USABO Open Exam 2024-25 questions with verified correct answers, Exams of Nursing

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USABO Open Exam 2024-25 questions

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Insulin injected by diabetics to control blood sugar levels is derived from bacteria whose DNA has been modified by the addition of the human gene for insulin, which is then produced by the prokaryotes. This is an example of: A. acid therapy. B. cloning. C. genetic engineering. D. gene therapy. E. pluripotency. - correct answer-C. genetic engineering. Isolated RNA molecules are generally less stable than DNA at physiological pH because: A. RNA has ribose. B. RNU is always linear. C. RNA has U instead of T. D. RNA is usually single stranded. E. there are many more RNAse enzymes. - correct answer-A. RNA has ribose. Which of the following molecules is able to cross the lipid bilayer? A. antibodies B. ATP C. insulin D. Na+ E. steroid hormones - correct answer-E. steroid hormones

If the rate constant of a first order reaction that converts substrate S into product P is 0.693 min -1 then what is the half life of the reaction? A. 0.010 min B. 0.346 min C. 0.693 min D. 1.000 min E. 1.440 min - correct answer-D. 1.000 min The local swimming pool is contaminated with an organism that is causing "swimmers itch." You think you have identified cyanobacteria in your sample. Which features would you expect this organism to LACK? A. chlorophyll B. cell membrane C. differentiated cell types such as spores, vegetative cells, and heterocysts D. nucleoid region E. nucleolus - correct answer-E. nucleolus Suppose radioactive thymine was added to an actively dividing culture of E.coli bacteria. What would happen if a cell replicated once in the presence of this radioactive base? A. one of the daughter cells, but not the other, would have radioactive DNA B. neither of the two daughter cells would be radioactive C. all four bases of the DNA would be radioactive D. radioactive thymine would pair with nonradioactive guanine E. DNA in both daughter cells would be radioactive - correct answer-E. DNA in both daughter cells would be radioactive If radioactive sulfur ( 35 S) is used in the culture medium of bacteria that harbor bacteriophage viruses, it will later appear in:

A. bacterial RNA. B. bacterial cell walls. C. viral DNA. D. viral RNA. E. viral coats. - correct answer-E. viral coats. Which of the following would probably be LEAST DAMAGED by a lipid-dissolving enzyme (lipase)? A. endoplasmic reticulum B. mitochondria C. ribosomes D. nuclei E. plasma membrane - correct answer-C. ribosomes Five events occur in a cell constituting a cause-and-effect sequence: 1. an enzyme is manufactured at the ribosomes 2. cellulose is deposited in a cell wall 3. a molecule of RNA is transcribed 4. a carbohydrate polymer is synthesized 5. a nucleic acid migrates from nucleus to ribosome The order in which these events occur is: A. 1, 3, 5, 4, 2 B. 2, 1, 4, 5, 3 C. 3, 5, 1, 4, 2 D. 4, 2, 1, 3, 5 E. 5, 3, 4, 1, 2 - correct answer-C. 3, 5, 1, 4, 2 When bacterial cells multiply maximally during the logarithmic phase, the total number of cells (b) after some time interval (t) is equal to the original number of cells (B) multiplied by 2n , where n is the number of generations formed during the time interval: n = t/g and b = (B)(2n ). The generation time (g) for type A cells is 28 minutes (assume no cell death). Estimate the LEAST amount of time required for a population of type A cells to increase by 300 percent.

