Chlorella is explicitly described as a unicellular alga rich in proteins, used as a food supplement . In contrast, Volvox is described as a colonial form . Gelidium and Gracilaria are red algae used to produce Agar , and most red algae are multicellular . Laminaria and Sargassum are brown algae which can form massive plant bodies . Therefore, the pair containing the unicellular alga Chlorella is the correct answer.