Exercise Chapter 5: Acellular life Class 11
MCQs with answers from Chapter 5 : Acellular Life (Federal Board, 11th Class):
MCQs – Acellular Life
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Viruses are considered nonliving because:
- A) They do not mutate.
- B) They do not locomote.
- ✅ C) They cannot reproduce independently.
- D) They have nucleic acid.
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Which of these are found in all viruses?
- A) Envelope, nucleic acid, capsid
- B) DNA, RNA, and proteins
- ✅ C) Proteins and nucleic acid.
- D) Protein, carbohydrate, lipids
-
Which step in the lytic cycle follows attachment of virus and release of DNA into the cell?
- A) Production of lysozyme
- ✅ B) Disintegration of host DNA.
- C) Assemblage
- D) DNA replication
-
Which of these is a true statement?
- A) Viruses carry with them their own ribosome for protein formation
- B) New viral ribosomes form after viral DNA enters the cell
- ✅ C) Viruses use the host ribosomes for their own ends.
- D) Viruses do not need ribosomes for protein formation
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Which part of an animal virus is not reproduced in multiple copies?
- ✅ A) Envelope.
- B) Protein
- C) Capsid
- D) Ribosome
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RNA retroviruses have a special enzyme that:
- A) Disintegrates host DNA
- B) Polymerizes host DNA
- ✅ C) Transcribes viral RNA to DNA.
- D) Translates host DNA
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Which of the following illnesses is caused by a retrovirus?
- A) Typhoid
- B) Malaria
- ✅ C) AIDS.
- D) Sleeping sickness
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The HIV primarily infects:
- A) Plasma cells
- ✅ B) Helper T cells.
- C) All white blood cells
- D) Red blood cells
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Poliomyelitis affects:
- ✅ A) Motor neuron.
- B) Sensory neuron
- C) Brain
- D) Muscles
-
HIV attaches to:
- ✅ A) CD4 protein.
- B) Nucleoprotein
- C) Lipoprotein
- D) Glycoprotein
Short Questions
1. What are the components of a bacteriophage virus?
✅ Bacteriophage structure:
- Head → Contains dsDNA enclosed in a capsid
- Tail → Hollow tube for DNA injection into the host
- Tail Fibers → Help in attachment to bacterial surface
2. What do you mean by AIDS, HIV, and TMV?
▶AIDS (Acquired Immunodeficiency Syndrome): A disease caused by HIV, leading to immune suppression
▶HIV (Human Immunodeficiency Virus): A retrovirus that infects CD4+ T-cells, weakening the immune system
▶TMV (Tobacco Mosaic Virus): A plant virus affecting tobacco plants, first discovered virus
3. Why are viruses called "obligate parasites"?
✅ Viruses lack cellular machinery and metabolism, requiring a host cell to replicate
✅ Cannot reproduce or survive independently
4. Distinguish between the lytic and lysogenic cycle of bacteriophages.
| Feature | Lytic Cycle | Lysogenic Cycle |
|---|---|---|
| Viral DNA | Replicates immediately | Integrates into host genome (prophage) |
| Host Cell Fate | Lyses (bursts) | Remains intact |
| Example | T4 phage | Lambda phage |
5. What are the uses of bacteriophages in genetic engineering?
- Vectors for gene cloning
- Gene therapy applications
- Phage display technology for protein interactions
- Phage therapy as an alternative to antibiotics
6. How are viruses classified based on their hosts?
| Type | Example |
|---|---|
| Plant Viruses | TMV (Tobacco Mosaic Virus) |
| Animal Viruses | HIV, Influenza |
| Bacteriophages | T4 Phage (infects bacteria) |
7. What are the ways to control HIV?
▷Prevention: Safe sex, no needle sharing, screening of blood transfusions
✅ Treatment: Antiretroviral Therapy (ART) – Reverse transcriptase & protease inhibitors
8. How are viruses specific?
✅ Viruses bind to specific receptors on host cells
Example:
- HIV → CD4+ T-cells
- Influenza → Respiratory cells
9. What is the difference between prions and viroids?
| Feature | Prions | Viroids |
|---|---|---|
| Composition | Protein only | RNA only |
| Disease | CJD, Mad Cow Disease | Plant diseases (Potato spindle tuber disease) |
