RBSE Solutions Class 11 Biology Chapter 3 Viruses

RBSE Class 11 Biology Chapter 3 Multiple Choice Objective Questions

Question 1. Viruses are -
(a) Grandular
(b) Unicellular
(c) Multicelluar
(d) None
Answer: (b) Unicellular
In simple words: Viruses are very tiny living things, much smaller than regular cells. While not truly 'unicellular' like bacteria, they are often grouped into this category to differentiate them from larger, multicellular organisms in basic classifications, as they function as single, independent units without forming tissues.

🎯 Exam Tip: When answering about virus classification, remember their unique structure: they are not true cells but rely on host cells to multiply.

Question 2. Bacterophages are made up of -
(a) Nucleic acid
(b) Only protiens
(c) Nucleoprotein
(d) Carbohydrates
Answer: (c) Nucleoprotein
In simple words: Bacteriophages, which are viruses that infect bacteria, are basically made of two main parts: nucleic acid (their genetic material, like DNA or RNA) and a protein coat around it. When these two parts are together, we call them nucleoprotein. This combination allows them to carry genetic information and protect it.

🎯 Exam Tip: Remember that "nucleoprotein" refers to both the genetic material (nucleic acid) and its protein covering, which is key to viral structure.

Question 4. Which one is a viral disease -
(a) Typhoid
(b) TB
(c) Polio
(d) Diptheria
Answer: (c) Polio
In simple words: Polio is a sickness caused by a virus. It can harm the nervous system and make a person unable to move parts of their body. Typhoid, TB, and Diphtheria are caused by bacteria, not viruses.

🎯 Exam Tip: It is important to know which diseases are caused by viruses and which by bacteria, as this affects how they are treated or prevented.

RBSE Class 11 Biology Chapter 3 Very Short Answer Questions

Question 1. Name the virus which has single stranded DNA.
Answer: Parvoviruses are known to have single-stranded DNA as their genetic material. This is unusual for DNA viruses, as most have double-stranded DNA.
In simple words: Parvoviruses are the type of virus that carries its genetic code as one string of DNA, not a double string.

🎯 Exam Tip: Viruses can have different types of genetic material (DNA or RNA, single-stranded or double-stranded); knowing these variations is important.

Question 2. Name the virus which has double stranded RNA.
Answer: Reoviruses are a group of viruses that contain double-stranded RNA. This type of genetic material is relatively rare in the viral world. These viruses infect the digestive and respiratory systems of various organisms, including humans.
In simple words: Reoviruses are viruses that have their genetic information stored in two strands of RNA.

🎯 Exam Tip: Remember that while RNA is usually single-stranded, some viruses like reoviruses have double-stranded RNA, which is an exception.

Question 3. Write full name of TMV.
Answer: TMV stands for Tobacco Mosaic Virus. This virus is famous because it was one of the first viruses to be discovered and studied. It causes a mosaic-like pattern on the leaves of infected tobacco plants.
In simple words: TMV means Tobacco Mosaic Virus. It makes a spotted pattern on tobacco plant leaves.

🎯 Exam Tip: Full forms of common scientific abbreviations are often asked, so learn them thoroughly.

RBSE Solutions for Class 11 Biology Chapter 3 Short Answer Questions

Question 1. Virus is living or non-living, explain.
Answer: Viruses show both living and non-living characteristics, making them hard to classify. They are tiny structures, only visible under an electron microscope.
**Living properties of viruses:**
1. Viruses react to things like chemicals, heat, light, and radiation.
2. They have specific antigens that can trigger an immune response.
3. Their genetic material is either DNA or RNA, which they pass on.
4. They can only make copies of themselves inside living host cells.
5. They are able to infect host cells and are specific to which hosts they can infect.
**Non-living properties of viruses:**
1. They can be turned into crystals easily and stored indefinitely.
2. They cannot carry out their own metabolic activities.
3. They do not breathe or respire on their own.
4. They usually do not have their own enzymes for metabolic processes.
5. They do not have a cellular structure like living organisms.
In simple words: Viruses are strange because they act like living things sometimes (like making copies inside a body) and non-living things other times (like being crystals). They need living cells to be active.

🎯 Exam Tip: When explaining why viruses are difficult to classify, clearly list their living and non-living characteristics with examples for each.

Question 2. Differntiate plant and animal viruses.
Answer: Plant and animal viruses have distinct differences in their structure and how they infect hosts. Plant viruses usually infect plants, while animal viruses infect animals.
**Plant virus:**
1. **Capsid:** Often, the capsid (protein coat) is the only outer layer.
2. **Genetic material:** Mostly RNA.
3. **Nucleic acid strand:** Typically single-stranded.
4. **Nature of nucleic acid:** Usually linear.
5. **Infection:** Enters through wounds or small pores in plant cells.
**Animal virus:**
1. **Capsid:** May have an additional outer envelope besides the capsid.
2. **Genetic material:** Can be either DNA or RNA.
3. **Nucleic acid strand:** Can be single-stranded or double-stranded.
4. **Nature of nucleic acid:** Can be linear or circular.
5. **Infection:** Enters by attaching to specific cell surface receptors or through direct fusion with the host cell membrane.
In simple words: Plant viruses often have RNA and get into plants through small breaks, while animal viruses can have DNA or RNA and usually attach to specific spots on animal cells to enter.

