Final answer:
Lichens are in symbiosis with both cyanobacteria and green algae (D) A and B). In this symbiotic relationship, the photosynthetic partners provide carbohydrates and sometimes fix nitrogen, while the fungus offers protection and anchorage.
Step-by-step explanation:
Lichens represent a symbiotic relationship between a fungus and a partner that can perform photosynthesis, which can be a green alga or cyanobacterium. The direct answer to the question is D) A and B, indicating that lichens are in symbiosis with both cyanobacteria and green algae.
In these associations, the photosynthetic partner provides organic carbon and energy in the form of carbohydrates, while some cyanobacteria can also fix atmospheric nitrogen, benefiting the lichen by adding nitrogenous compounds. The fungal partner, in turn, provides minerals, protection from desiccation and excess light, and helps anchor the lichen to its substrate.
This relationship often allows the lichen to inhabit harsh environments that neither partner could withstand alone. Nonetheless, it's worth mentioning that this symbiosis is sometimes considered to be a form of controlled parasitism, where the fungus may benefit more than the algae or cyanobacterium.