How is HIV transmitted from person to person?

HIV is transmitted through unprotected sexual contact, blood transfusion or sharing needles, and mother-to-child during pregnancy, delivery, or breastfeeding. HIV is NOT transmitted by mosquito bites, handshakes, hugs, or sharing food.

A provirus is HIV viral DNA that has been integrated into the host cell's genome by the enzyme integrase. It replicates with the host chromosome and can remain latent for years.

What test is used to detect HIV?

ELISA is the standard screening test for HIV antibodies. Western blot confirms a positive ELISA. The p24 antigen test can detect infection earlier.

Are prions and viroids the same as viruses?

No. Prions are infectious misfolded proteins with no nucleic acid. Viroids are circular single-stranded RNA molecules with no protein coat that infect only plants. Viruses always contain a protein capsid.

Do viruses die from AIDS or the virus itself?

AIDS patients typically die from secondary opportunistic infections (like Pneumocystis pneumonia, TB) or malignancies (Kaposi's sarcoma), not from HIV itself.

Biodiversity MDCAT Notes, MCQs, Past Papers & Answers – Viruses & AIDS

Q: What is biodiversity in simple words?

Biodiversity is the variety of all living things on Earth — plants, animals, microorganisms, and the ecosystems they form. In MDCAT Biology, this chapter covers virus classification and the viral disease AIDS.

Q: What is a virus in biology?

A virus is a tiny infectious agent made of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. Viruses are obligate intracellular parasites — they cannot reproduce without a host cell.

Q: How many types of viruses are there?

In MDCAT Biology, viruses are grouped in five ways: by symmetry (helical, icosahedral, complex, brick-shaped, bullet-shaped), by nucleic acid (dsDNA, ssDNA, dsRNA, ssRNA+ , ssRNA−), by host (bacteria, plants, animals), by envelope (enveloped vs naked), and by disease caused.

Q: What is the difference between DNA and RNA viruses?

DNA viruses (Adenovirus, Herpes, Pox, HBV) have DNA genomes and typically replicate in the nucleus. RNA viruses (HIV, Influenza, Polio, Rabies, TMV) have RNA genomes and usually replicate in the cytoplasm. A virus contains either DNA or RNA, never both.

Q: What does HIV stand for?

HIV stands for Human Immunodeficiency Virus. It is a retrovirus with single-stranded RNA that attacks CD4+ helper T-cells and macrophages, leading to severe immunodeficiency and eventually AIDS.

Q: What does AIDS stand for?

AIDS stands for Acquired Immune Deficiency Syndrome. It is the final stage of HIV infection when CD4+ T-cell count drops below 200 cells/mm³.

Q: What is the window period in HIV?

The window period is the time right after HIV infection when the virus is present in the blood but antibodies are not yet detectable by standard tests (typically 2-4 weeks). The person is infectious during this period.

Q: Which virus causes AIDS?

AIDS is caused by HIV (Human Immunodeficiency Virus), a retrovirus. HIV progressively destroys CD4+ T-helper cells, weakening the immune system.

🧬 Chapter 1 · MDCAT Biology

📅 Updated Jan 2026 ⏱️ 25 min read 🎯 High-yield

Biodiversity — Viruses & AIDS (Complete MDCAT Notes)

Full MDCAT Biology Chapter 1 on virus classification and HIV/AIDS. Includes 5 classification tables, HIV structure, transmission, symptoms, life cycle, plus 169 solved MCQs with explanations and year-wise past papers.

⚡Quick Answers to Common Searches

Direct, snippet-optimized answers to the top questions students search about Biodiversity, viruses, and HIV/AIDS.

What is biodiversity?

Biodiversity is the variety of all living things on Earth — plants, animals, microorganisms, and the ecosystems they form. In MDCAT Chapter 1, it specifically covers virus classification and AIDS.

What is a virus?

A virus is an infectious agent made of DNA or RNA enclosed in a protein coat called a capsid. Viruses are obligate intracellular parasites — they cannot reproduce outside a host cell.

How many types of viruses are there?

In MDCAT, viruses are grouped in 5 ways: by symmetry, by nucleic acid, by host, by envelope, and by disease caused.

Do viruses have DNA or RNA?

A virus contains either DNA or RNA — never both. HIV has ssRNA, Adenovirus has dsDNA, Parvovirus has ssDNA.

What is the shape of TMV?

TMV (Tobacco Mosaic Virus) has helical (rod-shaped) symmetry with ssRNA. Discovered by Dmitri Iwanowsky in 1892.

What is the shape of a bacteriophage?

Bacteriophages have complex (binal) symmetry: an icosahedral head containing DNA plus a helical tail for injection.

What is a capsid?

A capsid is the protein shell protecting viral genetic material, made of repeating subunits called capsomeres.

What does HIV stand for?

HIV = Human Immunodeficiency Virus. A retrovirus with ssRNA that attacks CD4+ helper T-cells.

What does AIDS stand for?

AIDS = Acquired Immune Deficiency Syndrome. Final stage of HIV when CD4+ count drops below 200 cells/mm³.

How is HIV transmitted?

Through unprotected sex, blood transfusion/shared needles, and mother-to-child. NOT by mosquito bites, hugs, or food sharing.

What is the window period in HIV?

The window period is when virus is present but antibodies not yet detectable (2–4 weeks). Person is infectious during this period.

What is a provirus?

A provirus is HIV DNA integrated into the host genome by integrase. It replicates with the host and can stay latent for years.

What does reverse transcriptase do?

Reverse transcriptase converts HIV's ssRNA into DNA. It lacks proofreading — giving HIV its high mutation rate.

Virus vs bacteria?

Viruses are 20–300 nm, acellular, no metabolism, cannot reproduce alone. Bacteria are 1–5 µm, living cells, own metabolism.

How many MCQs from Biodiversity?

Biodiversity typically contributes 4–6 MCQs out of 81 Biology MCQs in MDCAT.

❓People Also Ask — Biodiversity & HIV/AIDS

Questions students most frequently search about this chapter. Answers are direct and exam-focused.

QWhat is the difference between DNA and RNA viruses?

DNA viruses (Adenovirus, Herpes, Pox, HBV) contain DNA and typically replicate in the nucleus. RNA viruses (HIV, Influenza, Polio, Rabies, TMV) contain RNA and usually replicate in the cytoplasm. No virus contains both DNA and RNA.

QWhat are the first symptoms of HIV?

The first symptoms appear 2–4 weeks after infection as acute retroviral syndrome — fever, sore throat, rash, swollen lymph nodes, muscle aches, and fatigue. Many mistake these for flu.

QHow long can a person live with HIV without treatment?