A. approximately 42 minutes B. approximately 48 minutes C. approximately 52 minutes D. approximately 58 minutes E. more than 62 minutes - correct answer-A. approximately 42 minutes A population of 2800 flowers is in Hardy-Weinberg equilibrium, and 2352 of them are red in color. The red allele [R]is the dominant allele; the allele for white color [r] is recessive. What would be the frequency of heterozygotes in the population? A.. B.. C.. D.. E. .84 - correct answer-C.. The cause of trisomy 21 is: A. error during meiosis. B. chromosomal insertion. C. error during mitosis. D. incomplete duplication of chromosome 21. E. over duplication of chromosome 21. - correct answer-A. error during meiosis. The molecular weight of fumarate is 160.0. How many grams of fumarate are there in 200 mL of a 0.1 M fumarate solution? A. 0.32 grams B. 3.20 grams

C. 8.00 grams D. 80.00 grams E. 3.20 kg - correct answer-B. 3.20 grams

16. Replacement of a lysine with a glycine in a protein could result in all of the following EXCEPT a : A. change in the quaternary structure of the protein. B. change in the secondary structure of the protein. C. loss of catalytic activity of the protein. D. loss of a negatively charged side chain. E. loss of the protein's ability to interact with other proteins. - correct answer-D. loss of a negatively charged side chain. The bacterial genome was sequenced and a mutation found in a gene adjacent to β-galactoside. How would you best explain these research findings? The: A. sequencing data is incorrect. B. mutation lies in a regulatory gene. C. mutation renders the enzyme responsible for lactose transport sensitive to high temperatures. D. promoter protein in this pathway must be mutated such that it is denatured by the higher temperature. E. mutation must lie in the operator gene. - correct answer-C. mutation renders the enzyme responsible for lactose transport sensitive to high temperatures. Researchers found that the arginine code AGG is poorly represented in genes of E.coli. Interestingly, they also found that this triplet, when present, binds to the ribosome 7-9 base pairs upstream from the starting ATG triplet (methionine). What does this information suggest in regard to the AGG codon? A. it is a codon rarely found in this bacterium B. it is conserved in most prokaroytic organisms C. it may have a regulatory function in the cell

D. both B and C E. A, B and C - correct answer-C. it may have a regulatory function in the cell The diversity of animal and plant species found on the Galapagos Islands differs from that of the mainland because of: A. climate change. B. convergent evolution. C. divergent evolution. D. parallel evolution. E. random distribution. - correct answer-C. divergent evolution. In many species of flowering plants, the characteristics of the flower; its scent, color, time of flowering, time of day it opens, kind and amount of food it offers, are matched to the pollinating organism's size, form, physiology and reproductive cycle. The term that describes this relationship is: A. convergent evolution. B. coevolution. C. divergent evolution. D. parallel evolution. E. pseudoevolution. - correct answer-B. coevolution. Mountain goats may have a thicker coat of hair than goats at lower altitudes in the same general geographical area. This adaptation to the cooler climate of the mountains most likely arose as a result of: A. allopathic selection. B. bottleneck effect. C. directional selection. D. genetic drift.

E. stabilizing selection. - correct answer-C. directional selection. A given polyclonal antibody molecule can bind to: A. only one molecule of antigen per antibody molecule. B. more than one molecule of the same antigen per antibody molecule. C. two different antigens at once. D. more than one epitope on the same antigen molecule. E. two different epitopes at once. - correct answer-B. more than one molecule of the same antigen per antibody molecule. If a mouse is exposed to cycles of 12 hours of light followed by 12 hours of dark, the mouse is mostly active in the dark and has a rest-activity cycle of 24 hours. If the mouse is then kept in a constantly dark environment, the period of the rest-activity cycle is slightly less than 24 hours. Why does the mouse's cycle shorten in the dark environment? A. the mouse's clock genes get harmful mutations B. the mouse's circadian clock requires environmental cues to reset it C. the mouse's circannual rhythm is inhibited D. the mouse's pineal gland secretes too much melatonin E. the mouse's suprachiasmatic nuclei are over-stimulated by the darkness - correct answer-B. the mouse's circadian clock requires environmental cues to reset it Why is pepsinogen secreted as a zymogen into the stomach? To: A. change the pH of the stomach fluids to aid digestion. B. digest complex carbohydrates. C. digest tough cellulose material. D. inactivate pepsinogen. E. prevent digestion of the gastric glands. - correct answer-E. prevent digestion of the gastric glands.

