Which of the following structures are NOT considered modifications of the cell membrane ?

Options

A. desmosomes
B. terminal bars
C. basement membrane
D. microvilli.

Explanation

To determine which of the given structures are NOT considered modifications of the cell membrane, we need to analyze each option provided:

1. **Desmosomes**: These are specialized structures that function to adhere cells together, particularly in tissues that experience significant mechanical stress. They are indeed considered modifications of the cell membrane as they involve the interaction of membrane proteins.

2. **Terminal Bars**: These are junctional complexes found in epithelial cells, which include tight junctions and adherens junctions. They are also considered modifications of the cell membrane because they involve the organization and interaction of membrane proteins.

3. **Basement Membrane**: This is a thin, fibrous layer that lies beneath epithelial tissues and is composed of proteins and polysaccharides. It is not a modification of the cell membrane itself; rather, it is a non-cellular structure that supports and anchors epithelial cells. Therefore, this is the correct answer to the question.

4. **Microvilli**: These are tiny, finger-like projections that extend from the surface of epithelial cells, increasing the surface area for absorption. Microvilli are considered modifications of the cell membrane as they are extensions of the plasma membrane.

Based on this analysis, the structure that is NOT considered a modification of the cell membrane is:

**Answer: Basement Membrane**