Without treatment, HIV typically progresses to AIDS in 8–10 years. With modern antiretroviral therapy (ART), people with HIV can live a normal lifespan.

QWhat are the 4 stages of HIV?

(1) Acute HIV infection — flu-like symptoms 2–4 weeks after infection. (2) Clinical latency — asymptomatic but virus present. (3) Symptomatic HIV — CD4 200–500. (4) AIDS — CD4 below 200, severe opportunistic infections.

QWhich test is used to detect HIV?

ELISA is the screening test. Western blot confirms a positive ELISA. The p24 antigen test detects infection earlier, during the window period.

QWhat is the difference between lytic and lysogenic cycle?

Lytic cycle: virus immediately replicates and destroys the host to release new virions. Lysogenic cycle: viral DNA integrates as a prophage and replicates passively.

QWhat is the function of gp120 and gp41 in HIV?

gp120 binds CD4 receptors on helper T-cells. gp41 mediates fusion between viral envelope and host membrane.

QWhich virus causes smallpox?

Variola virus (a poxvirus) caused smallpox. Eradicated globally in 1980.

QWhat are prions and viroids?

Prions are infectious misfolded proteins with no nucleic acid. Viroids are circular ssRNA molecules with no protein coat that infect only plants.

QHow does HIV damage the immune system?

HIV infects and destroys CD4+ helper T-cells — the "commanders" of the immune system. Without them, B-cells and cytotoxic T-cells cannot respond effectively.

QWhat are opportunistic infections in AIDS?

Pneumocystis jirovecii pneumonia (most common), tuberculosis, Kaposi's sarcoma, Candida infections, and cryptococcal meningitis.

QIs there a cure for HIV or AIDS?

As of 2026, there is no cure for HIV, but antiretroviral therapy (ART) can suppress the virus to undetectable levels, allowing near-normal lifespan.

QDifference between naked and enveloped viruses?

Enveloped viruses (HIV, Influenza, Herpes, Rabies) have a lipid envelope from host membrane. Naked viruses (Adenovirus, Polio, TMV) lack it and are more stable.

QWhich MDCAT Biology chapter is Biodiversity?

Biodiversity is Chapter 1 in the MDCAT Biology syllabus (PMDC/PMC).

QWhat are the most important MDCAT topics from Biodiversity?

HIV structure (gp120, gp41, p24), transmission (NOT mosquitoes), window period, provirus, reverse transcriptase, TMV shape, bacteriophage structure, viral nucleic acid rules, lysogenic vs lytic cycles.

QHow many capsomeres does Adenovirus have?

Adenovirus has 252 capsomeres (240 hexons + 12 pentons). Herpesvirus has 162 capsomeres (150 hexons + 12 pentons).

QWho discovered the first virus?

Dmitri Iwanowsky (1892) first showed the agent could pass through a porcelain filter. Wendell Stanley (1935) crystallized TMV.

QWhat diseases do viruses cause?

AIDS (HIV), Smallpox (Variola), Polio (Poliovirus), Rabies, Hepatitis B, Mumps & Measles, Chickenpox, Common cold (Rhinovirus).

QCan viruses be crystallized?

Yes. Wendell Stanley crystallized TMV in 1935, proving viruses can form crystals outside a host — a property of non-living matter.

QWhat is the size of a typical virus?

Viruses are 20–300 nanometers (nm). Poliovirus is one of the smallest (~20 nm); Poxviruses are among the largest (~300 nm).

📋Syllabus & Learning Outcomes

According to PMDC/PMC MDCAT syllabus, Biodiversity covers:

1.1 Classify viruses on the basis of their structure / number of strands / diseases / hosts etc.
1.2 Identify symptoms, mode of transmission and cause of viral disease (AIDS).

📝Full Notes — Virus Classification & HIV/AIDS

1.1 Classification of Viruses

A. By Structure / Symmetry

Type	Shape	Examples
Helical	Rod-shaped	TMV, Influenza
Icosahedral	Spherical (20 faces)	Adenovirus, Polio, Herpes
Complex / Binal	Head + Tail	Bacteriophage (T4)
Brick-shaped	Complex	Pox virus (smallpox)
Bullet-shaped	Bullet	Rabies virus

B. By Nucleic Acid (Strands)

Genome	Examples
dsDNA	Adenovirus, Herpesvirus, Poxvirus
ssDNA	Parvovirus
dsRNA	Reovirus (Rotavirus)
ssRNA (+ sense)	Polio, TMV, HIV (retrovirus)
ssRNA (− sense)	Influenza, Rabies

Golden rule: A virus contains either DNA or RNA, never both.

C. By Host

Bacteriophages – infect bacteria (T4, lambda phage). Not animal viruses!
Phytophagineae – plant viruses, mostly ssRNA (TMV, potato virus).
Zoophagineae – animal viruses (HIV, Rabies, Influenza, Polio).

D. By Envelope

Enveloped	Naked (Non-enveloped)
HIV, Influenza, Herpes, Rabies	Adenovirus, Polio, TMV

Trap: Envelope is taken from host membrane during budding. Naked viruses are more resistant to heat & detergents.

E. By Disease

AIDS → HIV
Smallpox → Variola virus
Polio → Poliovirus
Rabies → Rabies virus
Hepatitis B → HBV (DNA virus)
Mumps & Measles → Paramyxoviruses
Chickenpox/Shingles → Varicella-zoster
Common cold → Rhinovirus

1.2 AIDS — Cause, Transmission & Symptoms

Causative Agent

HIV (Human Immunodeficiency Virus) – retrovirus, ssRNA, enveloped.

2 copies of RNA + enzymes: reverse transcriptase, integrase, protease.
Envelope spikes: gp120 (attachment to CD4) & gp41 (fusion).
Capsid: conical, made of p24 protein.
Target cells: CD4+ T-helper cells, macrophages.

Modes of Transmission

✅ Blood transfusion / contaminated needles.
✅ Unprotected sexual contact.
✅ Mother to child (pregnancy, delivery, breastfeeding).
❌ NOT by: mosquito bites, handshake, food sharing, coughing.

MCQ favourite: "Which is NOT a mode of HIV transmission?" → Mosquito bites.

Symptoms & Stages

Acute HIV – flu-like (fever, rash, sore throat) – often missed.
Clinical latency – no symptoms, but virus present → Window period.
AIDS – CD4 count < 200 cells/mm³. Opportunistic infections: Pneumocystis jirovecii pneumonia, TB, Kaposi's sarcoma.

Trap: AIDS patients die from secondary infections, not HIV itself.

Diagnosis

1st – ELISA (screening).
Confirm – Western blot.
Early – p24 antigen test.