| Resistance | Heat & UV-resistant | No protective protein coat |
10. How were viruses discovered? Give the classification of viruses.
▶ Discovery: Dmitri Iwanowsky (1892) discovered Tobacco Mosaic Virus as a filterable agent
Classification:
- Baltimore System (I–VII) (based on genetic material)
- Host-based classification (Plant, Animal, Bacteriophage)
11. Describe the structure of bacteriophage, flu virus, and HIV.
▶ Bacteriophage: Icosahedral head, tail, fibers
▶ Flu Virus: Helical RNA, envelope with spikes (Hemagglutinin, Neuraminidase)
▶ HIV: Envelope with gp120/gp41, RNA, Reverse Transcriptase enzyme
12. Discuss the parasitic nature of viruses.
✅ Viruses lack metabolism & require host machinery for replication
✅ Infect specific hosts and cause disease
✅ Cannot survive outside the host for long periods
13. How does a virus survive inside a host cell protected from the immune system?
✅ HIV & Herpes integrate into host DNA (latency)
✅ Influenza & HIV mutate rapidly to escape immunity
✅ Some viruses inhibit MHC expression, avoiding immune detection
14. Describe the life cycle of HIV. What are the treatment and control measures against AIDS?
▶ HIV Life Cycle:
1️⃣ Attachment (gp120 binds CD4 receptor)
2️⃣ Fusion & Entry
3️⃣ Reverse Transcription (RNA → DNA via Reverse Transcriptase)
4️⃣ Integration (DNA integrates into host genome)
5️⃣ Replication & Assembly
6️⃣ Budding & Maturation
✅ Treatment: Antiretroviral Therapy (ART) – Blocks reverse transcriptase, protease, and integrase
✅ Control Measures: Safe practices, blood screening, ART adherence
15. What are the social problems related to AIDS?
✅ Stigma & discrimination
✅ Loss of employment & education opportunities
✅ Mental health issues (depression, anxiety)
✅ Economic burden on healthcare systems
16. Write short notes on:
a) Hepatitis
✅ Liver inflammation caused by Hepatitis viruses (A, B, C, D, E)
✅ Hepatitis B & C can cause chronic liver disease & cancer
✅ Prevention: Vaccination (Hep A & B), safe sex, no needle sharing
b) Herpes
✅ HSV-1 (Oral herpes) – Causes cold sores
✅ HSV-2 (Genital herpes) – Sexually transmitted
✅ Latency: Can remain dormant in nerve cells & reactivate later
c) Poliomyelitis
✅ Poliovirus (Picornavirus) affects motor neurons, causing paralysis
✅ Transmission: Fecal-oral route
✅ Prevention: Salk (IPV) & Sabin (OPV) vaccines
d) Cotton Leaf Curl Disease
✅ Caused by a DNA virus transmitted by whiteflies
✅ Leads to economic losses in cotton crops (Pakistan, India)
✅ Prevention: Use of resistant plant varieties, insect control
17. Argument against the hypothesis that viruses evolved before cells.
❌ Viruses lack cellular machinery & depend on host cells
❌ Cannot evolve independently without pre-existing life
✅ Likely evolved from cellular organisms by losing metabolic functions over time
Extensive Questions
Extensive Questions with Answers
1. How were viruses discovered? Give the classification of viruses.
✅ Discovery:
- Dmitri Iwanowsky (1892) discovered the Tobacco Mosaic Virus (TMV) as a filterable agent, proving that viruses are smaller than bacteria.
- Later, Martinus Beijerinck confirmed that TMV remained infectious even after filtration, coining the term "contagium vivum fluidum" (contagious living fluid).
