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.    

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.