucose both are transported actively into the gut from the lumen.
- **Option C**: Sodium and glucose both are transported passively.
- **Option D**: Sodium is transported actively, and glucose passively.

4. **Evaluating Option A**: In sodium-dependent glucose transport, sodium ions move down their concentration gradient (from high concentration in the lumen to lower concentration inside the cell), which is a passive process. Meanwhile, glucose is transported against its concentration gradient (from low concentration inside the cell to higher concentration in the lumen), which requires energy. This aligns with the description in Option A.

5. **Conclusion**: Therefore, the correct answer is **Option A**: Sodium ion is transported passively from the lumen into the gut, and glucose is transported against its concentration gradient.