This update discusses the physiological roles of carbonic anhydrase (CA) in plants and algae. It examines some new observations about the functions and assumed functions of CA in plants and algae. Specifically, CA does not regulate pH within plant cells as in blood, which has a high CO2 concentration. Nor do the chloroplast CAs help deliver CO2 to Rubisco during C3 photosynthesis in plants. However, CAs are essential to plants and algae. An under-appreciated function of CA is supplying bicarbona