Viroids Viruses and Bacteria – Easy way to learn

Viroids, Viruses and Bacteria are classified as Microbes. Generally, Microbes are living organisms that can’t be visible through the naked eye. in this post, we will learn all the important points of them.

viroids virus and bacteria
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  • Viruses did not find a place in classification since they are not truly ‘living’ if we understand living as those organisms that have a cell structure.
  • Viruses are non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell.
  • Viruses are obligate parasites. Once they infect a cell, they take over the machinery of the host cell to replicate themselves, killing the host.
  • The name virus which means venom or poisonous fluid was given by Pasteur.
  • In addition to proteins, viruses also contain genetic material, which could be either RNA or DNA.
  • No virus contains both RNA & DNA.
  • In general,
    • viruses that infect plants have single-stranded RNA &
    • viruses that infect animals have either single or double-stranded RNA or double-stranded DNA
    • bacteriophages (viruses that infect bacteria) are usually double-stranded DNA viruses.
  • The protein coat called capsid made of small subunits called capsomeres protects the nucleic acid.
  • These capsomeres are arranged in helical or polyhedral geometric forms.

Types of Viruses

  • Viruses cause diseases like mumps, smallpox, herpes & influenzaAIDS is also caused by a virus.
  • In plants, the symptoms can be mosaic formation, leaf rolling & curling, yellowing & vein clearing, dwarfing & stunted growth.


  • Viroids are infectious agents that are smaller than viruses.
  • A viroid is a free RNA, it lacks the protein coat that is found in viruses, hence the name viroid.
  • The RNA of the viroid was of low molecular weight.
  • Viroids cause potato spindle tuber disease.

Difference between Viroids and Viruses

It is a nucleoprotein particle.It is an RNA Particle.
Nucleic Acid can be DNA or RNA.Viroid is formed of only RNA.
A protein covering of coat is present.A protein coat is absent.
Virus has a larger size.Viroid has a smaller size.
Virus infects all types of organisms.Viroid infects only plants.
difference between viroids and viruses


  • Bacteria are single-cell, living organisms that can survive without a host.
  • They can live on surfaces, in soil, in water, & in the air.
  • You can kill them by messing with their ability to do cellular respiration or their ability to grow.
  • Antibiotics are used to treat bacterial infections because antibiotics kill bacteria.
  • Hence Antibiotics are useless against viruses.
  • There are some antiviral drugs that help protect you from a viral infection.
  • Antivirals either make it harder for the virus to get into the cell or they prevent the virus from reproducing once they are inside of your cells. 
  • Most bacteria reproduce by simply dividing into two.
  • Bacteria can cause diseases such as pneumonia & food poisoning.
  • However, not all bacteria are bad. In fact, some friendly types actually help protect us from the disease.

Difference between Bacteria and Viruses

They are very SmallThey are larger in size as compared to virus
Have no metabolism of their ownHave metabolism of their own
Take no food by any methodTake food by absorption
Do not grow & do not divideGrow in size & divide to produce more bacteria (by Cell-Division)
Command the host cell to produce virusThey can reproduce by their own
Can be crystallisedCannot be crystallised
All produce diseases in man, animals & plantsSome are harmless, some useful & some are disease-causing
Contains only genetic material & protective coatingContains various cells subunits or organelles such as cytoplasm & cell wall which all perform specific functions
They have simpler DNA (if their genetic material is DNA)They have more complex DNA
Multiply faster than bacteriaMultiply slower than Viruses
They are Non-LivingThey are living
Vaccines prevent the spread & antiviral medicines help to slow reproduction but cannot stop it completelyThey can be treated with Antibiotics
Example– Common Cold, Flu & Sore ThroatExample– Strep Throat, Tuberculosis, Whooping Cough

Difference between DNA and RNA Viruses

DNA VirusesRNA Viruses
these types of viruses contain DNAcontain RNA
DNA replication takes place in the nucleusRNA replication takes place in the cytoplasm
more stableunstable

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Last updated: August 20, 2023 Updated on 10:13 AM