What in an experiment is unchanged but used to compare your results to?

A control set up
it's a set up without the factor tested hence is unchanged. you compare you results to it so show that no external factors were the cause of your results and the change is purely due to the factor tested.

This is what i found on google “phytoplankton, tiny organisms that live in the ocean, are autotrophs. some types of bacteria are autotrophs. most autotrophs use a process called photosynthesis to make their food.” i hope this you for what your looking for

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