Chapter 2: Biological Classification

Ans: Virus (L. toxic fluid) is a category of ultramicroscopic, non-cellular, extremely infectious organisms that reproduce exclusively intracellularly — within the living host cells – without the need for growth or division. They are inert particles outside of the host cells. They are nucleoproteins that have one or more nucleic acid molecules, such as DNA or RNA, enclosed in a protein or lipoprotein sheath. The nucleoid (genome) and capsid are the two sections of a virus. In some circumstances, an envelope and a few enzymes are present.

• Nucleoid: The viral chromosome is represented by the nucleoid, which is a nucleic acid found in the virus. It is made of a single nucleic acid molecule. It might be linear or circular, using DNA or RNA as the nucleic acid. It is the section of the virus that uses the host cell's metabolic machinery to synthesize and assemble viral components.

• Capsid: It's a protein that encases genetic material. Capsomeres are protein components found in capsids. The nucleoid is protected by the capsid from physical and chemical agents.

• Envelope: The envelope is a loose outer covering seen on some viruses, such as animal viruses (e.g., HIV), but not on plant or bacterial viruses. It is made up of viral protein, as well as lipids and carbohydrates from the host. Spikes, or outgrowths, may be present. Peplomers are components of envelope proteins. A virus that does not have an envelope is known as a naked virus.

Influenza, polio, measles, chickenpox, hepatitis, AIDS, bird flu, SARS (Severe Acute Respiratory Syndrome), and other viral infections are common.

Ans: Viruses are thought to be a bridge between non-living and living things. It's tough to tell whether they're alive or dead. Viruses have some characteristics that indicate their non-living nature, while others indicate their alive nature.

They have the appearance of non-living items.

• Protoplast deficiency.

• Crystallization ability.

• Inability to live without the assistance of a living cell.

• A high specific gravity that can only be found in non-living things.

• The inability to breathe.

• The lack of an energy storage system.

• Lack of division and development. Different sections are synthesized independently instead.

Viruses are similar to living organisms in that they are made up of organic macromolecules that are only found in living organisms.

• Genetic material is present.

• The ability to multiply or reproduce, but only inside the confines of a live cell.

• Mutation occurrence.

• Enzyme transcriptase is found in the majority of viruses.

• Vitamins such as riboflavin and biotin are found in some viruses, such as the Pox virus.

• Autoclaving and ultraviolet light both ‘kill' viruses.

• They reproduce by Penicillium type. Even variances can be passed on.

• They take over the host cell's biosynthetic machinery and manufacture substances necessary for their replication.