✅ Classification:
📌 Based on Genetic Material (Baltimore System):
| Group | Type | Example |
|---|---|---|
| I | dsDNA | Herpesvirus (HSV-1) |
| II | ssDNA | Parvoviridae |
| III | dsRNA | Rotavirus |
| IV | +ssRNA | Hepatitis C |
| V | -ssRNA | Influenza virus |
| VI | Retroviruses | HIV |
| VII | RT dsDNA | Hepatitis B (HBV) |
📌 Based on Host Specificity:
- Plant Viruses → Tobacco Mosaic Virus (TMV)
- Animal Viruses → HIV, Influenza virus
- Bacteriophages → T4 Phage
2. Describe the structure of bacteriophage, flu virus, and HIV.
✅ Bacteriophage Structure:
- Icosahedral head → Contains dsDNA inside a capsid
- Tail & Tail Fibers → Attach to bacteria and inject viral DNA
- Base Plate → Aids in bacterial cell wall penetration
✅ Flu Virus (Influenza) Structure:
- Enveloped virus with helical nucleocapsid
- Surface spikes: Hemagglutinin (HA) → Helps in host cell entry
- Neuraminidase (NA) → Helps virus exit after replication
- Genome: -ssRNA (Segmented RNA virus)
✅ HIV Structure:
- Spherical envelope with gp120 & gp41 glycoproteins
- RNA genome with Reverse Transcriptase enzyme
- Infects CD4+ T-cells, leading to immune suppression
3. Discuss the parasitic nature of viruses.
✅ Viruses are obligate intracellular parasites → Require host machinery for replication.
✅ No independent metabolism → Cannot generate ATP or synthesize proteins.
✅ Host-specificity:
- HIV → Binds CD4+ T-cells
- Influenza → Targets respiratory epithelial cells
✅ Cause host cell damage → Lytic cycle leads to cell lysis, while some viruses integrate into host genome (e.g., HIV).
4. How does a virus survive inside a host cell protected from the immune system?
✅ Immune evasion strategies:
1️⃣ Latency:
- Herpesvirus & HIV integrate into host genome and remain dormant, avoiding detection.
2️⃣ Rapid Mutation: - Influenza virus undergoes antigenic drift & shift, altering surface proteins to evade antibodies.
3️⃣ MHC Suppression: - Cytomegalovirus (CMV) reduces MHC-I expression, preventing immune recognition.
4️⃣ Cytokine Inhibition: - Some viruses block interferon (IFN) pathways, preventing antiviral responses.
5. Describe the life cycle of HIV. What are the treatment and control measures against AIDS?
✅ HIV Life Cycle:
1️⃣ Attachment → gp120 binds to CD4 receptor on T-helper cells
2️⃣ Fusion & Entry → Viral RNA enters the cell
3️⃣ Reverse Transcription → RNA → DNA via Reverse Transcriptase
4️⃣ Integration → Viral DNA integrates into host genome
5️⃣ Replication & Assembly → New viral proteins are synthesized
6️⃣ Budding & Maturation → New HIV particles exit the host cell
✅ Treatment (Antiretroviral Therapy - ART):
- Reverse Transcriptase Inhibitors (e.g., AZT)
- Protease Inhibitors (e.g., Ritonavir)
- Entry & Fusion Inhibitors
✅ Control Measures:
- Safe sex practices (condoms, PrEP)
- Blood screening before transfusions
- Early ART initiation to suppress viral load
6. Write short notes on viral diseases.
(a) Hepatitis:
✅ Liver inflammation caused by Hepatitis viruses (A, B, C, D, E)
✅ Transmission:
- Hep A & E → Fecal-oral route
- Hep B, C, D → Bloodborne & sexual transmission
✅ Prevention: Hep A & B vaccines, safe injection practices
(b) Herpes:
✅ HSV-1 (Oral herpes) → Cold sores
✅ HSV-2 (Genital herpes) → Sexually transmitted
✅ Latency in nerve cells, reactivates under stress
(c) Poliomyelitis:
✅ Poliovirus (Picornavirus) affects motor neurons, leading to paralysis
✅ Transmission: Fecal-oral route
✅ Prevention: Salk (IPV) & Sabin (OPV) vaccines
(d) Cotton Leaf Curl Disease:
✅ Caused by a DNA virus transmitted by whiteflies
✅Affects cotton crops → Economic losses in Pakistan, India
✅ Prevention: Resistant plant varieties, insect control
7. Argument against the hypothesis that viruses evolved before cells.
❌ Viruses lack cellular machinery → Cannot self-replicate without a host
❌ Dependent on host cells for energy and protein synthesis
✅ Evolved from pre-existing cellular life → Possibly originated from cellular genetic elements (e.g., plasmids, transposons)
