Receptor-mediated endocytosis :

Options

A. helps to concentrate proteins in vesicles
B. brings specific substances into the cell
C. is not different from phagocytosis
D. all of the above are correct

Explanation

### Step-by-Step Solution:

1. **Understanding Receptor-Mediated Endocytosis**:
- Receptor-mediated endocytosis is a cellular process that allows cells to internalize specific molecules (ligands) by using receptors on their surface. This process is selective, meaning that it targets specific substances rather than all substances in the environment.

2. **Role of Receptors**:
- In this process, specific receptors on the cell membrane bind to particular ligands (the substances to be internalized). Each receptor is designed to recognize and bind to a specific type of ligand, which ensures that only certain molecules are brought into the cell.

3. **Mechanism of Internalization**:
- Once the ligand binds to its receptor, the cell membrane invaginates (folds inward) to form a vesicle that encloses the ligand-receptor complex. This vesicle then detaches from the membrane and moves into the cytoplasm of the cell.

4. **Comparison with Other Processes**:
- While receptor-mediated endocytosis is a form of endocytosis, it is distinct from phagocytosis. Phagocytosis involves the engulfing of large particles or cells (like bacteria) and is not selective, whereas receptor-mediated endocytosis is highly selective and involves the uptake of specific molecules.

5. **Analyzing the Options**:
- The options provided in the question are:
a) Helps to concentrate protein in vesicles
b) Brings specific substance into the cell
c) Is not different from phagocytosis
d) All of the above are correct
- Based on the understanding of receptor-mediated endocytosis, option (b) is the most accurate statement, as it emphasizes the specificity of the process.

6. **Conclusion**:
- Therefore, the correct answer to the question is option (b): "Brings specific substance into the cell."