Lichens show symbiotic relationship between
A. Fungus and roots of higher plants
B. Fungus and algae
C. Two algae
D. Two fungi

Hint: It takes a long time for Lichens to develop and grow. Some are considered the oldest living species on the earth. Lichens are known as sensitive air pollution indicators, particularly for sulphur dioxide.

Complete Answer:
- Lichens are created by the interaction between two species, algae and fungi. The colour of the lichen is determined by the algae it contains. Lichen is not a single organism; it is a stable symbiotic relationship between fungi and algae and/or cyanobacteria.
- As all fungi, lichen fungi need carbon as a food source; this is provided by their symbiotic algae and/or cyanobacteria, which are photosynthetic.
- Lichen symbiosis is considered to be mutualism, since it supports both the fungi and the photosynthetic allies, called photobionts.
- Many unrelated and very different fungi form lichens, like mushroom-forming fungi and, in particular, cup-fungi. 98% of lichen fungi are cup-fungi or ascomycetes. Totally half of all ascomycetes and one in five of all recognized fungi form lichens.
- Lichenification is an ecological strategy or a popular mode of nutrition among unrelated fungi.
- Lichens are made up of two or more species, a fungus, and one or more partners, called photobionts, that interact closely. The photobiont may be algae and/or cyanobacteria, all of which, through photosynthesis, may produce simple sugars. Fungi, by comparison, are 'heterotrophic' and need an external food source.
- The fungi create the lichen thallus structure, inside which they provide the basis of the lichen symbiosis with conditions for a long-term , stable relationship with their photobionts.

The correct Answer is option (B) Fungus and algae.

Note: 400 genres and 15,000 species of lichens are there in the world.Bark of the trees , bare rocks and logs of wood that are dry are the growth place of lichens.Being xerophyte in nature they can withstand drought conditions.