MCAT Question of the Day fully solved rated A+

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. A blood cell is placed into a salt-water mixture (70% salt). What is likely to result if the red blood cell's membrane is permeable to water? A. The cell will burst B. The cell will shrivel C. The cell will degrade D. The cell will shrivel, then expand - correct answer Correct Answer: B. The cell will shrivel. For cells with a selectively permeable membrane, water will move from higher water concentrations to lower water concentrations. In this problem, the salt is too large to cross the membrane, so the salt concentration will remain the same. Since red blood cells have more water than the salt-water mixture, the water in the cell would leave to try to make the two environments isotonic. If water leaves the cell, the cell will eventually shrink. Which reagent would you choose to convert hexan-1-ol to hexanal? A. PCC/CH2Cl2 B. DIBAL/diethyl ether C. KMnO4/aqueous H2SO4/acetone. D. K2Cr2O7/aqueous H2SO4/acetone. - correct answer Correct Answer: A. PCC/CH2Cl2. Pyridinium chlorochromate (PCC) is a mild oxidant, which converts primary and secondary alcohols to aldehydes and ketones respectively. KMnO4 and K2Cr2O7 are harsher oxidants, and would further oxidize primary alcohols to the corresponding carboxylic acids. Di-isobutylaluminum hydride (DIBAL) is a reducing agents. A construction worker uses a crane to vertically lift an object weighing 2000 N to the top of a platform at a constant rate. If it takes 30 seconds to lift the object 150 meters, what is the rate of energy consumed by the motor in the crane? A. 5.0 kW B. 8.0 kW