Biological Classification – VIRUSES, VIROIDS, PRIONS AND LICHENS - NEET Biology MCQs (Part 12)

Correct Answer: A

In R.H. Whittaker’s five kingdom classification system, organisms are grouped into Monera, Protista, Fungi, Plantae and Animalia. However, lichens and some acellular entities such as viruses, viroids and prions are not included in this classification. Lichens are symbiotic associations of algae and fungi, while viruses, viroids and prions are considered non-cellular infectious agents.

Correct Answer: C

Common cold and influenza (flu) are viral infections that affect the human respiratory system. Viruses are microscopic infectious agents that invade host cells and use the host's cellular machinery to reproduce. Once inside the body, viruses multiply rapidly and cause symptoms such as sneezing, coughing, fever and weakness. Because viruses are not cellular organisms, they are not included in Whittaker’s five kingdom classification.

Correct Answer: B

Viruses are not included in Whittaker’s five kingdom classification because they do not possess a cellular structure. Living organisms are generally defined as those having cells with organized cellular components. Viruses lack this cellular organization and exist as particles made of genetic material surrounded by a protein coat. Because of this unique nature, they are not considered truly living organisms in the traditional sense.

Correct Answer: A

Viruses are not included in the classification of living organisms because they do not possess cellular organisation. Living organisms are defined as those that have a cellular structure with metabolic activities. Viruses lack this cellular structure and cannot perform metabolic functions independently. They behave like non-living particles outside a host but show characteristics of living organisms only when they infect host cells and replicate.

Correct Answer: B

Viruses are non-cellular organisms that behave like non-living particles outside a host cell. In this state they may even form an inert crystalline structure. However, when they enter a living host cell, they become active and start replicating using the host's cellular machinery. Because of this dual nature, viruses are considered to lie at the boundary between living and non-living organisms.

Correct Answer: B

Viruses cannot reproduce independently because they lack cellular machinery. When a virus enters a host cell, it takes control of the host's metabolic and genetic machinery. The host cell then begins producing many copies of the virus. This process is called replication. Often, the host cell is damaged or destroyed during this process, which can lead to disease in the infected organism.

Correct Answer: B

The term 'virus' comes from a Latin word that means venom or poisonous fluid. Early scientists used this term because viral infections were thought to be caused by poisonous substances present in infected materials. Later, with the development of microscopy and molecular biology, viruses were identified as microscopic infectious agents that replicate only inside living host cells.

Correct Answer: C

In 1892, the Russian scientist Dmitri Ivanowsky studied the mosaic disease of tobacco plants. He discovered that the infectious agent causing the disease could pass through bacteria-proof filters. This observation suggested that the disease was caused by an extremely small infectious particle smaller than bacteria. Later studies identified this agent as a virus, now known as the Tobacco Mosaic Virus (TMV).

Correct Answer: B

Early scientists discovered that the infectious agents causing diseases like tobacco mosaic disease could pass through bacteria-proof filters. Since bacteria were trapped by these filters, the infectious particles that passed through had to be smaller than bacteria. These particles were later identified as viruses, which are extremely small infectious agents.

Correct Answer: B

In 1898, the scientist M.W. Beijerinek demonstrated that the extract from tobacco plants infected with mosaic disease could infect healthy plants. He concluded that the causative agent was not a bacterium but a new type of infectious particle. He named this pathogen 'virus' and described it as Contagium vivum fluidum, meaning 'infectious living fluid'. This discovery was an important step in the understanding of viruses.

Correct Answer: C

In 1935, the scientist W.M. Stanley successfully crystallised the Tobacco Mosaic Virus (TMV). This experiment showed that viruses could exist in a crystalline form outside living cells. Stanley also demonstrated that these crystals consisted largely of proteins. His work provided important evidence about the chemical nature of viruses and helped advance the scientific understanding of viral structure.

