Final exam study guide: Practice exam 3

Here are some practice questions for the final exam. There are 30 questions, just like the real final, so I suggest you give yourself two hours to answer them. When you're done, you can see the answers.

  1. You want to know whether playing football increases the probabililty of brain damage. You obtain autopsy reports on 48 former football players, record the number of years that each person played, and determine whether or not they had chronic traumatic encephelopathy. Which test should you use?
  2. You want to know whether salt marsh restoration affects the proportion of black ducks in an area. You go to 10 degraded salt marshes and count the number of black ducks and the number of ducks in other species at each marsh. The marshes are restored, and three years later, you count the number of black ducks and number of other ducks at each marsh again. Which test should you use?
  3. You want to test the effects of anabolic steroids on the muscle strength of elderly people. You put 200 old people on steroids, 200 old people on placebo, and 200 old people on no treatment. After one month, you measure the arm strength of each person. Which test should you use?
  4. You want to know whether a piece of bare copper wire in a bird bath will release enough dissolved copper to kill mosquito larvae. You go to a birdwatchers' club and find 32 people who each have two bird baths in their yard. You have them randomly choose one bird bath to put a piece of copper wire into. After a month, you go to each bird bath and count the number of mosquito larvae. Which test should you use?
  5. The wood thrush is a brown-and-white bird whose males sing when rival males get near their territory. You want to know whether the color of potential rivals affects how much male wood thrushes sing. You find a male wood thrush, then put a stuffed dead wood thrush on a stick near its territory. You record the number of calls the thrush makes in the next five minutes. You expose the same male wood thrush to a stuffed wood thrush whose white belly you have dyed a pale pink, and another stuffed wood thrush that you have dyed a lovely shade of pale blue, and record the calls of the live bird for the next five minutes each time. You expose the three dead and dyed birds to a total of 16 male wood thrushes. Which test should you use?
  6. You want to know whether the amount of light affects cell division in onion roots. You expose 20 onion plants to 20 different amount of light, from complete darkness to 100,000 lux (full sunlight). After one week, you dig up each onion plant, look at 250 cells from a root tip, and count the number of cells that are in interphase and the number of cells that are in the process of dividing (any stage other than interphase). Which test should you use?
  7. Carbon dioxide concentration in the atmosphere is increasing, and you want to know whether that will change the relative abundance of poison ivy in plant communities. You know that several people have done studies on this question, and you want to perform a meta-analysis to see if there's a general conclusion. Before you start collecting papers on the subject, what should you do?
  8. You want to know whether increased carbon dioxide in the air will make the stomata of a Tradescantia plant change size. You put a Tradescantia leaf under a microscope and measure the size of each of the 18 stomata in the microscope's field of view. You then increase the concentration of carbon dioxide in the room from 390 to 600 parts per million and measure the size of the same 18 stomata. Which test should you use?
  9. You've measured the amount of a particular protein on the surface of some cancer cells and some non-cancer cells. You calculate the mean and the standard error of the mean, and the cancer cells have a much larger standard error than the non-cancer cells. What are two possible reasons for the cancer cell data having a larger standard error (statistical reasons, not biological reasons)?
  10. You want to know whether the type of exercise affects the level of C-reactive protein, a protein associated with inflammation, in the blood. You get 7 groups of 50 volunteers each. Each group does one of the following exercises for 30 minutes a day: running, bicycling, swimming, Pilates, Zumba, weightlifting, or elliptical. After one week, you measure the C-reactive protein level in the blood of each person. What should you do next?
  11. When a male human sees someone attempting to kick him in his delicate groin area, he instinctively tries to block the kick with his knee. You want to know whether your younger brother is right-kneed or left-kneed. You attempt to kick him in the groin 17 times, and you record whether he blocks you with his right or left knee. Which test should you use?
  12. When grown in a lab, fruit fly (Drosophila melanogaster) larvae crawl out of the food to form a pupa. Some larvae pupate on the surface of the food, while other larvae crawl up the side of the container they are in and pupate on the side of the container. You want to know whether different mutants vary in the proportion of larvae that pupate on the surface of the food. You have four large containers, each with about 600 pupae; the first one has wild-type flies, the second has flies with the scalloped mutation, the third has flies with the singed mutation, and the fourth has flies with the sepia mutation. You count the number of pupae on the surface of the food and the number of pupae on the side of the container for each. Which test should you use?
  13. You are a sprinter, and you want to know the optimum amount of warmup running to do before you sprint. You know that if you don't warm up enough, you will feel stiff and run slowly. If you warm up the right amount, you will run faster. If you warm up too much, you will get tired and run slowly. For a month, you start every practice by running a randomly chosen warmup distance, ranging from 0 to 3000 meters; you then rest for two minutes, then time yourself as you run 100 meters as fast as possible. Which test should you use?
  14. You want to know whether diet affects the size of the appendix. You use MRI to measure the size of the appendix in 15 vegans, 20 vegetarians (who eat eggs and dairy, unlike the vegans), 17 people who eat fish but no birds or mammals, 12 people who eat fish and birds but no mammals, 21 people who eat everything except pork, and 30 people who eat everything. You apply the appropriate statistical test, and the result is significant--there is an overall effect of diet on appendix size. After you look at the data, you decide you'd like to know whether the difference in mean appendix size between vegans and vegetarians is signficant. Which test should you use?