🎯 Exam Tip: When comparing plant and animal viruses, focus on differences in genetic material (DNA vs. RNA), outer layers (capsid vs. envelope), and methods of infection.

Question 3. Explain structure of virus.
Answer: Viruses are very tiny structures that can only be seen with a powerful electron microscope. Their size usually ranges from 10 to 200 nanometers (nM), but some can be as large as 300 picometers (pM). Plant viruses tend to be smaller than animal viruses.
**Shape:** Viruses come in various shapes. Some are roughly spherical (pleiomorphic), like the Influenza virus and mumps virus. Others are icosahedral, like the Herpes virus, or helical, like the Tobacco Mosaic Virus (TMV).
**Chemical Composition:** All viruses share a basic structure. They have a central core of genetic material, which is either DNA or RNA. This core is surrounded and protected by a protein coat called a capsid. The number of nucleotide pairs in their genetic material can vary greatly, from 1,000 to 250,000, but this number is fixed for a specific type of virus. The protective protein coat is essential for the virus's survival outside a host cell.
In simple words: Viruses are very small and come in different shapes. They have a core made of DNA or RNA, which is covered by a protein layer. This simple design helps them infect other cells.

🎯 Exam Tip: Describe the virus structure by mentioning its size, shape (e.g., spherical, helical), and main components (genetic material, protein coat) to score full marks.

RBSE Solutions for Class 11 Biology Chapter 3 Essay Type Questions

Question 1. Explain nature and features of viruses.
Answer: Many ideas have been put forward about the nature of viruses, with the viral theory being the most accepted. According to this theory, viruses have unique characteristics.
1. A virus is a granular structure that cannot be seen with a regular microscope. It cannot be separated using a bacterial filter, showing how tiny it is.
2. Viruses cannot be grown in an artificial (dead) medium because they need living cells to multiply. This highlights their parasitic nature.
3. They cause specific symptoms in their host cells and react to things like temperature and humidity.
**Features of viruses:**
1. **Nature of Nucleic acid:** Viruses contain either RNA or DNA as their genetic material, but never both.
2. **Symmetry of the capsid:** The protein coat (capsid) around the genetic material can have different symmetrical arrangements, such as helical or icosahedral.
3. **Molecular weight of the virus:** Viruses have a specific molecular weight depending on their size and composition.
4. **Shape and size (Dimensions) of the viruses:** Viruses vary greatly in shape (e.g., spherical, rod-like) and size.
5. **Presence or absence of envelope:** Some viruses have an additional outer layer called an envelope, which is derived from the host cell membrane.
In simple words: Viruses are tiny particles that can't be seen with normal microscopes. They can only grow inside living things and cause specific sicknesses. They are made of either DNA or RNA with a protein coat, and can be different shapes and sizes.

🎯 Exam Tip: When discussing the nature and features of viruses, be sure to cover their microscopic size, reliance on host cells, and the basic components like nucleic acid and capsid symmetry.

Question 3. Give an account of viruses.
Answer: The word "virus" comes from the Greek word "virus," which means "venom," "poisonous fluid," or "toxin molecule."
* D.J. Ivanowsky discovered viruses in 1892 while studying mosaic disease in tobacco leaves. Later, F. Twort (1915) and F.d. Herelle (1917) separately found bacteriophages, which are viruses that infect bacteria.
* According to Luria & Dornel (1968), viruses are units where the genome is a nucleic acid. They multiply inside host cells, using the cell's machinery to create special particles called virions. These virions can then transfer the virus's genetic material to other cells.
* Matthews (1970) described a virus as consisting of one or more templates of nucleic acid (DNA or RNA) that carry hereditary characteristics. The credit for early discoveries established the foundation of virology, the study of viruses.
**Features of viruses:**
1. **Nature of Nucleic acid:** Viruses contain either RNA or DNA as their genetic material.
2. **Symmetry of the capsid:** The protein coat around the genetic material shows specific symmetry.
3. **Molecular weight of the virus:** Each virus type has a characteristic molecular weight.
4. **Shape and size (Dimensions) of the viruses:** Viruses come in various shapes and sizes.
5. **Presence or absence of envelope:** Some viruses have an outer lipid envelope.
6. **Number of chromomeres in the capsid:** Refers to the structural units within the protein coat.
7. **Diameter of coiled nucleocapsid and number of cuboid capsomeres:** Describes the arrangement and components of the virus structure.
8. **Diameter of nucleic acid coiling:** Relates to how the genetic material is packed.
9. **Intracellular multiplication:** Viruses can only multiply inside living cells.
10. **Process of virus transmission:** How viruses spread from one host to another.
In simple words: Viruses are tiny harmful particles named after "poison." Scientists discovered them by studying sick plants and bacteria. They are basically a bit of DNA or RNA wrapped in protein and can only make more copies of themselves by taking over living cells.

🎯 Exam Tip: Answering a question about viruses should include their discovery, their basic definition, and a detailed list of their key features related to genetic material, structure, and multiplication.