MCAT Question of the Day

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.

[php snippet=6]

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: B. Synapomorphies

Plesiomorphies are characteristics that are original in the organism. While apomorhic means “derived characteristic”, the prefix syn- alters the meaning to “shared derived characteristic.” Using the prefix aut- causes the meaning to change to “self-derived characteristic” implying that it isn’t shared by another group. Homoplasy or homoplastic characteristics are shared among groups, but weren’t derived from an ancestral source.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: C. Part of the innate immune system comprised of plasma proteins synthesized primarily by hepatocytes.

The complement system is a clear example of innate immunity, being a form of host defense that is non-specific and does not adapt in response to antigens. However, there is evidence of cross-talk between the complement system and adaptive immunity. Similarly components of the complement system communicate with components of the inflammatory system and hematopoietic system. Nonetheless, complement system components are distinct from leukocytes and the components of the inflammatory system and are primarilysynthesized in the liver.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: B. Phospholipids

The cell membrane is composed of a phospholipid bilayer that has a hydrophilic head (where the polar phosphate is attached) and a hydrophobic tail (made up of hydrocarbon chains). Starch is a polysaccharide that is generally hydrophilic and can be dissolved in water. Triglycerides, steroids and cholesterol are all entirely hydrophobic not being able to be dissolved in water. The molecule mentioned in the question is both hydrophilic and hydrophobic, indicative of the phospholipid, therefore only answer option [B] is correct.

[php snippet=5]

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

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].

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: C. keystone predator

The otter would be considered a SECONDARY consumer, the urchins are the primary consumers, and a hypothetical predator of the otter would be a tertiary consumer. Since the otter is responsible for preventing overgrazing of the small grasses by predating on the out of control urchin population, it is termed a keystone predator that exerts a “top-down” effect on the ecosystem.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: C. 2H2O2 -> 2H2O + O2

The second law of thermodynamics states that nature tends to favor a state of disorder or entropy. In other words, chemical reactions that are exergonic (release energy) and result in more products than reactants are favored. The only answer option that has more products formed in comparison to the reactants is answer option C.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: A. CH4, NH3, H2, H2O

In the primitive atmosphere, no O2 was present as most organisms used chemosynthesis to create organic compounds. The Oparin and Haldane hypothesis states that methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O) were the only gases present. It was after the Miller and Urey experiment that it was proven that these gases and lightning could have given rise to simple organic compounds that then later evolved into more complex forms of life.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: B. It reduces activation energy of a chemical reaction

Enzymes reduce the activation energy of chemical reactions by binding substrate(s) into energetically favorable orientations. They greatly reduce the activation energy, but do not eliminate it completely. Enzymes are completely reusable—they do not participate in the reaction as a substrate. Even when cofactors are needed for the successful action of the enzyme and though they may be tightly bound, they are not covalently bound to the enzyme. Enzymes do not add additional energy to chemical reactions as heat would, for example.

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.

Correct Answer: A. the ventricles, spinal canal, and meninges.

The organs of the central nervous system (CNS), the brain and spinal cord, have hollow regions (ventricles and spinal canal, respectively). The CNS also contains the meninges, which consists of three layers of protective covering. The question states that CSF circulates in these areas. Thus A is the correct answer. The spinal nerves and cranial nerves are not part of the CNS, they are part of the peripheral nervous system (with the exception of cranial nerve II, but that’s a little advanced for the MCAT).

Subscribe below to receive the MCAT Question of the Day delivered straight to your inbox every morning.