Ciall amhain is ea an proiseas chun muciarann (le tiuchan ard carboin) a mhalartu ina iarann saoirsithe (le tiuchan an-iseal carboin) trina lea i bhfoirneis bheag ina n-oibritear e chun an carbon a bhaint as tri ocsaidiu leis an aer, agus an tslaig a bhaint tri easbhru. Dheantai e seo leis na lamha, ach deantar go meicniuil anois e. Ciall eile is ea corrai meascan coincreite chun siothlu a chur ar aghaidh is comhdheanamh aonfhoirmeach a bhaint amach. [1]