All Free Biology MCQs with Answers

2641. Tobacco mosaic virus was discovered by:

• A. Stanley
• B. Pasteur
• C. Lwanowsky
• D. D' Herelle

Explanation: Option C is correct. Stanley was the first scientist who crystallized tobacco mosaic virus in 1935.TMV is transmitted from infected plant to healthy plant through contact, such as by touching an infected leaf or by using the same tools on both infected and healthy plants. TMV can also be transmitted through the air, but this is less common. Lwanowsky was a Russian scientist who worked on tobacco mosaic virus. He ground diseased leaves of tobacco plants and filtered them using porcelain filter. He put this filtrate on healthy leaves and they got disease. This showed tobacco plants were not infected by bacteria but by viruses. Félix D'Hérelle was a French-Canadian microbiologist who is credited with the discovery of bacteriophages, viruses that infect bacteria. In 1917, he observed that certain bacteria cultures would clear up spontaneously, and he hypothesized that a virus was responsible for the clearing. He named the virus a bacteriophage, from the Greek words for "bacteria" and "eater." Louis Pasteur was a French chemist and microbiologist who is considered the father of microbiology. He made many important discoveries in the field of microbiology, including the germ theory of disease, pasteurization, and vaccines against rabies and anthrax.

2642. Animal viruses cannot replicate in:

• A. Blood Plasma
• B. Skin cell
• C. Plant cell
• D. All of these

Explanation: One of the most important features of viruses is that they can reproduce unity in living cells, where they reproduce by replication. Viruses cannot replicate in blood plasma. Blood plasma is the liquid part of blood that does not contain cells. It is made up of water, proteins, sugars, and other nutrients. Viruses need a host cell in order to replicate, and they cannot do so in blood plasma. Also Viruses cannot replicate in skin cells. Skin cells do not have the machinery that viruses need to replicate, such as the ribosomes that are needed to make proteins. Additionally, the skin is covered in a layer of dead cells that acts as a barrier to viruses. Viruses cannot replicate in plant cells. Viruses need to hijack the host cell's machinery in order to replicate, and plant cells have different machinery than animal cells. This is why plant viruses have evolved to specifically infect plant cells.

2643. Members of which of the following group are all parasites?

• A. Viruses
• B. Fungi
• C. Algae
• D. Bacteria

Explanation: Option A is correct.All viruses are parasites. They are obligate intracellular parasites, which means that they can only replicate inside the cells of a living host. Viruses do not have their own metabolism or ribosomes, so they need to hijack the host cell's machinery in order to reproduce. There are no fungi groups that are all parasites. Some fungi are parasitic, but others are not. Parasitic fungi are those that live on or in other organisms and derive nutrients from them. They can cause diseases in plants, animals, and humans. Not all algae are parasites. Some algae are free-living, meaning they live on their own and do not need to attach to or take nutrients from other organisms. However, there are some algae that are parasitic, meaning they attach to other organisms and derive nutrients from them.Hence, we prefer viruses to algae. Bacteria are not parasites. Parasites are organisms that live on or in other organisms and derive nutrients from them. Bacteria, on the other hand, are single-celled organisms that can live independently or in colonies. They can be found in a variety of environments, including the human body, the soil, and the water.

2644. Volume of bacteriophage is about _ of host.

• A. 1/10
• B. 1/100 times
• C. 1/100
• D. 1/1000

Explanation: Option D is correct. Viruses are very small. Size of largest virus (Poxvirus) is almost equal to size of smallest bacteria.The volume of a bacteriophage is about 1/1000th the volume of its host.

2645. Viruses cannot be grown on artificial culture media because they are:

• A. Facultative parasites
• B. Endoparasites
• C. Obligate intracellular parasites
• D. Ectoparasites

Explanation: Option C is correct. Viruses cannot be grown in anificial media because they lack metabolic machinery for the synthesis of their own nucleic acids and proteins. Facultative parasites are organisms that can live as either parasites or free-living organisms. Endoparasites are organisms that live inside the cells of their hosts. Viruses are not able to live on their own. They need to infect a host cell in order to replicate. Obligate intracellular parasites are organisms that can only live and reproduce inside the cells of a host organism. They are unable to live or reproduce on their own. Ectoparasites are organisms that live on the outside of their hosts.

