Admission Tests Admission Tests Certifications PCAT Questions & Answers

• Question 141:

  What is the oxidation number of nitrogen in NF3?

  A. -3

  B. 0

  C. +2

  D. +3

  Correct Answer: D

  The sum of the oxidation numbers of a neutral compound is always 0. The oxidation number of fluorine is always −1. Let x represent the oxidation number of N, set up the equation, and solve for x:

  x + (−1) × 3 = 0 –andgt; x = 3

• Question 142:

  What are the relative pKa values of the following compounds?

  I. H2O

  II. NH3

  III. HCl

  IV.

  CH3COOH

  A.

  II > I > IV > III

  B.

  IV > II > III > I

  C.

  III > IV > I > II

  D.

  I > III > IV > II

  Correct Answer: A

• Question 143:

  A population of pea plants has 25% dwarf plants and 75% tall plants. The tall allele, T, is dominant to dwarf (t). What percentage of tall plants is heterozygous?

  A. 0.75

  B. 0.67

  C. 0.5

  D. 0.25

  E. 0.16

  Correct Answer: C

  According to Hardy-Weinberg equilibrium, p + q = 1 and p2 + 2pq + q2 = 1. In this scenario, q2 = 0.25, so q = 0.5. p must also be 0.5.

  2pq is equal to 2 ?.5 ?0.5 or 0.5.

• Question 144:

  As a result of herbicide treatment, nearly an entire population of a grass possesses an herbicide-resistant gene. This is an example of:

  A. Stabilizing selection

  B. Directional selection

  C. Disruptive selection

  D. Sexual selection

  E. Artificial selection

  Correct Answer: B

  Selection that favors one extreme trait over all others is called directional selection. If directional selection continues for many generations, the population will end up with only one allele for that trait.

• Question 145:

  If a population's growth rate is zero, it has likely reached its

  A. Carrying capacity

  B. Full range

  C. Mature age structure

  D. Minimal viable population size E. Intrinsic growth rate

  Correct Answer: A

  The carrying capacity is the maximum number of individuals a habitat can sustain, so when the population size reaches this number, growth will stop.

• Question 146:

  Which of the following is the major way in which nitrogen is assimilated into living things?

  A. Erosion from sediments

  B. Fixation by bacteria

  C. Respiration from the atmosphere

  D. Transpiration

  E. Absorption from soils

  Correct Answer: B

  Plants and animals cannot use inorganic nitrogen. It must be fixed, or reduced to ammonium, in order to enter a living ecosystem.

• Question 147:

  Hemophilia is a sex-linked trait. From which parent(s) did an affected boy inherit the trait?

  A. Both the father and the mother

  B. Impossible to tell

  C. Only the mother

  D. The mother or the father but not both

  E. Only the father

  Correct Answer: C

  Sex-linked, or X-linked, traits can only be transmitted to males through the mother.

• Question 148:

  What will be the genotype of the gametes produced by a Tt individual?

  A. All Tt

  B. 1/2 T and 1/2 t

  C. 1/2 Tt and 1/2 tT

  D. All t

  E. All T

  Correct Answer: B

  Gametes are haploid and have only one allele. Half the gametes from this individual will have the T allele and half will have the t allele.

• Question 149:

  In animals, consuming glucose causes insulin release from the pancreas, which causes the liver and muscles to take in glucose from the blood stream. This is an example of:

  A. Thermoregulation

  B. Negative feedback

  C. Receptor feedback

  D. Circulatory feedback

  E. Positive feedback

  Correct Answer: B

  In negative feedback, when a pathway's output (increased blood glucose) exceeds normal limits, a mechanism is activated that reduces inputs to the pathway (reduction of blood glucose). Conditions are monitored by a control center, and when homeostasis returns, the corrective action is discontinued.

• Question 150:

  Which of the following organisms has a circulatory system in which blood circulates in an internal cavity called a hemocoel?

  A. Birds

  B. Cats

  C. Centipedes

  D. Eels

  E. Earthworms

  Correct Answer: C

  Insects and most mollusks have open circulatory systems. Vertebrates, the phylum Annelida (earthworms), and some mollusks (squid and octopuses) have closed circulatory systems.