Categorization of epithelial tissue is based on this

The correct option is structural modification.

Epithelial tissues are classified primarily based on two structural characteristics: the number of cell layers and the shape of the cells themselves. These physical or structural modifications determine the specific type of epithelium, which in turn relates to its function. Let us break down this classification step-by-step:
1. Number of Cell Layers:
- Simple Epithelium: Composed of a single layer of cells, typically found where absorption, secretion, and filtration occur (e.g., lungs, kidneys).
- Stratified Epithelium: Consists of two or more layers of cells stacked on top of each other, providing protection in areas subject to wear and tear (e.g., skin, esophagus).
2. Shape of the Cells:
- Squamous: Flat, scale-like cells.
- Cuboidal: Box-like, cube-shaped cells (width is roughly equal to height).
- Columnar: Tall, column-like cells (height is greater than width).
By combining these structural features (e.g., simple squamous, stratified cuboidal), epithelial tissues are categorized. Therefore, the categorization is based on structural modification.