  15. You want to know whether fluorescent lights cause cataracts in rats. You raise 20 rats under bright fluorescent lights for 24 hours a day for 6 months. Each rat has one eye covered with an eye patch. At the end of the experiment, you remove the lens from the covered and uncovered eye of each rat and measure the clarity of each lens at five randomly selected points. Which test should you use?
  16. You want to see whether there is an association between cell size and number of chloroplasts in cells of the water plant Elodea. You take digital images of about 20 Elodea cells. You arrange the images in order, from smallest to largest cells, then count the number of chloroplasts in each cell. Which test should you use?
  17. You run a salmon hatchery, and every day you measure the length of the salmon in a sample of 20 fish taken from each tank. You've been taking all 20 fish in each sample from just one dip of the net, but you've begun to worry that this may not give you an accurate estimate--maybe small fish swim around together and large fish swim around together, so one dip of the net is likely to get mostly small fish or mostly large fish, resulting in a lot of variation between netfuls of fish. So you dip the net into 10 random places in the tank and measure the length of 20 fish from each dip of the net. Which test should you use?
  18. Bone cells respond to mechanical stimulation by a rapid increase of intracellular calcium level. You want to test whether two types of bone cell (osteocytes and osteoblasts) respond differently to fluid shear stress. You stress 10 osteocytes and 10 osteoblasts, then stain the cells with a fluorescent dye that glows brighter green when more calcium is present. You take a picture of each cell and measure the intensity of green in each cell. Which test should you use?
  19. You want to know whether running causes knee osteoarthritis. You find 350 healthy female volunteers without knee osteoarthritis. Each keeps an exercise diary, recording how many miles a week they run. After two years you collect the exercise diaries, add up the total miles run for each woman, record the age and weight of each woman, and determine who has osteoarthritis. Which test should you use?
  20. You are studying the short-term effect of video games on blood pressure in young adults, in which you measure blood pressure before and after the volunteers play Frogger for 15 minutes. You measure the blood pressure 5 times before and after the video game for each of 10 volunteers. Which test should you use?
  21. You want to know whether a person's gaze affects their balance. You get 35 volunteers and time how long each one can stand on one foot while staring at a dot on the floor. You time the same people standing on one foot as they stare at a dot on the wall, at a dot on the ceiling, or out an open window. Which test should you use?
  22. You want to know the effect of tissue culture medium on the growth of prostate cancer cell lines. You buy tissue culture medium from three companies--Sigma, Invitrogen, and Fisher--and grow four cell lines on each medium. You grow 6 dishes of cells for each cell line in each medium. You analyze the data using the appropriate statistical test; the effect of culture medium has P=0.02, the effect of cell line has P=0.87, and the interaction term has P=0.30. How would you interpret these results?
  23. You want to know whether the amount of moisture you add to Drosophila food affects the survival of the flies. You make 2 vials of fly food with a different amount of water in each, one with 50 and one with 70% moisture content by weight. You put 50 fly eggs in each vial, wait three weeks, and count the number of live flies remaining in each vial. Which test should you use?
  24. You are planning a study of the size of weeping willow tree leaves in different habitats. You are trying to decide whether to sample a large number of trees in each habitat and measure a small number of leaves from each tree, or sample a small number of trees and measure a larger number of leaves per tree. You conduct a preliminary study in which you measure 50 leaves from each of 30 trees in one habitat. Which test should you use?
  25. You want to know whether singing affects the length of the uvula (the dangly thing that hangs down in the back of your mouth). You measure the length of the uvula of 85 professional singers, 123 people who sing once a week in church, and 132 people who never sing, with the exception of an occasional Happy Birthday. Which test should you use?
  26. Amphipod crustaceans (Talorchestia longicornis) burrow into the upper part of sandy beaches during the daytime. At night they emerge from their burrows, hop down toward the water, and eat seaweed. At dawn they hop back up the beach to burrow into the sand, well above the water line. You want to know whether they have a magnetic sense of direction. You capture 1500 amphipods at night and put them in the middle of round chamber with a level floor, no light, and sticky walls. You divide the chamber into four quadrants, north, south, east, and west. As dawn approaches, the amphipods hop to the edge of the chamber and get stuck, and you record how many are stuck to the edge of the chamber in each of the four quadrants. The next night, you repeat this with a new set of 1500 amphipods and a large magnet outside the chamber that overpowers the Earth's magnetic field. Which test should you use?
  27. You want to know whether female kangaroos jump farther when they don't have a baby in their pouch. You get 20 kangaroos carrying 10-week-old babies and measure the length of one jump for each kangaroo. You do the same for 20 kangaroos who are not carrying babies. Which test should you use?
  28. You want to know whether income affects dental health. You find 100 volunteers from northern Delaware, all around 40 years old, and ask them their annual income. You then have a dentist observe a picture of their teeth and gums and put them in order from worst to best. Which test should you use?
  29. You want to know which kind of soil is best for growing the new SweeTango variety of apples. You plant 10 SweeTango trees in an area of your orchard with loamy soil, 10 in an area with sandy soil, 10 in an area with clay soil, and 10 in an area with silty soil. After the trees grow for four years, you count the number of apples each tree produced. Which test should you use?
  30. You're planning a study to see whether polar bears in the Arctic National Wildlife Refuge, where no oil drilling is allowed, are fatter than polar bears in the Prudhoe Bay area, where there are oil wells and pipelines. It's a lot of work to find a polar bear, tranquilize it, and weigh it. You've decided that you want to be able to detect a 25-kg difference in mean weights with a significance level of 0.05. What other information do you need to determine the number of bears you'll need to catch?

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