The epidermis of the skin consists of many layers of tightly packed cells. the outermost layer of cells are dead. which best describes why this occurs?

a. chemical compounds containing digestive enzymes are located on the outside of the skin, and they destroy the cells.
b. blood vessels are not located in the epidermis, but in the underlying dermal connective tissue.
c. the outer layer of skin is nervous tissue and nervous tissue will not regenerate.
d. pathogens on the skin secrete toxins that affect the cellular structure, thus destroying the cell.

d. Pathogens on the skin secrete toxins that affect the cellular structure, thus destroying the cell.

Epidermis is the outermost protective layer of skin. It is composed of two layers, the first is the outer stratum corneum, which is typically composed of dead, keratin filled cells and the second one is the living basal layer, which covers the inner dermal layer of skin. The layer stratum corneum is composed of protein keratin is protective against pathogenic agents. It does not allow the absorption of the toxins secreted by the pathogens.    

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.