HIV Life Cycle

gp120 binds CD4 receptor → entry
Reverse transcriptase: RNA → DNA
Integrase: viral DNA integrates → provirus
New virions bud out (cell survives)

Trap: HIV uses budding, not lysis to exit the cell.

High-Yield Points & Common Traps

Structure: TMV = helical, Adenovirus = icosahedral, Bacteriophage = complex.
Nucleic acid: Virus has only one type. HIV = ssRNA, Adenovirus = dsDNA.
Host: Bacteriophage infects bacteria, not humans.
Envelope: HIV, Influenza are enveloped; Adenovirus & Polio are naked.
AIDS cause: HIV – retrovirus (RNA → DNA).
HIV attachment: gp120 to CD4 receptor.
Window period: virus present, antibodies absent.
AIDS marker: Pneumocystis jirovecii pneumonia.
Provirus: integrated HIV DNA in host.
Reverse transcriptase: RNA-dependent DNA polymerase.

✅Practice MCQs — Test 1

🧪 Basic Concepts

50 MCQs

1Which of the following scientists first discovered that the agent causing tobacco mosaic disease could pass through a porcelain filter?

A. Martinus Beijerinck
B. Wendell Stanley
C. Dmitri Iwanowsky
D. Louis Pasteur

Answer: C. Dmitri Iwanowsky

Dmitri Iwanowsky (1892) first showed the infectious agent could pass through a porcelain filter, later called a virus.

2Viruses are considered 'obligate intracellular parasites' because:

A. They can be crystallized
B. They lack their own metabolic machinery
C. They possess a cell wall
D. They are composed of only DNA

Answer: B

Viruses lack ribosomes and enzymes for metabolism, so they must hijack host cells to replicate.

3The protein coat of a virus that encloses the genetic material is known as the:

A. Capsid
B. Envelope
C. Nucleoid
D. Capsomere

Answer: A. Capsid

The capsid is the protein shell that protects the viral genome.

4How many capsomeres are present in the capsid of an Adenovirus?

A. 20
B. 252
C. 162
D. 60

Answer: B. 252

Adenovirus has 252 capsomeres (240 hexons + 12 pentons).

5Viruses that consist of a core of nucleic acid surrounded by a protein coat but lack an outer lipid layer are called:

A. Naked viruses
B. Virinos
C. Prions
D. Enveloped viruses

Answer: A. Naked viruses

Naked viruses lack an envelope; they are more resistant to environmental stress.

6According to classification based on host, which virus specifically infects bacteria?

A. Cyanophages
B. Phagineae
C. Zoophagineae
D. Phytophagineae

Answer: B. Phagineae

Bacteriophages are viruses that infect bacteria; 'Phagineae' is a historical term.

7Which of the following is an example of a double-stranded RNA virus?

A. Influenza virus
B. Reovirus
C. Pox virus
D. HIV

Answer: B. Reovirus

Reoviridae (e.g., Rotavirus) have double-stranded RNA genomes.

8Bacteriophages usually exhibit which type of symmetry?

A. Asymmetrical
B. Binal (Tadpole-like)
C. Helical
D. Spherical

Answer: B. Binal (Tadpole-like)

Most bacteriophages have binal symmetry: icosahedral head + helical tail.

9The viral envelope is typically derived from:

A. Bacterial cell wall
B. De novo synthesis
C. Viral proteins
D. Host cell membrane

Answer: D. Host cell membrane

Enveloped viruses acquire their lipid envelope from host cell membranes during budding.

10Which virus is responsible for causing Smallpox?

A. Variola virus
B. Rhinovirus
C. Varicella zoster
D. Mumps virus

Answer: A. Variola virus

Variola virus (a poxvirus) caused smallpox, eradicated by 1980.

11Retroviruses are unique because they possess which enzyme?

A. DNA Polymerase
B. Lysozyme
C. Reverse Transcriptase
D. RNA Replicase

Answer: C. Reverse Transcriptase

Reverse transcriptase converts viral RNA into DNA, integrating into the host genome.

12HIV primarily targets which type of cells?

A. Helper T-lymphocytes (CD4+)
B. B-lymphocytes
C. Cytotoxic T-cells
D. Red blood cells

Answer: A. Helper T-lymphocytes

HIV binds CD4 receptors on helper T cells, leading to their destruction.

13Which of the following is NOT a mode of transmission for HIV?

A. Blood transfusion
B. Sexual contact
C. Breastfeeding
D. Mosquito bites

Answer: D. Mosquito bites

HIV is not transmitted by mosquitoes; it requires direct blood/body fluid exchange.

14The protein spikes on the HIV envelope that facilitate attachment are:

A. gp41
B. Integrase
C. p24
D. gp120

Answer: D. gp120

gp120 binds CD4 receptor; gp41 then mediates fusion.

15During the life cycle of HIV, viral DNA is integrated to form a:

A. Capsid
B. Provirus
C. Prophage
D. Plasmid

Answer: B. Provirus

Integrated HIV DNA is called a provirus; it remains latent until activated.

16Which stage of HIV is characterized by severe opportunistic infections like pneumonia?

A. Window period
B. AIDS
C. Acute infection
D. Asymptomatic period

Answer: B. AIDS

AIDS is the final stage with CD4 count <200 and opportunistic infections.

17Hepatitis B virus is classified as a:

A. Single-stranded DNA virus
B. Double-stranded DNA virus
C. Double-stranded RNA virus
D. Single-stranded RNA virus

Answer: B

HBV has a partially double-stranded DNA genome and uses reverse transcription.

18The time period during which blood tests negative for HIV antibodies but is still infectious:

A. Incubation period
B. Latent period
C. Window period
D. Lytic cycle

Answer: C. Window period

Window period: before seroconversion, antibodies undetectable but virus present.

19Which virus causes 'hydrophobia' as a symptom in humans?

A. Rabies virus
B. Influenza virus
C. Polio virus
D. Mumps virus

Answer: A. Rabies virus

Hydrophobia (fear of water) is a classic sign of rabies.

20Prions are infectious particles composed of:

A. DNA only
B. RNA only
C. RNA and Proteins
D. Proteins only

Answer: D. Proteins only

Prions are misfolded proteins (no nucleic acid) that cause spongiform encephalopathies.

21The viral enzyme that cuts the viral polyprotein into functional units is:

A. Protease
B. Integrase
C. Polymerase
D. Ligase

Answer: A. Protease

Viral protease cleaves polyproteins into individual functional proteins.

22A virus in a dormant state within a host cell without causing lysis is in which cycle?

A. Lysogenic cycle
B. Lytic cycle
C. Cell cycle
D. Krebs cycle

Answer: A. Lysogenic cycle

Lysogenic: viral DNA integrates and replicates with host without lysis.

