The effects of varied temperature on membrane potential difference (p.d.) and resistance were measured in single cells of the green, fresh water alga Ohara oorallina and the red, marine alga Griffithsia pulvinata. The effects of varied temperature on membrane potential difference (p.d.) and resistance were measured in single cells of the green, fresh water alga Ohara oorallina and the red, marine alga Griffithsia pulvinata.