<P> Cyanobacteria possess carboxysomes, which increase the concentration of CO around RuBisCO to increase the rate of photosynthesis . An enzyme, carbonic anhydrase, located within the carboxysome releases CO from the dissolved hydrocarbonate ions (HCO). Before the CO diffuses out it is quickly sponged up by RuBisCO, which is concentrated within the carboxysomes . HCO ions are made from CO outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein . They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO very slowly without the help of carbonic anhydrase . This causes the HCO ions to accumulate within the cell from where they diffuse into the carboxysomes . Pyrenoids in algae and hornworts also act to concentrate CO around rubisco . </P> <P> The overall process of photosynthesis takes place in four stages: </P> <Table> <Tr> <Th> Stage </Th> <Th> Description </Th> <Th> Time scale </Th> </Tr> <Tr> <Td> </Td> <Td> Energy transfer in antenna chlorophyll (thylakoid membranes) </Td> <Td> femtosecond to picosecond </Td> </Tr> <Tr> <Td> </Td> <Td> Transfer of electrons in photochemical reactions (thylakoid membranes) </Td> <Td> picosecond to nanosecond </Td> </Tr> <Tr> <Td> </Td> <Td> Electron transport chain and ATP synthesis (thylakoid membranes) </Td> <Td> microsecond to millisecond </Td> </Tr> <Tr> <Td> </Td> <Td> Carbon fixation and export of stable products </Td> <Td> millisecond to second </Td> </Tr> </Table> <Tr> <Th> Stage </Th> <Th> Description </Th> <Th> Time scale </Th> </Tr>

Plants release oxygen gas a by-product of photosynthesis. oxygen gas produced from