23Poliomyelitis is primarily a disease of the:

A. Digestive system
B. Respiratory system
C. Circulatory system
D. Nervous system

Answer: D. Nervous system

Polio virus infects motor neurons, causing paralysis.

24The total number of capsomeres in a Herpes virus is:

A. 162
B. 252
C. 12
D. 20

Answer: A. 162

Herpesvirus capsid contains 162 capsomeres (150 hexons + 12 pentons).

25Viroids differ from viruses in that they lack:

A. Infectiousness
B. Nucleic acids
C. Protein coat
D. Ability to replicate

Answer: C. Protein coat

Viroids are circular RNA molecules with no protein coat.

26What is the shape of the Tobacco Mosaic Virus (TMV)?

A. Helical (Rod-shaped)
B. Bullet-shaped
C. Icosahedral
D. Tadpole-shaped

Answer: A. Helical

TMV is a helical rod-shaped virus.

27Which component of HIV causes its high mutation rate?

A. Host Cell Enzymes
B. Stable Capsid
C. Lipid Envelope
D. Inaccurate Reverse Transcriptase

Answer: D

Reverse transcriptase lacks proofreading, leading to high mutation rate.

28The major cell-surface receptor for HIV entry into macrophages is:

A. CD4
B. CD8
C. Insulin receptor
D. Hemagglutinin

Answer: A. CD4

HIV uses CD4 as primary receptor; macrophages also express CD4.

29Smallpox was officially declared eradicated by the WHO in what year?

A. 1950
B. 2000
C. 1980
D. 1918

Answer: C. 1980

Smallpox eradication was certified in 1980 after global vaccination campaigns.

30Influenza virus belongs to which group of viruses?

A. Naked DNA viruses
B. Naked RNA viruses
C. Enveloped DNA viruses
D. Enveloped RNA viruses

Answer: D

Influenza is enveloped with a segmented ssRNA genome.

31Which of these is a symptom of the 'asymptomatic carrier' stage of HIV?

A. Persistent cough
B. Rapid weight loss
C. No visible symptoms
D. Skin lesions

Answer: C

Asymptomatic carriers have no symptoms but can transmit HIV.

32Which bacteriophage follows both lytic and lysogenic cycles and is used in research?

A. T4 phage
B. TMV
C. Lambda phage
D. HIV

Answer: C. Lambda phage

Lambda phage is a temperate phage used extensively in molecular biology.

33The size of a virus is typically measured in:

A. Micrometers
B. Nanometers
C. Millimeters
D. Centimeters

Answer: B. Nanometers

Viruses range from 20-300 nm, measured in nanometers.

34Which describes the 'Lytic' cycle?

A. The virus helps the host divide faster
B. The virus remains dormant
C. Host cell used as factory and then destroyed
D. Viral DNA integrates with host DNA

Answer: C

Lytic cycle ends with host cell lysis and release of new virions.

35HIV was first isolated and identified in the year:

A. 1990
B. 1955
C. 1970
D. 1984

Answer: D. 1984

HIV was isolated in 1983-1984 by Luc Montagnier and Robert Gallo.

36Which virus causes Mumps and Measles?

A. Paramyxoviruses
B. Arboviruses
C. Picornaviruses
D. Pox viruses

Answer: A. Paramyxoviruses

Both mumps and measles are caused by paramyxoviruses.

37The most common opportunistic infection in AIDS patients is pneumonia caused by:

A. Influenza virus
B. Streptococcus pneumoniae
C. Pneumocystis jirovecii
D. Mycobacterium tuberculosis

Answer: C

Pneumocystis jirovecii pneumonia (PCP) is a common AIDS-defining illness.

38Vertical transmission of HIV refers to:

A. Transmission from mother to offspring
B. Transmission through physical contact
C. Transmission through contaminated needles
D. Transmission through insect vectors

Answer: A

Vertical: mother-to-child during pregnancy, birth, or breastfeeding.

39Which of the following is a viral disease characterized by inflammation of liver?

A. Hepatitis
B. Meningitis
C. Nephritis
D. Gastritis

Answer: A. Hepatitis

Hepatitis viruses (A, B, C, D, E) cause liver inflammation.

40A fully formed, infectious viral particle outside a host cell is called a:

A. Virion
B. Provirus
C. Prion
D. Viroid

Answer: A. Virion

A virion is the complete, infectious viral particle.

41In the bacteriophage, the 'tail' is used for:

A. Storing genetic material
B. Protection from heat
C. Attachment and injection
D. Energy production

Answer: C

The tail helps attach to bacteria and injects viral DNA.

42Reverse Transcriptase is also known as:

A. RNA-dependent RNA polymerase
B. DNA-dependent RNA polymerase
C. RNA-dependent DNA polymerase
D. DNA-dependent DNA polymerase

Answer: C

Reverse transcriptase synthesizes DNA from RNA template.

43Which of the following is true regarding viral genomes?

A. They always contain both DNA and RNA
B. They contain either DNA or RNA
C. They contain only single-stranded DNA
D. They contain only circular genomes

Answer: B

Viruses have either DNA or RNA, never both.

44Kaposi's sarcoma is a type of cancer affecting which tissue in AIDS patients?

A. Bone marrow
B. Brain tissue
C. Epithelial lining of gut
D. Blood vessels

Answer: D. Blood vessels

Kaposi's sarcoma arises from endothelial cells, associated with HHV-8.

45The conversion of a lysogenic bacterium to a lytic one is called:

A. Induction
B. Conjugation
C. Transformation
D. Transduction

Answer: A. Induction

Induction (e.g., UV light) triggers prophage to enter lytic cycle.

46Which is NOT a characteristic of life exhibited by viruses?

A. Independent Metabolism
B. Heredity
C. Mutation
D. Reproduction

Answer: A

Viruses lack metabolism; they rely entirely on host cells.

47Shingles is a recurring form of which viral infection?

A. Chickenpox
B. Mumps
C. Hepatitis
D. Measles

Answer: A. Chickenpox

Shingles results from reactivation of varicella-zoster virus.

48Which of the following is used as a screening test for HIV?

A. ELISA
B. PCR
C. Biopsy
D. Western Blot

Answer: A. ELISA

ELISA is the primary screening test; Western blot confirms.

49T-even phages are:

A. Plant viruses
B. DNA viruses
C. RNA viruses
D. Spherical viruses

Answer: B. DNA viruses

T-even phages (T2, T4, T6) are DNA bacteriophages.

50The incubation period for HIV can range from:

A. 48 to 72 hours
B. Several months to 10 years or more
C. A few days to weeks
D. Exactly one year

Answer: B

HIV incubation can be years (average 8-10 years) without treatment.

