1. A
Enzymes are protein catalysts that increase the rate of a
reaction by reducing the activation energy necessary for it to
proceed. Activation energy is defined as the minimum amount of
energy required for a reaction to occur.
Before we examine the other answer choices, let's discuss
reaction thermodynamics. All chemical reactions are accompanied
by energy changes. These energy changes are described by a
function – Gibbs free energy (G) – that denotes the energy of a
system available to do work. The change in free energy (deltaG)
for a given reaction can be determined from the equation ΔH -
TΔS, where ΔH is the change in enthalpy (heat absorbed or evolved
by the system), T is the absolute temperature, and ΔS is the
change in entropy (degree of randomness).
During the course of an enzyme-catalyzed reaction, ΔG does not
change. Thus, according to the above equation, ΔH and ΔS do not
change either, so choices B and C are incorrect. Choice D is
incorrect because an enzyme does not change the energy state of
either the reactants or the products of a reaction—it works by
producing more favorable reaction kinetics, which results in
lowering the activation energy.
2. C
This is a "probability" genetics question that can be answered by
practical application of Mendel's Laws. Mendel's Law of
Segregation states that alleles segregate during meiosis,
resulting in gametes that carry only one allele for any given
inherited trait (i.e., haploid gametes). Mendel's Law of
Independent Assortment states that unlinked genes assort
independently during meiosis. By applying Mendel's Laws, we can
conclude that each parent in the problem can produce two possible
gametes. The father can produce the gametes GH and gH, and the
mother can produce the gametes gH and gh. The probability of the
father's genotype (GgHH) appearing in the progeny can be
determined by calculating the number of different gamete
combinations that will produce this genotype. Thus, a GgHH zygote
can only be produced by the fusion of a GH gamete and a gH
gamete.
The probability that one parent will donate a particular
gamete is independent of the probability that the other parent
will donate a particular gamete. Thus, the probability of the
father donating a GH gamete is =, and the probability of the
mother donating a gH gamete is =. The probability of producing a
genotype that requires the occurrence of both these independent
events is equal to the product of the individual probabilities
that these events will occur. Thus = x = = <, so the
probability that this couple will have a child with the genotype
GgHH is <, or choice C.
3. B
The thylakoid sacs contain chlorophyll, the photopigment that
absorbs light in photosynthesis. They are arranged in
columns.
4. B
Only ionic compounds (electrolytes) dissolved in polar solvents
will conduct electricity. Sugar is a covalent solid, and
therefore is not an electrolyte even when dissolved in water.
Answers (C) and (D) are incorrect because salt will not dissolve
appreciably in an organic solvent, and oil and water are
immiscible. NaCl is an ionic compound, so (B) is correct.
5. A
Here's a question where you might look for answer choices that
are functionally similar to the words in the stem pair. In the
stem pair, to FILTER is to remove the IMPURITY from something. To
filter water, for instance, means to remove dirt and sediment
from it. Analogously, to expurgate is to remove the
obscenity from something, usually a piece of writing. (B)
doesn't fit the bridge because to whitewash is "to cover
up." In (C), perjury is lying during testimony, when
you've sworn to tell the truth.
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6. C
In one mole of NaOH, there are one mole of sodium, one mole of
oxygen and one mole of hydrogen. Because the molar masses of
sodium, oxygen, and hydrogen are 23 g/mol, 16 g/mol, and 1 g/mol,
respectively, there are 16 g of oxygen, 23 g of sodium, and 1 g
of hydrogen in one mole of sodium hydroxide. Therefore, the
percent composition by mass of oxygen in sodium hydroxide is
equal to the mass of one mole of oxygen, 16 g, divided by the
mass of one mole of sodium hydroxide (23+16+1) multiplied by 100.
This is equal to 16/40 X 100—40%.
7. C
Erythrocytes (red blood cells) are formed in the bone marrow,
where they lose their nuclei, mitochondria, and membranous
organelles.
Choices (A), (B), and (D) are all incorrect because they refer to
cells that contain nuclei.
8. D
The first thing that you must do is find out how much each sale
item costs (90/6 = 15 cents). To find how much you save per
package, subtract from the normal price (19 cents) the sale price
(15 cents). The total savings is 4 cents per package. 4 cents
times 24 packages = 96 cents.
9. B
The easiest way to find a in this question is to add the
equations together. 2a + 4a = 6a, -b + b =
0, and 1 + 17 = 18, so you're left with 6a = 18. Dividing
both sides by 6 gives you a = 3.
10. B
Note that the two words in the stem pair are tough opposites. If
you PARAPHRASE something, it, by definition, will not be
VERBATIM, or word for word. Likewise, if you estimate
something, by definition, it will not be precise.
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