Admission Tests Admission Tests Certifications PCAT Questions & Answers

• Question 221:

  When a population reaches its carrying capacity?

  A. The population size begins to decrease.

  B. The population growth rate approaches zero.

  C. Other populations will be forced out of the habitat.

  D. Density-independent factors no longer play a role.

  E. Density-dependent factors no longer play a role.

  Correct Answer: B

  Within a habitat, there is a maximum number of individuals that can continue to thrive, known as the habitat's carrying capacity. When the population size approaches this number, population growth will stop.

• Question 222:

  In the food chain below, vultures represent grass ?gt; cow ?gt; wolf ?gt; vulture:

  A. Scavengers

  B. Primary carnivores

  C. Detritivores

  D. Secondary consumers

  E. Herbivores

  Correct Answer: A

  Vultures eat carrion, or dead animals, so they are considered scavengers. Detritivores are heterotrophs that eat decomposing organic matter such as leaf litter. They are usually small.

• Question 223:

  A population of 1000 individuals has 110 births and 10 deaths in a year. Its growth rate (r) is equal to:

  A. 0.01 per year

  B. 0.11 per year

  C. 0.1 per year

  D. 0.09 per year

  E. 0.009 per year

  Correct Answer: C

  The growth rate is equal to the difference between births and deaths divided by population size.

• Question 224:

  Which of the following processes is an example of positive feedback?

  A. High blood glucose levels stimulate insulin release, which makes muscle and liver cells take in glucose

  B. Low blood oxygen levels stimulate erythropoietin production which increases red blood cell production by bone marrow

  C. High CO2 blood levels stimulate respiration which decreases blood CO2 levels

  D. Low blood calcium levels stimulate parathyroid hormone release from the parathyroid gland. Parathyroid hormone stimulates calcium release from bones.

  E. Increased nursing stimulates increased milk production in mammary glands

  Correct Answer: E

  In a positive feedback loop, an action intensifies a chain of events that, in turn, intensify the conditions that caused the action beyond normal limits. Nursing stimulates lactation, which promotes nursing. Contractions during childbirth, psychological hysteria, and sexual orgasm are all examples of positive feedback.

• Question 225:

  In which of the following stages of embryo development are the three primary germ layers first present?

  A. Blastula

  B. Zygote

  C. Gastrula

  D. Coelomate

  E. Morula

  Correct Answer: C

  The gastrula is formed from the blastocyst, which contains a bilayered embryonic disc. One layer of this disc's inner cell mass further subdivides into the epiblast and the hypoblast, resulting in the three primary germ layers (endoderm, mesoderm, ectoderm).

• Question 226:

  The structures composed solely of diploid cells:

  

  A. 1, 2, and 3

  B. 3, 4, and 5

  C. 1, 4, and 5

  D. 2, 3, and 4

  E. 1, 2, and 4

  Correct Answer: B

  In flowering plants, the anthers house the male gametophytes (which produce sperm) and the pistils house the female gametophytes (which produce eggs). Eggs and sperm are haploid. All other tissues are solely diploid.

• Question 227:

  The structure in which microspores are produced: A. 3

  

  B. 1

  C. 5

  D. 4

  E. 2

  Correct Answer: E

  Anthers produce microspores (the male gametophytes of flowering plants), which undergo meiosis to produce pollen grains.

• Question 228:

  In ferns, the joining of egg and sperm produces a zygote, which will grow into the:

  A. Gametophyte

  B. Sporophyte

  C. Seedling

  D. Sporangium

  E. Spore

  Correct Answer: B

  In ferns, the mature diploid plant is called a sporophyte. Sporophytes undergo meiosis to produce spores, which develop into gametophytes, which produce gametes.

• Question 229:

  Cyanide is a poison that binds to the active site of the enzyme cytochrome c and prevents its activity. Cyanide is a(n):

  A. Prosthetic group

  B. Cofactor

  C. Reverse regulator

  D. Coenzyme

  E. Inhibitor

  Correct Answer: E

  Enzyme inhibitors attach to an enzyme and block substrates from entering the active site, thereby preventing enzyme activity. As stated in the question, cyanide is a poison that irreversibly binds to an enzyme and blocks its active site, thus fitting the definition of an enzyme inhibitor.

• Question 230:

  The synaptonemal complex is present in which of the following phases of the cell cycle?

  A. Telophase of meiosis I

  B. Metaphase of meiosis II

  C. Metaphase of meiosis I

  D. Metaphase of mitosis

  E. Telophase of meiosis II

  Correct Answer: A

  The synaptonemal complex is the point of contact between homologous chromatids. It is formed when nonsister chromatids exchange genetic material through crossing over. Once meiosis I has completed, crossovers have resolved and the synaptonemal complex no longer exists. Rather, sister chromatids are held together at their centromeres prior to separation in anaphase II.