Agar-agar, a gelatin like substance, is obtained commercially from the red algae, eg, Gelidium and Gracilaria. It is: used widely in preparing solid food media for the growth of bacteria or fungi in laboratory.
An antibiotic chlorellin is obtained from Chlorella. Chlorella is also a good source of proteins and Vitamins. It is also used in space travel as it is able to utilize all the CO2 released by the astronauts and provides O2 and food required by space travellers.