Correct Answer: B

Viruses are considered inert or inactive outside their specific host cells because they cannot carry out metabolic activities or reproduce on their own. They lack the cellular machinery needed for life processes. However, once they enter a suitable host cell, they become active and use the host cell's machinery to replicate and produce new virus particles.

Correct Answer: A

Viruses are called obligate parasites because they can reproduce only inside the living cells of a host organism. They do not have their own metabolic machinery to grow or replicate independently. Therefore, they depend completely on the host cell's machinery for replication and survival.

Correct Answer: B

Viruses are called obligate parasites because they cannot carry out life processes independently. They lack cellular machinery needed for metabolism and reproduction. Therefore, viruses must enter a living host cell and use the host’s metabolic and genetic machinery to replicate and produce new virus particles. Outside the host cell they remain inert and inactive.

Correct Answer: B

Viruses contain genetic material that may be either DNA or RNA, but not both at the same time. This genetic material is enclosed within a protein coat called a capsid. The nucleic acid carries the information required for replication of the virus inside a host cell. Some viruses such as bacteriophages contain DNA, while others such as the influenza virus contain RNA.

Correct Answer: C

Viruses contain genetic material that may be either DNA or RNA, but never both at the same time. This nucleic acid carries the genetic information required for viral replication inside the host cell. The genetic material is enclosed within a protein coat called a capsid. Depending on the virus, the genome may be single-stranded or double-stranded DNA or RNA.

Correct Answer: A

A virus is basically a nucleoprotein particle. It consists of genetic material (DNA or RNA) surrounded by a protein coat called capsid. The nucleic acid carries the genetic information needed for replication, while the protein coat protects it. Because of this structure, viruses are described as nucleoprotein particles.

Correct Answer: A

Most plant viruses contain single-stranded RNA as their genetic material. This RNA carries the information required for the virus to replicate inside plant cells. A well-known example is the Tobacco Mosaic Virus (TMV), which infects tobacco plants and causes mosaic disease. Plant viruses typically spread through mechanical injury, insect vectors or infected plant material.

Correct Answer: A

Animal viruses show greater diversity in their genetic material compared to plant viruses. They may contain single-stranded RNA, double-stranded RNA or double-stranded DNA as their genetic material. These nucleic acids carry the genetic information required for viral replication inside the host animal cells. Examples include influenza virus (RNA virus) and adenovirus (DNA virus).

Correct Answer: B

Bacteriophages are viruses that infect bacterial cells. In most bacteriophages, the genetic material is double-stranded DNA. When a bacteriophage infects a bacterial cell, it injects its DNA into the host cell and uses the bacterial machinery to replicate and produce new virus particles. Bacteriophages play an important role in bacterial genetics and molecular biology.

Correct Answer: A

The protein coat surrounding the genetic material of a virus is called the capsid. The capsid protects the viral nucleic acid (DNA or RNA) and helps the virus attach to host cells. It is made up of many smaller protein subunits called capsomeres. Together, these capsomeres assemble to form the capsid structure that encloses the viral genome.

Correct Answer: A

Capsomeres are the small protein subunits that form the viral capsid. These capsomeres are arranged in definite geometric patterns to form the protective coat around the viral nucleic acid. The two common arrangements are helical and polyhedral structures. These organized structures help protect the genetic material and maintain the shape of the virus.

Correct Answer: A

Many human diseases are caused by viruses. Examples include mumps, smallpox, herpes and influenza. Viruses are microscopic infectious agents that replicate only inside living host cells. When they infect the body, they interfere with normal cellular functions and cause various symptoms and diseases.

Correct Answer: C

AIDS (Acquired Immunodeficiency Syndrome) in humans is caused by a virus called HIV (Human Immunodeficiency Virus). This virus attacks the immune system, especially the CD4 T-lymphocytes, weakening the body's ability to fight infections and diseases. As the immune system becomes severely damaged, the person becomes vulnerable to many opportunistic infections.

Correct Answer: D

Viral infections in plants produce several characteristic symptoms. These include mosaic patterns on leaves, leaf rolling and curling, yellowing of leaves, vein clearing and reduced growth such as dwarfing or stunting. These symptoms occur because viruses interfere with normal plant metabolism and development, affecting the plant's overall health and productivity.

