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.

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Correct Answer: A. 10^-5

Therefore:

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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.

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Correct Answer: B. Allelopathy

Allelopathy is type of INTERFERENCE competition, where the establishment of other individuals who would compete for a mutual resource is prevented, in this case using a toxic chemical. Intraspecific competition(E) occurs when competition occurs within the same species; in this case the plant is competing with all the other species of plants in the area.

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Correct Answer: D. Autoclave

The autoclave is the laboratory proven method for killing bacteria, fungi, and some viruses. It can reach temperatures of 121 °C and 2.7 atm, and the combined pressure and temperature are enough to kill the majority of existing pathogens. However, the autoclave cannot kill some species that are able to form heavy spores or protein coats, which include some viruses and fungi.

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Correct Answer: A. 20 N

There are two forces acting on the string. The buoyant force of the ball upward, the tension in the string downward, and the mass of the ball. Since the ball is stationary, these forces must cancel. Thus, T + w = B, which implies:

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Correct Answer: B. Polarimeter.

A polarimeter is a device used for measuring the angle of rotation of plane-polarized light passed through optically active substances. When passed through these substances, optically active substances will cause the polarized light to rotate to either the left (counter-clockwise). The other instruments listed are unable to distinguish between enantiomeric forms.

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Correct Answer: C. 10 mi*h^-1*s^-1

The formula for acceleration is velocity divided by time:

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Correct Answer: D. halved.

The centripetal force of the car is mv²/r, where m is the car’s mass, v is the velocity, and r is the radius of the circular track. If we double the radius while keeping everything else uniform, the centripetal force will be halved because they are inversely proportional.

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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.

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