A. Fluorescent molecules have what are known as fluorescence
lifetimes. The lifetime is the time the fluorophore spends in the
excited state or the time between when it is first excited and when
it emits light. Typically fluorescence lifetimes are around a
nanosecond. In theory then a single fluorescence molecule could
emit how many photons during a second. Given this property of
fluorophores and the design of a fluorescent microscope explain why
fluorescence is such a sensitive means of detection.

B. What is the lowest number of protein molecules that can be
detected by fluorescence?