What are the characteristics of virus,viroids,lichens?

Viruses are crystalline, non living organisms which are obligate parasites. They need a host for replication. They lack most metabolic machineries. The viruses can only have DNA or RNA as their genetic material. Some of the deadliest diseases are caused by viruses.

 

Viroids are virus particles without the external protein coat. They have low molecular weight.They are mostly plant pathogens. Potato spindle tuber disease is caused by a viroid. 

 

Lichens are symbiotic association between algae and fungi, where the algae produces food and fungi provides shelter, water and minerals. Lichens are good indicators of pollution as they do not grow in polluted areas. They also play a very important role in ecological succession.

 

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