Jenny was worried about how some pollutants in a lake near her home were affecting the levels of dissolved oxygen in the water, so she designed the following experiment.
First, she collected five 10-gallon aquariums and filled each with water from her tap. Then, she tested the initial oxygen level of the
tap water.
Next, she put a tablespoon of different pollutants, including gasoline, cooking oil paint, and lawn fertilizer, in each of four of the
tanks. She stirred those four tanks for 1 minute each to help the pollutant dissolve or spread out in the tank.
Finally, she tested the oxygen level in each tank once every hour and recorded her results in the table below.
Tank
Pollutant
in water
Initial
O2 level
(without pollutants)
O2 level O2 level
after 1 hour after 2 hours
1 none
2 gasoline
3 cooking oil
4 paint
5 lawn fertilizer
What is the dependent variable in Jenny's experiment?
OA. initial oxygen level in tank without pollutant
OB. levels of Oz in each tank
OC. amount of pollutant put in each tank
OD. pollutant in each tank

Enzymes are proteins that speed up reactions by providing an additional energy source supplying additional molecules for the reaction removing inhibitors that slow down reactions lowering the amount of energy required

Researchers randomly divide participants into groups. each group takes a different amount of omega-3 fatty acid supplements daily for a month. one group receives a placebo. the researchers measure the impact on cholesterol levels in the blood. what is the purpose of random assignment in this experiment? a, to produce treatment groups with similar characteristics b, to ensure that all people with high cholesterol have an equal chance of being selected for the study c, to increase the accuracy of the research results and prevent skewness in the data

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