2646. Virus can only survive and reproduce inside a:

• A. Animal cells
• B. Bacterial cells
• C. Living cells
• D. Non-living cells

Explanation: Option C is correct Viruses can only reproduce inside cells, but not necessarily animal cells. Some viruses can only infect plant cells, while others can infect bacterial cells. Viruses are obligate intracellular parasites ,meaning that they can only survive and reproduce inside of a living cell. They are not considered to be living organisms because they do not have all the characteristics of living things, such as the ability to reproduce on their own. Viruses cannot survive and reproduce inside non-living cells. Viruses are not alive, and they need a living cell to replicate. When a virus infects a cell, it injects its genetic material into the cell. The cell's machinery then uses the genetic material to produce new copies of the virus. These new copies of the virus can then infect other cells, and the cycle continues.

2647. Which one of the following is double stranded virus?

• A. Poxvirus
• B. Parvovirus
• C. Reovirus
• D. Togavirus

Explanation: Option A is correct.Pox viruses are a family of viruses that contain double-stranded DNA. This means that their genetic material is made up of two strands of DNA that are linked together.The parvovirus strand that causes parvoviral disease in dogs is called Canine parvovirus (CPV). It is a single-stranded DNA virus that is very stable and can survive for long periods of time in the environment. CPV is highly contagious and can be spread through contact with infected dogs, their saliva, feces, or vomit.Reoviruses are a family of double-stranded RNA (dsRNA) viruses that infect a wide range of hosts, including humans, animals, and plants. They are named for respiratory enteric orphan viruses, as they were originally discovered in respiratory and enteric (intestinal) secretions of humans and animals. Reoviruses are non-enveloped, meaning that they do not have a lipid membrane surrounding their capsid. The strand of a toga virus is positive-sense, single-stranded RNA. This means that the RNA is complementary to the mRNA that is used to produce proteins. The positive-sense RNA is also infectious, which means that it can be used to infect cells directly. Viruses are classified on different basis such as capsid shape, types of hosts and genome. On basis of genome there are many categories of viruses such as:• Double stranded DNA viruses:Herpesvirus, papillomavirus, poxvirus• Single stranded DNA viruses:Parvovirus, circovirus • Double stranded RNA viruses:Reovirus, rotavirus • Single stranded viruses:Poliovirus, coronavirus,Influenza virus, HIV,

2648. Which of the following is not essential part of virus?

• A. Nucleic acid
• B. Capsid
• C. Envelope
• D. None of these

Explanation: Not all viruses have envelope ,but a virus should have a nucleic acid and a protein coat always. Not all viruses have envelope ,but a virus should have a nucleic acid and a protein coat always. The complete, mature and infectious particle is known as virion. The virions are composed of a central core of nucleic acid, either DNA or RNA, which is also known as the genome and is surrounded by a protein coat, the capsid.In some animal viruses the nucleocapsid (nucleic acid and capsid) is covered by another membrane derived from the host cell, the envelope. Non enveloped viruses are known as naked virions.ntral core of nucleic acid, either DNA or RNA, which is also known as the genome and is surrounded by a protein coat, the capsid.In some animal viruses the nucleocapsid (nucleic acid and capsid) is covered by another membrane derived from the host cell, the envelope. Non enveloped viruses are known as naked virions.

2649. The genome of most of the animal viruses contain:

• A. DNA
• B. Protein
• C. RNA
• D. Both DNA and RNA

Explanation: Genome of animal viruses mostly contains DNA, whereas genome of plant viruses mostly contain RNA. So, option A is correct.

2650. Among followings, _ enzyme is naturally found in HIV.

• A. DNA polymerase
• B. Reverse transcriptase
• C. RNA polymerase
• D. Ligase

Explanation: Among the options provided, "Reverse transcriptase" is the enzyme naturally found in HIV.Here's an explanation of each option:1. DNA polymerase: DNA polymerase is an enzyme that plays a crucial role in DNA replication and repair. It is not naturally found in HIV.2. Reverse transcriptase: Reverse transcriptase is an enzyme that is naturally found in HIV. It is responsible for the conversion of the virus's RNA genome into DNA, which can then be integrated into the host cell's genome. This process is a critical step in the HIV replication cycle.3. RNA polymerase: RNA polymerase is an enzyme responsible for transcribing DNA into RNA during gene expression. It is not naturally found in HIV.4. Ligase: Ligase is an enzyme involved in the repair and joining of DNA strands. It is not naturally found in HIV.So, among these options, only "Reverse transcriptase" is the enzyme naturally found in HIV, and it is a key player in the virus's life cycle.