By Team Aakash Byju's
Viruses are obligate non-cellular parasites characterised by the presence of an inert crystalline structure outside the living cell.
Once a cell has been infected by a virus, the virus kills the host cell and uses its machinery to replicate itself.
Diseases including mumps, smallpox, herpes, influenza, and AIDS are caused by viruses.
Viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or DNA.
Viroids are smaller than viruses, found to have free RNA. They lack the protein covering found in viruses, hence the term viroid.
They affect only the plants and are therefore known as plant pathogens. Citrus exocortis, cucumber pale fruit are a few plant diseases caused by viroids.
Prions are infectious organisms that cause several neurological disorders in mammals.
They can degrade nucleic acids but are sensitive to chemicals that denature proteins.
Prions are quite rare and difficult to transmit. Creutzfeldt-Jakob Disease,Variant Creutzfeldt-Jakob Disease are a few diseases caused by prions.
Lichens are symbiotic connections between fungi and algae. The majority of the lichen is composed of the fungus and the rest is made up of a green or blue-green alga.
Algae produce food, while the fungus provides protection and absorbs mineral nutrients.
Beard lichen, Dog lichen, Iceland moss, Oak moss, etc are a few examples of Lichens.