Certain epithelial cells are called pseudostratified columnar epithelium because :

Options

A. they have a layered appearance but all the cells contact the basement membrane
B. they are stratified and all the cells do not contact the basement membrane
C. their muclei are all located the same distance from the cell surface
D. they are a mixture of cell types

Answer

### Step-by-Step Solution:

1. **Understanding the Term "Pseudostratified":**
- The term "pseudostratified" means "false stratified." It indicates that while the epithelium appears to be layered, it is not truly stratified.

2. **Structure of Pseudostratified Columnar Epithelium:**
- Pseudostratified columnar epithelium consists of a single layer of cells. However, these cells vary in height, which gives the illusion of multiple layers.

3. **Nuclear Arrangement:**
- In pseudostratified columnar epithelium, the nuclei of the cells are located at different levels within the tissue. This variation in nuclear position contributes to the appearance of stratification.

4. **Connection to Basement Membrane:**
- All cells in pseudostratified columnar epithelium rest on the basement membrane. This is a key characteristic that confirms it is a single-layered epithelium, as opposed to true stratified epithelium where cells would be stacked on top of one another.

5. **Conclusion:**
- Therefore, pseudostratified columnar epithelium is called so because it has a layered appearance due to the varying cell heights and nuclear positions, but fundamentally, it is a single layer of cells that all contact the basement membrane.

### Final Answer:
Certain epithelial cells are called pseudostratified columnar epithelium because they have a layered appearance but all the cells contact the basement membrane.