In antiport ,

Options

A. Two molecules are transported in same direction across the membrane
B. Only one molecule is transported across the membrane
C. Two molecules are moved in opposite directions across the membrane
D. No transport occurs

Answer

**Step-by-Step Text Solution:**

1. **Understanding Antiport**: Antiport is a type of transport mechanism in which two molecules are moved across a membrane in opposite directions. This is different from other transport mechanisms like symport and uniport.

2. **Identifying the Options**: The question provides four options regarding the definition of antiport:
- Option A: Two molecules are transported in the same direction across the membrane.
- Option B: Only one molecule is transported across the membrane.
- Option C: Two molecules are moved in the opposite direction across the membrane.
- Option D: No transport occurs.

3. **Analyzing the Options**:
- **Option A** describes symport, where two molecules move in the same direction, which is incorrect for antiport.
- **Option B** describes uniport, where only one molecule is transported, which is also incorrect for antiport.
- **Option C** correctly describes antiport, as it involves two molecules moving in opposite directions.
- **Option D** states that no transport occurs, which is incorrect.

4. **Conclusion**: Based on the analysis, the correct answer is **Option C**: Two molecules are moved in the opposite direction across the membrane.