✅Practice MCQs — Test 2

🧪 Advanced Concepts

25 MCQs

1Which describes the genome of TMV more specifically?

A. Single-stranded, positive-sense RNA
B. Circular double-stranded DNA
C. Single-stranded DNA
D. Double-stranded RNA

Answer: A

TMV has ssRNA genome that acts directly as mRNA (positive-sense).

2In the T4 bacteriophage, the function of 'pins' at the base plate:

A. Contract the tail sheath
B. Store the DNA
C. Synthesize lysozyme
D. Firmly anchor the virus to the host cell wall

Answer: D

Pins attach irreversibly to the bacterial cell wall before DNA injection.

3Which viral group is characterized by 'bullet-shaped' morphology?

A. Poxviruses
B. Rhabdoviruses
C. Retroviruses
D. Bacteriophages

Answer: B. Rhabdoviruses

Rhabdoviruses (e.g., rabies) have a distinctive bullet-like shape.

4The term 'prophage' specifically refers to:

A. A virus that lost its envelope
B. The protein shell of a phage
C. Viral DNA integrated into bacterial chromosome
D. An immature viral particle

Answer: C

A prophage is phage DNA integrated into the host bacterial genome.

5Which enzyme is NOT carried inside the HIV virion?

A. Reverse Transcriptase
B. Integrase
C. RNA Polymerase II
D. Protease

Answer: C

RNA Polymerase II is a host enzyme; HIV carries RT, integrase, and protease.

6The HIV protein gp41 is primarily involved in:

A. Fusion of viral envelope with host membrane
B. Binding to CD4 receptor
C. Protecting RNA genome
D. Cleaving polyprotein

Answer: A

gp41 mediates membrane fusion after gp120 binds CD4.

7Hepatitis C is most commonly transmitted through:

A. Inhalation of respiratory droplets
B. Contaminated water
C. Contaminated blood and needles
D. Fecal-oral route

Answer: C

HCV is blood-borne; sharing needles and unscreened blood are primary routes.

8Which host component does HIV use to synthesize its proteins?

A. Ribosomes
B. Mitochondria
C. Lysosomes
D. Golgi apparatus

Answer: A. Ribosomes

All viruses rely on host ribosomes to translate their viral mRNA.

9A person who is 'HIV positive' but no symptoms of AIDS is usually in which stage?

A. Clinical latency (Asymptomatic)
B. Incubation period
C. Acute retroviral syndrome
D. Secondary infection stage

Answer: A

During clinical latency, HIV replicates at low levels and the person is asymptomatic.

10The DNA of Poxvirus is uniquely situated because it:

A. Is linear and segmented
B. Replicates in the host cytoplasm
C. Is single-stranded
D. Lacks a protein capsid

Answer: B

Poxviruses replicate in the cytoplasm, unlike most DNA viruses.

11Which is a primary characteristic of Viroids?

A. They consist of circular ssRNA
B. They are larger than most viruses
C. They contain reverse transcriptase
D. They primarily infect animals

Answer: A

Viroids are naked, circular ssRNA molecules that infect plants.

12The 'window period' in HIV is primarily due to:

A. Time for body to produce detectable antibodies
B. Low viral replication
C. Virus hiding in bone marrow
D. Integration into host genome

Answer: A

It takes weeks for antibody levels to become detectable.

13Which of the following viruses is 'naked' (lacks an envelope)?

A. Herpes virus
B. Influenza virus
C. Polio virus
D. HIV

Answer: C. Polio virus

Polio is non-enveloped icosahedral; others are enveloped.

14In HIV, the p24 protein is the major component of the:

A. Genome
B. Matrix
C. Envelope
D. Capsid

Answer: D. Capsid

p24 forms the conical capsid enclosing HIV RNA genome.

15During the lysogenic cycle, the prophage DNA replicates:

A. Only when exposed to UV light
B. Independently of bacterial chromosome
C. Along with host chromosome during division
D. By hijacking host Golgi body

Answer: C

The prophage replicates passively with the bacterial chromosome.

16Which is a classic symptom of the 'Prodromal' phase of viral infection?

A. Vague symptoms like fatigue and mild fever
B. Complete recovery
C. Organ failure
D. Specific rashes

Answer: A

Prodrome is the early stage with non-specific symptoms.

17The term 'Temperate Phage' is most closely associated with:

A. High temperature environments
B. The Lysogenic cycle
C. Immediate host cell death
D. RNA-based genomes

Answer: B

Temperate phages can enter lysogenic cycle instead of killing host.

18What is the polarity of the first DNA strand made by reverse transcriptase?

A. Triple-stranded
B. Antisense (Complementary)
C. Identical to RNA
D. Positive sense

Answer: B

The first DNA strand (cDNA) is complementary (antisense) to RNA.

19Which of the following is NOT a characteristic of Prions?

A. Cause neurodegenerative diseases
B. Contain a small amount of DNA
C. Resistant to heat and chemicals
D. Involve misfolding of normal proteins

Answer: B

Prions contain no nucleic acid; they are solely misfolded proteins.

20The bacteriophage T4 tail sheath contracts to:

A. Produce viral proteins
B. Absorb nutrients
C. Drive the core tube through bacterial cell wall
D. Break down viral capsid

Answer: C

Contraction pushes hollow core through bacterial envelope.

21Which Hepatitis virus requires Hepatitis B to replicate?

A. Hepatitis E
B. Hepatitis D (Delta agent)
C. Hepatitis A
D. Hepatitis C

Answer: B. Hepatitis D

HDV is defective and requires HBsAg of HBV for packaging.

22The polyhedral head of a bacteriophage contains:

A. Host cell lipids
B. The viral genome
C. Ribosomes
D. Enzymes for energy production

Answer: B. The viral genome

The head houses the phage's nucleic acid.

23What is the primary reason HIV cannot be easily cured?

A. It only infects red blood cells
B. Integration of provirus into host genome
C. Virus too large to filter
D. Lacks a protein coat

Answer: B

HIV integrates DNA into host chromosomes; latent provirus evades therapy.

24Influenza pandemics are often caused by 'Antigenic Shift' which refers to:

A. Loss of viral envelope
B. Reassortment of genomic segments between strains
C. Change in host from plant to animal
D. Small mutations in viral RNA

Answer: B

Antigenic shift is reassortment of RNA segments, creating new subtype.

25Which describes the genome of Hepatitis B virus?

A. Partially double-stranded circular DNA
B. Single-stranded RNA
C. Double-stranded RNA
D. Single-stranded linear DNA

Answer: A

HBV has a partially double-stranded circular DNA genome.

✅Practice MCQs — Test 3

🧪 Exam-Level Questions

50 MCQs

1Which is an incorrect statement regarding the viral genome?

