MCAT Question of the Day correctly answered

MCAT Question of the DayWhich layer of the epidermis is characterized by a low rate of mitosis and a high concentration of keratin? A. Stratum basale B. Stratum spinosum C. Stratum corneum D. Stratum lucidum - correct answer Correct Answer: C. Stratum corneum If a layer of epidermis has a low rate of mitosis, this indicates that the cells in this layer are not dividing very frequently. Likewise the presence of keratin, signals that the layer of epidermis must have a waterproofing function. The stratum basale is the most mitotic layer and is the bottom layer of the epidermis. As the cells are produced in the stratum basale, older cells are pushed up to the stratum spinosum, which is also high in mitotic activity. Keratin dominates in the stratum corneum, which is the most superficial layer of the epidermis, characterized by dead skin cells that are no longer undergoing mitosis. Therefore, the correct answer is [C]. Pulmonary alveolus (plural form:alveoli) is an integral component of the mammalian respiratory system, which of the following characteristics describes this component? a) Actively transports O2 into the bloodstream b) Allows for gas diffusion to occur and the exchange of CO2 for O2 in the bloodstream c) Hollow cavities at the end of the respiratory tree d) B and C - correct answer The correct answer is D. Alveoli are found in the parenchyma of the lungs at the terminal end of the respiratory tree. Alveoli in the lungs of mammals are the key structure in facilitating the exchange of CO2 and O2 across the alveolar membrane by pumping CO2 rich blood from the body into the oxygen rich alveoli and allowing the exchange to occur through diffusion, not active transport.