In 1979, an accident happened at the Three Mile Island nuclear power plant in Pennsylvania. Through a combination of mechanical failure and human error, cooling water drained from the reactor ves-sel, temperatures rose inside the reactor core, and metal surrounding the uranium fuel rods began to melt, releasing radiation. This partial meltdown proceeded through half of one reactor core. Area residents stood ready to be evacuated. For-tunately, however, most radiation remained trapped inside the building that contained the nuclear reac-tor. The accident was brought under control within days. The damaged reactor was shut down. It took years, and about a billion dollars, to clean up the damage.

16. Which of the following best describes the sequence of events at Three Mile Island?a. partial meltdown, followed by loss of cooling water, followed by rising temperatures in the reactor coreb. partial meltdown, followed by the release of radiation, followed by an explosionc. partial meltdown, followed by cleanup, fol-lowed by rising temperatures in the reactor cored. loss of cooling water, followed by rising temperatures in the reactor core, followed by partial meltdown

17. People were not evacuated becausea. the cleanup had begun. b. most of the radiation did not leak out. c. the evacuation would have cost billions of dollars. d. only one reactor was affected.

18. Which of the following was NOT involved in the accident at Three Mile Island?a. an explosionb. reactor damagec. nuclear fissiond. mistakes by people

Two male mice, which we will call male a and male b, are both phenotypically normal. male a was from a litter that contained half phenotypically normal mice and half dwarf mice. the mother of male a was known to be homozygous for the normal igf2 allele. male b was from a litter of eight mice that were all phenotypically normal. the parents of male b were a phenotypically normal male and a dwarf female. male a and male b were put into a cage with two female mice that we will call female a and female b. female a is a dwarf and female b is phenotypically normal. the parents of these two females were unknown, although it was known that they were from the same litter. the mice were allowed to mate with each other, and the following data were obtained: female a gave birth to three dwarf babies and four normal babies. female b gave birth to four normal babies and two dwarf babies. which male(s)mated with female a and female b? male a with both females male a with female b, and male b with female a male a with female a, and male b with female b could not be determined male b with both females

Experiments in environmental toxicology can sometimes be manipulative experiments in which the researcher actively chooses and manipulates the independent variable. in hunt's study, for example, dosages of bpa were manipulated and the effects were measured. in manipulative studies, the researcher controls all the other variables in the experiment, so any health effects observed in the test subjects can be attributed to differences in the independent variable. in other cases, researchers use natural experiments in which the dependent variable (typically a measure of organism health) is measured under differing contexts that are not manipulated. say, for example, that an accidental chemical spill contaminates five ponds. to determine the possible effects of the toxic chemical on frogs, a researcher could compare the hatching rate of frog eggs laid in those five ponds to the hatching rate of eggs laid in five uncontaminated ponds nearby. this would be an example of a natural experiment because concentrations of the toxic chemical in the ponds were not controlled by the experimenter, but rather resulted from the chemical spill. drag type of experiment on the left to the example of experiment on the right. blood concentrations of bpa in college students are compared to their recent manipulative consumption of canned food items 2. the feeding behavior of fish in streams that receive acidic runoff from strip mines is compared to the feeding behavior of fish in unaffected streams. the deformity rate in baby birds from nests in pesticide-sprayed fields is compared to the deformity rate in birds from nests in unsprayed fields 4 tumor development is compared in mice exposed to five dosages of a known carcinogen in the laboratory foraging activity levels are compared in tadpoles exposed to four concentrations of toxic metals in the laboratory. growth of corn plants is compared in field plots sprayed with three different dosage: s of weed killer 7 bpa concentrations in the urine of people with diabetes are compared to bpa concentrations in the urine of people without diabetes - natural; manipulative

Many plants can reproduce asexually. which of these is an example of asexual reproduction in a plant? a. pine cones forming on a tree b. cross-pollination in a tomato c. roots sprouting from a potato d. night-blooming jasmine flowers