A. Can be linear or circular
B. Can be single or double-stranded
C. A single virus can contain both DNA and RNA
D. Genome protected by capsid

Answer: C

Viruses contain either DNA or RNA, never both.

2The number of capsomeres present in the capsid of an Adenovirus:

A. 162
B. 252
C. 122
D. 212

Answer: B. 252

Adenovirus has 252 capsomeres (240 hexons + 12 pentons).

3Which virus is characterized by brick-shaped structure?

A. Influenza virus
B. T4 Bacteriophage
C. Poxvirus
D. Adenovirus

Answer: C. Poxvirus

Poxviruses are brick-shaped or ovoid.

4Viruses that consist of only a nucleocapsid without outer lipid layer are termed:

A. Prions
B. Viroids
C. Naked viruses
D. Lipoviruses

Answer: C. Naked viruses

Naked viruses lack an envelope.

5The symmetry of the Poliovirus is:

A. Helical
B. Complex
C. Icosahedral
D. Binal

Answer: C. Icosahedral

Poliovirus is non-enveloped icosahedral.

6Which is a Double-Stranded RNA virus?

A. HIV
B. Reovirus
C. Hepatitis B virus
D. Influenza virus

Answer: B. Reovirus

Reoviridae (e.g., rotavirus) have dsRNA genomes.

7The viral envelope is usually derived from:

A. Host cell wall
B. Host cell membrane/nuclear membrane
C. Viral protein synthesis
D. Spontaneous assembly

Answer: B

Enveloped viruses acquire lipid envelope from host membranes.

8A bacteriophage consists of head and tail. The DNA is located in the:

A. Tail fibers
B. Sheath
C. Polyhedral head
D. End plate

Answer: C. Polyhedral head

The head contains the viral genome.

9The protein subunits that make up the capsid are known as:

A. Protomeres
B. Capsomeres
C. Viromeres
D. Nucleosomes

Answer: B. Capsomeres

Capsomeres are protein subunits that form the capsid.

10Which is a characteristic of a 'positive-sense' RNA virus?

A. Must be converted to DNA first
B. Acts directly as mRNA upon entering host
C. Requires specialized RNA polymerase
D. Always double-stranded

Answer: B

Positive-sense RNA can be immediately translated by host ribosomes.

11Which of the following contains 162 capsomeres?

A. Adenovirus
B. Herpes virus
C. Hepatitis B
D. Influenza

Answer: B. Herpes virus

Herpesvirus has 162 capsomeres; Adenovirus has 252.

12Reverse Transcriptase is technically a:

A. DNA-dependent RNA polymerase
B. RNA-dependent DNA polymerase
C. RNA-dependent RNA polymerase
D. DNA-dependent DNA polymerase

Answer: B

Synthesizes DNA from RNA template.

13Which is NOT a feature of T4 bacteriophage?

A. Hexagonal head
B. Tail with 6 fibers
C. Single-stranded DNA
D. Lysozyme-like enzyme in tail

Answer: C

T4 phage has double-stranded DNA.

14The chemical nature of viral envelope is:

A. Purely Protein
B. Lipoprotein
C. Glycoprotein and Lipid
D. Polysaccharide

Answer: C

Envelope is lipid bilayer with viral glycoproteins.

15If a virus infects a plant, its genome is most likely:

A. dsDNA
B. ssRNA
C. ssDNA
D. dsRNA

Answer: B. ssRNA

Most plant viruses have ssRNA genomes (e.g., TMV).

16Which is characteristic of Viroids but not Viruses?

A. Presence of capsid
B. Presence of DNA
C. Low molecular weight RNA without protein coat
D. Ability to infect animals

Answer: C

Viroids are circular RNA without protein coat.

17Mumps and Measles are caused by which group of viruses?

A. Paramyxoviruses
B. Orthomyxoviruses
C. Retroviruses
D. Rhabdoviruses

Answer: A. Paramyxoviruses

Both mumps and measles are paramyxoviruses.

18Which is a 'zoonotic' viral disease?

A. Polio
B. Smallpox
C. Rabies
D. Hepatitis C

Answer: C. Rabies

Rabies transmits from animals to humans – a zoonosis.

19Smallpox was globally eradicated in which year?

A. 1970
B. 1980
C. 1995
D. 2000

Answer: B. 1980

WHO declared smallpox eradicated in 1980.

20Which virus is associated with the development of Liver Cancer?

A. HIV
B. Hepatitis B
C. Rhinovirus
D. Epstein-Barr Virus

Answer: B. Hepatitis B

Chronic HBV infection is a major risk for hepatocellular carcinoma.

21HIV specifically attacks cells expressing which surface receptor?

A. CD8
B. CD4
C. MHC II
D. BCR

Answer: B. CD4

HIV binds CD4 on helper T-cells, macrophages, dendritic cells.

22The core of HIV contains how many copies of ssRNA?

A. 1
B. 2
C. 3
D. 4

Answer: B. 2

HIV has two identical copies of positive-sense ssRNA (diploid).

23Which protein on HIV envelope is responsible for initial attachment?

A. gp41
B. gp120
C. p24
D. p17

Answer: B. gp120

gp120 binds CD4 receptor; gp41 then mediates fusion.

24The enzyme Integrase in HIV is used to:

A. Convert RNA to DNA
B. Cleave large polyproteins
C. Incorporate viral DNA into host genome
D. Lyse host cell membrane

Answer: C

Integrase inserts viral cDNA into host chromosome, forming provirus.

25HIV is classified as a:

A. Lentivirus
B. Oncovirus
C. Adenovirus
D. Flavivirus

Answer: A. Lentivirus

HIV is a lentivirus (slow virus) of the retrovirus family.

26In HIV life cycle, 'provirus' state refers to:

A. Virus before entering cell
B. Viral DNA integrated into host chromosome
C. Newly assembled virions
D. RNA-DNA hybrid

Answer: B

Provirus is integrated HIV DNA that replicates with host.

27Which is a common opportunistic infection in AIDS patients?

A. Common Cold
B. Pneumocystis carinii pneumonia
C. Typhoid
D. Cholera

Answer: B

Pneumocystis jirovecii (formerly carinii) pneumonia is an AIDS-defining illness.

28The maturation of HIV proteins (cleaving chains) is performed by:

A. Reverse Transcriptase
B. Integrase
C. Protease
D. Host Ribosomes

Answer: C. Protease

HIV protease cleaves Gag and Gag-Pol polyproteins.

29Which part of HIV fuses with host membrane to allow entry?

A. gp120
B. gp41
C. p24
D. Capsid

Answer: B. gp41

gp41 conformational change pulls membranes together.

