Test: Virus - 1 - NEET MCQ

Tobacco mosaic virus is a Plant virus and mostly plant viruses have single stranded RNA  as their genetic material. 

Viruses are obligate parasites. In addition to proteins, viruses also contain genetic material, that could be either RNA or DNA. No virus contains both RNA and DNA.

. In general, viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or double stranded DNA

• Mumps is a viral infection caused by the mumps virus.
• Mumps is extremely infectious and spreads quickly to people living nearby.
• The virus is spread through respiratory droplets or through direct contact with an infected human.
• It mainly affects salivary glands in the region of our ears and can cause inflammation in one or both of these glands. Mumps affect the parotid glands, the salivary glands behind and in front of the ears.
• When contracting mumps, the virus travels from the respiratory tract to the salivary glands and reproduces, causing the glands to swell.

• Tobacco mosaic virus (TMV) is a positive-sense single stranded RNA virus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae.
• The infection causes characteristic patterns, such as "mosaic"-like mottling and discoloration on the leaves.

• Viruses were not included in Whittaker's five kingdom classification because they lack cellular structure.
• Viruses are non-cellular and consist of genetic material (either RNA or DNA) enclosed in a protein coat.
• They are considered obligate parasites and cannot replicate on their own.

Dmitri Ivanowsky was the scientist who recognized certain microbes as the causal organism of the mosaic disease of tobacco. These were found to be smaller than bacteria because they passed through bacteria-proof filters

Virus means venom or poisonous fluid.

. Viruses did not find a place in classification since they are not considered truly ‘living’, if we understand living as those organisms that have a cell structure. The viruses are non-cellular organisms that are characterised by having an inert crystalline structure outside the living cell. W.M. Stanley (1935) showed that viruses could be crystallised and crystals consist largely of proteins. They are inert outside their specific host cell. Viruses are obligate parasites.

W.M. Stanley demonstrated that viruses could be crystallized, with these crystals primarily consisting of proteins. This groundbreaking discovery provided insights into the structural composition of viruses and their behavior outside their specific host cells. Stanley's work significantly contributed to the understanding of viruses as obligate parasites and highlighted the importance of their proteinaceous nature in their biological activities.

 In 1971, T.O. Diener discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease. It was found to be a free RNA; it lacked the protein coat that is found in viruses, hence the name viroid. The RNA of the viroid was of low molecular weight.

Ivanowsky - Recognized tobacco mosaic is caused by microbes smaller than bacteria

Beijerinek- Demonstrated extract of infected tobacco plants could cause infection in healthy plants

Stanley- Showed that viruses could be crystallized

so answer (A)

The correct option is C

Assertion [A] is True and Reason [R] is True and is a correct explanation for [A].

Viruses are very small organisms which contain genetic material (DNA or RNA) and a protein coat covering it. A cellular structure is absent. Therefore viruses depend on the host for their survival. Viruses cannot survive outside the host. They can also be crystallised, which is a property of non-living things. This is the reason why they are considered to be at the borderline of living and non-living things.

Bacterial viruses or bacteriophages (viruses that infect the bacteria) are usually double stranded DNA viruses

The protein coat  of virus is called capsid made of small subunits called capsomeres, protects the nucleic acid. These capsomeres are arranged in helical or polyhedral geometric forms.