Correct Answer: C

In 1971, the scientist T.O. Diener discovered a new type of infectious agent while studying potato spindle tuber disease. He found that the causative agent was even smaller than viruses and lacked a protein coat. This new infectious particle was called a viroid. Viroids consist only of small circular RNA molecules and are known to infect plants.

Correct Answer: A

Viroids are infectious agents that consist only of a small piece of free RNA. Unlike viruses, they do not have a protective protein coat called a capsid. Because of this simple structure, viroids are considered even smaller and simpler than viruses. They are known to infect plants and cause diseases such as potato spindle tuber disease.

Correct Answer: B

Viroids are infectious agents that consist only of a small circular RNA molecule. Unlike viruses, they do not have a protective protein coat called a capsid. Because they lack this protein coat and consist only of RNA, they are called viroids. They mainly infect plants and cause several plant diseases.

Correct Answer: B

Viroids are very small infectious agents that consist only of RNA. The RNA present in viroids is of low molecular weight and lacks a protective protein coat, which is normally present in viruses. Because of their extremely simple structure, viroids are considered even smaller and simpler than viruses and mainly infect plants.

Correct Answer: C

Prions are unique infectious agents that consist only of abnormally folded proteins. Unlike viruses and viroids, prions do not contain any nucleic acids such as DNA or RNA. These abnormal proteins can induce normal proteins in the host to fold incorrectly, leading to serious neurological diseases in animals and humans.

Correct Answer: B

Prions are infectious agents that consist only of abnormally folded proteins and do not contain DNA or RNA. They are responsible for certain neurological diseases in humans and animals. These agents are extremely small and are similar in size to viruses. Unlike viruses, however, prions lack nucleic acids and cause disease by inducing abnormal folding of normal proteins in the host.

Correct Answer: B

Prions are infectious agents made only of abnormally folded proteins. They do not contain any genetic material such as DNA or RNA. These agents are similar in size to viruses and are responsible for certain infectious neurological diseases in humans and animals. Prions cause disease by converting normal proteins in the host into abnormal forms.

Correct Answer: C

Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease in cattle, and its human counterpart Creutzfeldt–Jakob disease (CJD) are caused by prions. Prions are infectious agents made of abnormally folded proteins. Unlike viruses and bacteria, prions do not contain DNA or RNA. They cause disease by inducing normal proteins in the brain to fold abnormally, leading to severe neurological damage.

Correct Answer: A

Lichens represent a symbiotic or mutually beneficial association between algae and fungi. In this relationship, the algal partner performs photosynthesis and provides food, while the fungal partner offers protection, water and minerals. Because both organisms benefit from this association, lichens are considered an example of mutualism.

Correct Answer: A

Lichens are formed by a symbiotic association between algae and fungi. The algal partner is called the phycobiont and it is autotrophic because it performs photosynthesis and produces food. The fungal partner is called the mycobiont and it is heterotrophic, providing protection, water and minerals to the algal component.

Correct Answer: A

Lichens are a symbiotic association between algae and fungi. In this relationship, the algal component performs photosynthesis and prepares food. The fungal component provides protection, shelter and also helps absorb water and mineral nutrients from the surroundings. Because both partners benefit from this association, it is considered a mutually beneficial symbiotic relationship.

Correct Answer: B

Lichens are formed by a very close symbiotic association between an alga (phycobiont) and a fungus (mycobiont). The relationship is so intimate that both organisms grow together as a single body. Because of this close association, when we observe a lichen in nature it appears to be a single organism, even though it actually consists of two different organisms living together.

Correct Answer: B

Lichens are very sensitive to air pollution, especially pollutants like sulfur dioxide. Because they absorb water and nutrients directly from the atmosphere, polluted air can easily damage them. As a result, lichens do not grow well in polluted areas. Their presence in an environment usually indicates clean and unpolluted air.