The anatomy of an animal from a cold climate differs from that of an animal from the tropics in that: A. the animal from the cold climate has smaller ears. B. the animal from the cold climate has larger ears. C. the animal from the tropics has more fat. D. the animal from the tropics has a more spherical body shape. E. there is no difference except perhaps for coloration. - correct answer-A. the animal from the cold climate has smaller ears. A person suffering from nerve gas exposure is given atropine to counteract the effects. Why? A. atropine binds to the nerve gas and inactivates it B. atropine inactivates acetylcholine esterase and allows more acetylcholine to cross the synaptic cleft C. atropine blocks the acetylcholine receptor which blocks the excess acetylcholine lingering in the synaptic cleft D. atropine blocks the sites where nerve gas acts E. atropine stimulates the production of an enzyme that breaks down the nerve gas - correct answer-C. atropine blocks the acetylcholine receptor which blocks the excess acetylcholine lingering in the synaptic cleft Which of the following does NOT describe synovial joints? A. bones held together by cartilage B. joint cavity C. joint surfaces of bones covered with articulating cartilage D. most freely movable of joints E. two-layered joint capsule - correct answer-A. bones held together by cartilage Which of the following processes aid in skeletal muscle relaxation after contraction?

A. acetylcholinesterease degrades acetylcholine B. calcium is released from intracellular storage sites C. motor neurons send electrical signals to the muscle D. sodium is released from intracellular storage sites E. troponin binds calcium - correct answer-A. acetylcholinesterease degrades acetylcholine In India, "night blindness" is a condition mostly found in children, but it can also be found in adults. This condition is an early sign of: A. cataracts. B. glaucoma. C. myopia. D. retinal degeneration. E. vitamin A deficiency. - correct answer-E. vitamin A deficiency. A dog was kept in a room at a temperature of 40°C for two weeks. At the end of that time, it was determined that the dog was sterile. An investigator conjectured that the high temperature had caused the animal's sterility. In order to conjecture this hypothesis, an investigator should be able to show that: A. a cat kept in the same room did not become sterile. B. the dog's pituitary gland had not degenerated. C. the dog was homozygous for temperature sensitivity. D. the dog was not sterile before the experimental period began. E. the high temperature did not alter the dog's blood pressure. - correct answer-D. the dog was not sterile before the experimental period began. An antidiuretic hormone: A. decreases absorption of urea.

B. decreases plasma glucose after meals. C. decreases sodium reabsorption from the ascending limb of the Loop of Henle. D. increases free-water transfer from the distal convoluted tubule and collecting duct to the capillary blood. E. increases osmolarity. - correct answer-D. increases free-water transfer from the distal convoluted tubule and collecting duct to the capillary blood. Which one or combination of the following explains why patients with sickle cell anemia have difficulty breathing at high altitudes? 1. elongation of the red blood cells reduces surface to volume ratios 2. self- associated hemoglobin proteins have altered cooperative binding affinities 3. soluble oxygen is unable to diffuse through the membrane of red blood cells in sickle cell patients A. 1 only B. 1 and 2 only C. 1 and 3 only D. 2 and 3 only E. all of the above - correct answer-B. 1 and 2 only Which of the following is NOT required by nitrogen-fixing organisms for growth? A. carbon dioxide B. nitrate C. nitrogen D. oxygen E. all are required - correct answer-B. nitrate The photobiont of a lichen is most likely to be: A. green algae or cyanobacteria. B. green or red algae.

C. moss or cyanobacteria. D. red algae or moss. E. sponge. - correct answer-A. green algae or cyanobacteria. Xerophytic adaptations are exemplified by which combination of the following features? 1. stomata close at night and open during the day 2. rolled leaves 3. thick waxy cuticles 4. reduction in leaf area 5. hairy leaves A. 1, 2 & 3 B. 1, 2, 3 & 4 C. 2, 3 & 4 D. 2, 3, 4 & 5 E. all of the above - correct answer-D. 2, 3, 4 & 5 The denitrifying activity of denitrifying bacteria will be REDUCED by which of the following? A. decrease in oxygen concentration B. decrease in nitrogen concentration C. increase in nitrate concentration D. increase in oxygen concentration E. increase in soil moisture content - correct answer-D. increase in oxygen concentration Of the following statements, which combination correctly represents the characteristics of primary production?

