The given blank can be filled with External.
The stimulus is a physical entity, which can provoke the response in the body of an organism. The hiding of the organism under the rock in response to the predator is and a type of external stimuli, as in this case, the organisms hide themselves inside the rock in response to the predator, which is present outside the body of the organism.
In this zone, the intensity of light rapidly dissipates as depth increases. Such a minuscule amount of light penetrates beyond a depth of 200 meters that photosynthesis is no longer possible. The aphotic, or “midnight,” zone exists in depths below 1,000 meters (3,280 feet).
In order to support the hypothesis that mutations occur in response to an environmental challenge, the experiment in question would have to show an increase in mutation rates shortly after the environmental challenge was introduced.
When we test a hypothesis, we perform an experiment and gather data over the course of the testing. In order to obtain evidence that supports a hypothesis, we have to ensure that only one variable is changing and be sure to repeat the experiment to confirm the values measured.
Taking this into account, a hypothetical result of the fluctuation test that would support the hypothesis of mutations in reaction to environmental challenges would be to measure a spike in mutation rates in the generation following an environmental challenge, and then continue to do so with future post-challenge generations.
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