PCAT Online Practice Questions and Answers

Correct Answer: A

The question stem asks you to determine the frequency of individuals expressing the dominant trait in a genetically stable population. However, before you do that, you need to determine the allelic frequencies in the population. This question involves a practical application of the Hardy-Weinberg equation. The Hardy-Weinberg equilibrium states that within a genetically stable population, the gene frequencies of dominant and recessive alleles will not change over time. Two mathematical expressions are associated with the Hardy-Weinberg equilibrium. The first relationship, p + q = 1, describes the relative allelic frequencies in a population. p is defined as the frequency of the dominant allele and q is defined as the frequency of the recessive allele, and the sum of both those frequencies adds up to 1, or 100%. The second relationship, p2

+ 2pq+ q2 = 1, describes the relative genotypic frequencies in the population. p2 represents homozygous, or dominant pp genotypes; q2 represents homozygous, or frequency of the dominant allele, p, by the mathematical relationship p + q = 1. Therefore, the frequency of p is 0.4 because 0.6 + 0.4 = 1. Next, you need to determine the frequency of individuals expressing the dominant trait by recessive qq genotypes; and 2pq represents the frequency of heterozygotes, or hybrids.applying the second relationship, p2 + 2pq+ q2 = 1. The individuals expressing the dominant trait are those that have the pp and pq genotypes, so to find the total frequency of individuals expressing the dominant trait, you add p2 and 2pq. Thus, p2 = 0.4 ? 0.4, or 0.16 and 2pq = 2 ?0.6 ?0.4, or 0.48. If you add the two together, you get 0.16 + 0.48, or 0.64. Thus,

0.64 is the correct frequency of individuals expressing the dominant trait.

Correct Answer: C

Glycogen is considered the principal storage form of glucose and is found mainly in the liver and muscle, with kidney and intestines adding minor storage sites. Glycogen is formed by the liver from glucose in the bloodstream and is stored in the liver. Glycogen is also produced by and stored in muscle cells; during short periods of strenuous activity, energy is released in the muscles by direct conversion of glycogen to lactic acid. During normal activity, energy is released by metabolic oxidation of glucose to lactic acid. Glycogenesis (formation of glycogen from glucose) and glycogenolysis (break down of glycogen into glucose) are two principal mechanisms by which blood glucose level has been maintained.

Correct Answer: C

Resonance describes the possible positions of electrons within a molecule when more than one possibility exists. Molecules that have multiple resonance structures display greater stability than those with fewer resonance structures.

Correct Answer: D

The free energy change of a reaction, ∆G, is equal to the difference between ∆H, the change in enthalpy, and the product of the temperature, T, with the change in entropy, ∆S, of the system: ∆G = ∆H − T∆S. An endothermic reaction requires a ∆H > 0. Solve for ∆H in each case. (A): 0, (B): −894, (C): −298.

Correct Answer: B

The product of the initial concentration and the initial volume is equal to the product of the final concentration and the final volume of the solution. This can be remembered as: c1 ?v1 = c2 ?v2 Substitute the known quantities and solve for the unknown: c1 : c1 ?50mL = 10M ?250mL ?gt; c1 = 50M

Correct Answer: A

PCC is a mild oxidizing reagent used to oxidize primary alcohols to aldehydes. Ethanol, a primary alcohol, treated with PCC results in a 2 carbon aldehyde (because of the 2 carbons initially present in ethanol) called ethanal, or acetaldehyde.

Correct Answer: D

Oxidation numbers provide a way to keep track of the movement of electrons in a reaction. Several rules govern how oxidation numbers are calculated, but in this situation, it's only important to recognize the oxidation numbers of the common components attached to nickel [Ni] on the reactant side and to remember that the sum of the internal oxidation numbers of a molecule equals that molecule's net charge. In this case, nickel oxide [NiO(OH)] is neutral, so the sum of its internal oxidation numbers must be 0. Hydroxide [OH-] always has an oxidation number of -1, and oxygen [O] almost always has an oxidation number of -2. To make these charges cancel out to equal 0, the oxidation number of nickel [Ni] must be +3: 3 - 1 - 2 = 0.

Correct Answer: D

The bottleneck effect occurs when populations undergo a dramatic decrease in size. It could be due to natural or artificial causes.

Correct Answer: D

Graham's Law of Diffusion states that the rate of diffusion is inversely proportional to the molecular weight of the molecule. Let the initial molar mass be 5, and the increased molar mass be 10, substitute these values into Graham's equation and compare the results:

The rate has decreased with the increase in molar mass.

Correct Answer: B

y = x + 5, and you were told that x = -3. Fill in the missing information for x, then solve: y = (-3) + 5y = 2