Beyond Single Cell: Viruses, Viroids and Lichens

Cellular classification provides a framework for understanding life, but exceptions exist. This section explores viruses and viroids, entities blurring the lines between living and non-living. Viruses, obligate parasites, require a host cell for replication, while viroids, even simpler, are infectious RNA molecules dependent on plants.

Deviation from Basic Cell Types

• Virus(means poisonous fluid): These are obligate parasites inert outside their specific host cell.
• Virions: The main difference between a virus and a virion is that a virus is the nucleoprotein particle, whereas a virion is the active, infectious form of the virus.
• Viroids: These are infectious agents that consist only of naked RNA without any protective layer, such as a protein coat.
  • These infect plants (but no other forms of life) and are replicated at the expense of the host cell.
  • Viroid genomes are small single-stranded circles of RNA that are only 250–400 bases long.

• Lichens: Lichens are symbiotic associations (mutually useful associations) between algae and fungi.
  • The algal component is known as phycobiont, and the fungal component is mycobiont, which are autotrophic and heterotrophic, respectively.
  • Algae prepare food for fungi, and fungi provide shelter and absorb mineral nutrients and water for their partners.
  • Lichens are very good pollution indicators- they do not grow in polluted areas.

Difference between Positive-sense single-stranded and Negative-sense single-stranded RNA viruses

Conclusion

Beyond single cells, fascinating partnerships emerge. Lichens, a symbiotic association of algae and fungi, exemplify this intricate dance. Understanding these deviations from basic cell types broadens our knowledge of the diverse and interconnected web of life on Earth.

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