What does a fluorometer measure in GFP studies?

In studies involving Green Fluorescent Protein (GFP), a fluorometer is primarily used to measure the fluorescence emitted by GFP when it is excited by a specific wavelength of light. When GFP is subjected to this excitation light, it absorbs energy and subsequently re-emits light at a longer wavelength. This property is fundamental to the use of GFP as a fluorescent marker in biological research and allows researchers to quantify the amount of GFP present in a sample.

Understanding fluorescence emission is crucial for applications such as monitoring protein localization, studying gene expression, and analyzing cellular processes. By measuring the intensity of the emitted fluorescence, researchers can derive information about the concentration of GFP in the sample, how it's distributed within cells, and its overall biological activity. Thus, the correct answer highlights the core function of a fluorometer in the context of GFP studies.