30The primary cause of death in AIDS is usually:

A. HIV destroying the brain
B. Secondary opportunistic infections and malignancies
C. Total liver failure
D. Massive hemorrhaging

Answer: B

AIDS patients die from opportunistic infections or cancers.

31Which is NOT a major mode of HIV transmission?

A. Sexual contact
B. Sharing needles
C. Mosquito bites
D. Breastfeeding

Answer: C. Mosquito bites

HIV is not transmitted by mosquitoes.

32The 'window period' in HIV infection refers to:

A. Time virus enters cell
B. Time between infection and detectable antibodies
C. Time when patient not infectious
D. Duration of asymptomatic phase

Answer: B

During window period, antibodies not detectable but person infectious.

33Which cells can also be infected by HIV, acting as a 'reservoir'?

A. Red Blood Cells
B. Macrophages
C. B-lymphocytes
D. Platelets

Answer: B. Macrophages

Macrophages and dendritic cells express CD4 and harbor HIV.

34The major capsid protein of HIV used in diagnostic tests is:

A. p17
B. p24
C. gp120
D. Reverse Transcriptase

Answer: B. p24

p24 antigen tests detect early HIV infection.

35How does HIV typically exit a host T-cell?

A. Lysis (bursting)
B. Budding
C. Exocytosis
D. Passive diffusion

Answer: B. Budding

HIV buds from plasma membrane, acquiring its envelope.

36If a drug blocks gp41, what stage of HIV life cycle is inhibited?

A. Attachment
B. Fusion and Entry
C. Integration
D. Assembly

Answer: B. Fusion and Entry

gp41 mediates fusion; blocking prevents viral entry.

37A virus with lipid envelope, no reverse transcriptase, and dsDNA genome is most likely:

A. HIV
B. Herpes Virus
C. Influenza Virus
D. Polio Virus

Answer: B. Herpes Virus

Herpesvirus is enveloped, dsDNA, lacks reverse transcriptase.

38Which statement is true regarding 'specificity' of viruses?

A. Viruses can infect any cell type
B. Attachment determined by viral proteins and host receptors
C. Plant viruses easily infect animal cells
D. Bacteriophages can treat human viral infections

Answer: B

Viral specificity is due to receptor-ligand interactions (e.g., HIV-CD4).

39Correct sequence of HIV life cycle:

A. Attachment → Integration → Reverse Transcription → Budding
B. Attachment → Reverse Transcription → Integration → Budding
C. Integration → Attachment → Uncoating → Assembly
D. Reverse Transcription → Integration → Attachment → Budding

Answer: B

Attachment, entry, reverse transcription, integration, transcription, assembly, budding.

40Which would be an effective target for a drug against HIV but not harm host cell?

A. Ribosomal protein synthesis
B. ATP production
C. Reverse Transcriptase activity
D. Cell membrane permeability

Answer: C

Reverse transcriptase is viral-specific; human cells lack it. AZT targets it.

41The host range of a virus is determined by:

A. Size of the virus
B. Type of nucleic acid
C. Presence of specific surface receptors on host cell
D. Amount of energy host produces

Answer: C

Viruses infect only cells with compatible receptors (CD4 for HIV).

42A patient has low T-helper count but tests negative for HIV antibodies. This could be because:

A. Patient is in window period
B. Patient has different immunodeficiency
C. Immune system hasn't produced enough antibodies
D. All of the above

Answer: D. All of the above

Window period, other immunodeficiencies, or delayed seroconversion.

43Why are viruses considered non-living by many biologists?

A. Lack metabolic machinery
B. Cannot reproduce independently
C. Can be crystallized
D. All of the above

Answer: D

No metabolism, no independent reproduction, can form crystals.

44Which Hepatitis virus is a DNA virus?

A. Hepatitis A
B. Hepatitis B
C. Hepatitis C
D. Hepatitis E

Answer: B. Hepatitis B

HBV has partially double-stranded DNA. A, C, E are RNA viruses.

45The most common reason for high mutation rate in HIV is:

A. Host cell radiation
B. Lack of proofreading in Reverse Transcriptase
C. Complexity of envelope proteins
D. Presence of two RNA strands

Answer: B

RT has no proofreading, leading to about 1 mutation per genome per cycle.

46Which virus is NOT transmitted by mosquitoes but by direct fluid exchange?

A. Dengue
B. Malaria parasite
C. HIV
D. Yellow fever

Answer: C. HIV

HIV requires direct blood/body fluid exchange, not mosquito vectors.

47Which pair is correctly matched?

A. Adenovirus – enveloped
B. Polio – enveloped
C. HIV – enveloped
D. TMV – enveloped

Answer: C

HIV is enveloped; Adenovirus, Polio, TMV are naked.

48What does 'retro' in retrovirus refer to?

A. Retrograde movement in body
B. Reverse flow of genetic information (RNA→DNA)
C. Retro-viral shape
D. Retro-sterilization

Answer: B

'Retro' refers to reverse transcription – RNA to DNA, opposite of normal flow.

49Which is the smallest known virus?

A. Pox virus
B. Herpes
C. Poliovirus
D. HIV

Answer: C. Poliovirus

Poliovirus (~20-30 nm) is one of the smallest known viruses.

50Which statement about naked viruses is TRUE?

A. They are less stable than enveloped
B. They lack genetic material
C. They are more resistant to heat and detergents
D. They cannot infect host cells

Answer: C

Naked viruses lack lipid envelope, making them more environmentally stable.

📄Past Paper MCQs

📅 Actual MDCAT / NUMS Questions

44 MCQs

1________ of HIV attach to receptors of host cell:

MDCAT 2023

A. RNA
B. Capsid
C. Spikes
D. Matrix

Answer: C. Spikes

gp120 spikes bind to CD4 receptors on host cells.

2In HIV, gp120 is responsible for:

MDCAT 2023

A. Core formation
B. Capsid formation
C. Spike formation
D. Matrix

Answer: C. Spike formation

gp120 forms the spikes that attach to CD4 receptors.

3Which property makes viruses similar to living organisms?

MDCAT 2023

A. Respiration
B. Cytoplasm
C. Mutation
D. Metabolism

Answer: C. Mutation

Viruses can mutate, a characteristic of living organisms.

4First step in bacteriophage replication:

MDCAT 2023

A. Injection
B. Replication
C. Attachment
D. Assembly

Answer: C. Attachment

Attachment (adsorption) is the first step.

5Correct sequence of HIV life cycle:

MDCAT 2023

A. Binding → Fusion → Reverse transcription → Integration → Replication → Assembly → Budding
B. Fusion → Binding → Integration → Replication → Assembly
C. Binding → Replication → Integration
D. Reverse transcription → Binding

Answer: A

Correct order: attachment, fusion, reverse transcription, integration, replication, assembly, budding.

