Why are epithelial membranes thin?
a. epithelial tissues cannot support other cells growing on top of the tissue
b. epithelial tissues are not able to grow past several layers because of an interrupted cell cycle which occurs after several complete cell cycles.
c. epithelial tissues can only reach a certain level of thickness because of their pre-programmed cell growth.
d. epithelial tissues are nourished by blood vessels in adjacent tissues, thus diffusion is limited to thin tissues.
e. epithelilal tissues that are much greater than a few cell layers in thickness collapse because of drying conditions caused by the environment.

d. Epithelial tissues are nourished by blood vessels in adjacent tissues, thus diffusion is limited to thin tissues.

Explanation:

Epithelial tissues have tightly packed cells and have no space for blood vessels to be present between adjacent epithelial cells. The cells of the epithelial tissues get nutrients from the blood vessels of neighboring connective tissues.

Since the exchange of nutrients between the cells of the epithelial and connective tissues occurs through diffusion, epithelial tissues are only one to few cells layers thick to allow nutrient supply to all of its cells.

they each offer a fresh glut of resources to the organisms that can arrive and exploit them. as individuals and new species continue to appear, they actively and passively alter the environment. competition for shared resources increases, local abiotic and biotic conditions shift, and the relative abundances of species change accordingly. the process is called ecological succession, and it is one of the earliest and most well-known concepts in ecology.