1. High molybdenum content in the soil may lead to incoordination in young ruminants due to defective myelination of the nervous system. Molybdenum causes this effect by:
A) A direct destructive effect on myelin
B) Damaging the cells that produce and maintain myelin
C) Interfering with copper absorption to produce a copper deficiency which causes demyelination
D) Activation of a virus which produces demyelination
E) Stimulation of the immune system to produce antibodies against the basic myelin protein
Correct Answer: C
Molybdenum interferes with copper absorption, leading to copper deficiency. Copper is essential for myelination, so its deficiency results in demyelination and neurological symptoms in young ruminants.
2. The purpose of expression time experiments in establishing a mammalian cell culture mutagenicity assay is:
A) To provide information as to how long the cells must be subjected to the mutagen in order to obtain a response
B) To demonstrate at which cell density there is interference with expression of the mutation due to cross-feeding from cell to cell
C) To demonstrate phenotypic lag and indicate the time after treatment that must elapse before the stable mutation is expressed and can be scored
D) To describe the time of focus formation in cell transformation assays
E) None of the above
Correct Answer: C
Expression time experiments account for phenotypic lag—the delay between DNA mutation and phenotypic expression—ensuring accurate scoring of mutations after sufficient expression time.
3. Which of the following statements about lead poisoning is most correct?
A) Any level of lead in the body is considered to cause serious toxicity
B) Tolerance to lead develops with continued exposure
C) Most cases of lead poisoning are due to unusual susceptibility of the individuals concerned
D) Lead retention by the body is cumulative
E) Most cases of lead poisoning result from the acute accidental ingestion of lead-containing drugs
Correct Answer: D
Lead is retained cumulatively in the body, especially in bones and tissues. Chronic exposure builds up toxicity over time. It is not true that tolerance develops or that acute ingestion is the main cause.
4. Dominant lethal mutations:
A) Can be detected as a result of mutagen attack on somatic cells
B) Are not compatible with survival of offspring
C) Cause tumors to develop in surviving offspring
D) All of the above
E) None of the above
Correct Answer: B
Dominant lethal mutations result in embryonic or fetal death and are thus incompatible with offspring survival. They are not somatic mutations and do not cause tumors in surviving offspring.
5. When compared across species, the toxic dose of an agent is generally most closely proportional to:
A) Body weight
B) Surface area
C) Body temperature
D) Body height
E) Age
Correct Answer: B
Surface area is a better predictor of metabolic processes across species than body weight. This is due to differences in metabolic rates scaling with surface area.
6. A rat with a respiratory rate of 100 breaths/min and a tidal volume of 1.25 ml has a minute volume equal to:
A) 0.15 liters/min
B) 0.10 liters/min
C) 0.50 liters/min
D) 0.13 liters/min
E) None of the above
Correct Answer: A
Minute volume = tidal volume × respiratory rate = 1.25 ml × 100 = 125 ml = 0.125 L ≈ 0.13–0.15 L. Closest answer is 0.15 liters/min.
7. In dietary feeding studies, the best method for maintaining a constant treatment or exposure situation is to:
A) Maintain a constant % composition of the test material in the feed
B) Maintain a constant ppm level of the test material in the feed
C) Periodically adjust the composition of the feed to maintain a constant intake of test material based on food consumption and rate of change in body weight
D) Limit the amount of treated feed available to keep food consumption at a constant level
E) Periodically adjust the composition of the feed to maintain a constant intake of test material based on food consumption
Correct Answer: C
Adjusting feed composition based on actual consumption and weight change ensures the dose remains constant regardless of changes in animal metabolism or food intake.
8. A rat sacrificed after 20 months of a 2-year study was found to have gastric hemorrhage, enlarged rough kidneys, fine white streaks in the intestinal muscle and prominent white foci on the thyroid. The best tentative diagnosis is:
A) Secondary hypoparathyroidism due to renal failure
B) Chronic progressive glomerulonephrosis
C) Gastric ulcers with septicemia
D) Nephroblastoma with disseminated metastasis
E) None of the above
Correct Answer: A
The combination of kidney and intestinal lesions, along with white thyroid foci, is consistent with renal failure leading to secondary hypoparathyroidism and calcium-phosphorus imbalance.
9. Which of the following chemicals will be most likely to accumulate in maternal milk (pH 6.8, plasma pH is 7.4)?
A) Weak base that strongly binds to plasma proteins
B) Weak base that does not bind to plasma proteins
C) Weak acid that strongly binds to plasma proteins
D) Weak acid that does not bind to plasma proteins
E) Chemical that is completely ionized at pH 7.4
Correct Answer: B
Weak bases that do not bind to plasma proteins remain free and can diffuse into milk more easily. Milk is slightly more acidic, which promotes ion trapping of weak bases.
14. The hazard of a radioactive isotope in the body is less if:
A) Has a long half-life
B) Is homogeneously distributed throughout the body
C) Emits beta rather than gamma radiation
D) Emits neutrons rather than beta radiation
E) Localizes in a particular organ of the body
Correct Answer: B
Uniform distribution of radiation reduces localized exposure and damage, minimizing risk. Localized concentration increases the hazard regardless of radiation type.
15. Which of the following is most likely to produce permanent population reduction in environmental species?
A) Acute toxic effects in target species
B) Habitat alteration
C) Intra-species competition
D) Use of granular formulations for pesticides
E) Immigration
Correct Answer: B
Habitat alteration disrupts reproduction and survival long-term across generations, unlike acute toxicity which affects only current populations.
19. In doing a linear regression analysis on dose of an agent, you conduct a statistical test on the regression slope and find that it is significant. The interpretation of this result is that:
A) The intercept is large
B) The slope is large
C) The intercept is not zero
D) The slope is not zero
E) Both the intercept and slope are not zero
Correct Answer: D
If the regression slope is statistically significant, it means the slope is not zero—i.e., there is a relationship between dose and response.