1. it is carried out only by green plants
2. it is carried out only by photoautotrophs
3. it determines the total energy flow through an ecosystem
4. it determines the amount of life that an ecosystem can support
5. gross productivity minus respiration is equal to net productivity

A. 1, 2, 3 & 4

B. 2, 3 & 4

C. 2, 3 & 5

D. 2, 3, 4 & 5

E. all of the statements - correct answer-D. 2, 3, 4 & 5 Cattle trample and kill small plants surrounding a water hole as they stand near it to drink water. This is an example of: A. amensalism. B. Batesian mimicry. C. commensalism. D. Mullerian mimicry. E. mutualism. - correct answer-A. amensalism. If you were to see a child pulling a toy, followed by three young domestic geese, which of the following would be the most likely explanation for the goslings' behavior: A. associative learning. B. displacement. C. imprinting. D. instinct. E. training. - correct answer-C. imprinting. The movement of water from the soil to the top of a tall tree is primarily the result of: A. active transport of water from xylem vessels into leaf cells. B. active transport of water into xylem vessels. C. higher water potential in leaf cells as compared to root cells.

D. root pressure. E. transpiration. - correct answer-E. transpiration. If a scientist adds a chemical that specifically inhibits diffusion of protons out of the thylakoid through the ATP synthase complex, the result would be: A. an increase of NADP in the interior of the thylakoids. B. an increase in the pH in the interior of the thylakoids. C. increased production of ATPs. D. no net change in ATP production. E. the proton motive force increases. - correct answer-E. the proton motive force increases. When Darwin covered the tip of an oat coleoptile with foil and then illuminated it from one side, the coleoptile: A. bent away from the light. B. failed to grow toward the light. C. grew toward the light. D. had reduced growth in length. E. wilted and died. - correct answer-B. failed to grow toward the light. According to the pressure-flow hypothesis of phloem transport: A. combination of a high turgor pressure in the "source" and transpiration water loss from the "sink" moves solutes through phloem conduits B. formation of starch from sugar in the "sink" increases osmotic pressure C. pressure in the phloem of a root is normally greater than the pressure in the phloem of a leaf D. solute moves from a higher concentration in the "source" to a lower concentration in the "sink"

E. water is actively transported into the "source" region of the phloem to create the needed turgor pressure - correct answer-D. solute moves from a higher concentration in the "source" to a lower concentration in the "sink" During the reproductive process, all of the following transitions occur EXCEPT that the: A. microspores become pollen grains. B. ovulary becomes a fruit. C. ovules become seeds. D. flower petals fall off. E. tube nucleus becomes a sperm nucleus. - correct answer-E. tube nucleus becomes a sperm nucleus. In order to flower, what does a short-day plant need? A. burst of red light in the middle of the night B. burst of far-red light in the middle of the night C. day that is longer than a certain critical length D. higher ratio of Pr : P fr during the day E. night that is longer than a certain critical length - correct answer-E. night that is longer than a certain critical length Which of the following is the function of arbuscules in endomycorrhizae? To: A. aid the digestion of dead organic matter in the soil. B. serve as a nutrient/water bridge between fungus and plant root. C. serve as a reproductive structure. D. store nutrients that have been digested. E. all of the above. - correct answer-B. serve as a nutrient/water bridge between fungus and plant root. The subkingdom Eumetazoa branches into which of the following taxonomic clades?

A. deuterostomia and protostomia B. lophotrochozoa and ecdysozoa C. parazoa and bilateria D. radiata and bilateria E. radiata and parazoa - correct answer-D. radiata and bilateria