The question addressed in the title was examined by measuring fluorescence emission spectra and light-induced fluorescence-yield changes of chloroplasts which had been frozen to -196 degrees C rapidly, as very thin samples adsorbed into substrates whick were plunged directly into liquid nitrogen, or slowly by the cooling action of liquid nitrogen through the wall of the cuvette. Contrary to previous reports, we found that the rate of cooling had no influence on the shape of the emission spectrum, the extent of the variable fluorescence or the fraction of the absorbed quanta which are delivered initially to Photosystem I.