Texts: Read the following passage then match the sentence or sentence fragments with the element of the experimental design chosen to test the hypothesis. Choose the best answer. A biologist notes that frogs from several ponds in the upper midwestern USA have more than two hind limbs, also known as polydactyly. After dissection, the scientist finds parasitic flatworms in the frogs' tissues. The scientist thinks that perhaps the parasite is causing the frogs to grow extra legs during development. If parasites are causing polydactyly in the frogs, then the incidence of polydactyly is expected to be much greater in frogs reared with parasitic infections than frogs reared parasite-free. The scientist sets up two captive frog populations, and in only one does he infect the frogs with parasites so he can compare the number of frog offspring that have extra limbs in the two populations. The researcher ensures similar terrestrial and aquatic habitat parameters exist in the two captive populations, such as temperature, pressure, salinity, and feeding regime. After testing, the scientist observes that 90% of the offspring from the parasite-infected population develop additional limbs, whereas only 3% of offspring from the parasite-free population develop additional limbs. The scientist is now more confident that the parasite is somehow causing frogs to grow additional limbs. Experimental Variable: The incidence of polydactyly Dependent Variable: [Choose] Standard/Controlled Variables: [Choose] Experimental Group: [Choose] Control Group: [Choose]

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