The algal partner of lichen is known as phycobiont while the fungal partner is known as mycobiont. While the phycobiont provides food to the mycobiont, the mycobiont provides protection to the phycobiont.
Through http://wiki.answers.com/topic/photosynthesis the algal cells provide simple sugars and vitamins for both partners in this symbiotic association. The fungal cells protect the algal cells from...