6All viruses are:

NUMS 2023

A. Autotrophs
B. Parasites
C. Predators
D. Saprophytes

Answer: B. Parasites

Viruses are obligate intracellular parasites.

7Complete infective viral particle is called:

NUMS 2023

A. Capsid
B. Genome
C. Virion
D. Envelope

Answer: C. Virion

A virion is a complete, infectious viral particle.

8Enveloped viruses enter host cell by:

MDCAT 2024

A. Injection
B. Diffusion
C. Endocytosis / Fusion
D. Active transport

Answer: C

Enveloped viruses fuse envelope with host membrane or enter via endocytosis.

9Tobacco Mosaic Virus shape is:

MDCAT 2024

A. Spherical
B. Cubical
C. Rod-shaped
D. Spiral

Answer: C. Rod-shaped

TMV is a helical rod-shaped virus.

10HIV primarily infects:

MDCAT 2023

A. RBCs
B. CD4 T cells
C. Platelets
D. Neutrophils

Answer: B. CD4 T cells

HIV targets CD4+ T helper cells.

11Mode of HIV transmission:

NUMS 2023

A. Air
B. Water
C. Blood transfusion
D. Touch

Answer: C. Blood transfusion

HIV is transmitted through blood, sexual contact, and breastfeeding.

12Major cause of death in AIDS:

MDCAT 2024

A. Virus itself
B. Opportunistic infections
C. RBC destruction
D. Fever

Answer: B. Opportunistic infections

AIDS patients die from opportunistic infections due to weakened immunity.

13HIV belongs to:

MDCAT 2023-24

A. DNA virus
B. Retrovirus
C. dsRNA virus
D. Bacteriophage

Answer: B. Retrovirus

HIV is a retrovirus with RNA genome using reverse transcriptase.

14Enzyme converting RNA → DNA in HIV:

NUMS 2024

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

Answer: C. Reverse transcriptase

Reverse transcriptase synthesizes DNA from RNA template.

15Protein coat of virus is called:

MDCAT 2021

A. Envelope
B. Capsid
C. Matrix
D. Core

Answer: B. Capsid

The capsid encloses the viral genome.

16Capsid is made up of:

NUMS 2022

A. Lipids
B. Nucleic acids
C. Capsomeres
D. Enzymes

Answer: C. Capsomeres

Capsomeres are protein subunits of the capsid.

17Genetic material of virus can be:

MDCAT Repeated

A. Only DNA
B. Only RNA
C. Both DNA & RNA (but not together)
D. Proteins

Answer: C

Viruses contain either DNA or RNA, never both.

18Which virus lacks envelope?

NUMS 2021

A. HIV
B. Influenza
C. Adenovirus
D. Herpes

Answer: C. Adenovirus

Adenovirus is a non-enveloped (naked) virus.

19Viral nucleic acid is enclosed in:

MDCAT Concept

A. Envelope
B. Capsid
C. Cytoplasm
D. Cell wall

Answer: B. Capsid

The capsid directly encloses the viral genome.

20Viruses can be crystallized because they:

MDCAT 2020

A. Are living
B. Have metabolism
C. Are non-living outside host
D. Have nucleus

Answer: C

Outside a host, viruses are inert and can form crystals.

21Which virus infects plants?

NUMS Pattern

A. HIV
B. TMV
C. T4 phage
D. Influenza

Answer: B. TMV

TMV infects plants.

22Shape of bacteriophage is:

MDCAT Concept

A. Rod
B. Helical
C. Complex
D. Spherical

Answer: C. Complex

Bacteriophages have complex (binal) symmetry.

23Viral envelope is derived from:

NUMS 2022

A. Viral DNA
B. Host cell membrane
C. Capsid
D. Ribosomes

Answer: B

Enveloped viruses acquire lipid envelope from host membranes.

24Which is NOT a viral disease?

MDCAT Repeated

A. AIDS
B. Polio
C. Tuberculosis
D. Influenza

Answer: C. Tuberculosis

TB is caused by bacteria (Mycobacterium tuberculosis).

25HIV destroys which immune cells?

MDCAT 2021

A. B cells
B. CD8 cells
C. CD4 T cells
D. Macrophages

Answer: C. CD4 T cells

HIV primarily destroys CD4+ T helper cells.

26Window period in HIV means:

NUMS 2022

A. Virus absent
B. Symptoms absent but virus present
C. Immunity high
D. No infection

Answer: B

Window period: virus present but antibodies not yet detectable.

27Which enzyme helps HIV integrate into host genome?

MDCAT Concept

A. Ligase
B. Integrase
C. Helicase
D. Polymerase

Answer: B. Integrase

Integrase inserts viral DNA into the host chromosome.

28Protease in HIV is important for:

NUMS Repeated

A. DNA synthesis
B. Protein maturation
C. Entry
D. Attachment

Answer: B. Protein maturation

Protease cleaves polyproteins into functional viral proteins.

29Reverse transcriptase converts:

MDCAT 2022-24

A. DNA → RNA
B. RNA → DNA
C. Protein → DNA
D. DNA → Protein

Answer: B. RNA → DNA

Reverse transcriptase synthesizes DNA from RNA.

30AIDS is characterized by:

MDCAT Concept

A. Increased immunity
B. Autoimmunity
C. Immunodeficiency
D. Allergy

Answer: C. Immunodeficiency

AIDS causes severe immunodeficiency due to CD4+ T cell loss.

31Which is NOT a mode of HIV transmission?

NUMS Pattern

A. Blood transfusion
B. Sexual contact
C. Sharing needles
D. Handshake

Answer: D. Handshake

HIV is not transmitted by casual contact.

32Which organ/system is mainly affected in AIDS?

MDCAT Repeated

A. Nervous
B. Digestive
C. Immune
D. Circulatory

Answer: C. Immune

HIV attacks the immune system.

33HIV infection leads to decrease in:

NUMS Concept

A. RBC
B. Platelets
C. CD4 count
D. Hemoglobin

Answer: C. CD4 count

HIV causes progressive decline in CD4+ T cell count.

34Which virus contains single-stranded DNA?

Predicted 2026

A. Adenovirus
B. Herpes virus
C. Parvovirus
D. Pox virus

Answer: C. Parvovirus

Parvoviruses have single-stranded DNA genomes.

35Which structure protects viral nucleic acid?

Predicted 2026

A. Envelope
B. Capsid
C. Matrix
D. Spike

Answer: B. Capsid

Capsid encloses and protects viral genome.

36Which virus has helical symmetry?

Predicted 2026

A. Adenovirus
B. HIV
C. TMV
D. Bacteriophage

Answer: C. TMV

TMV is a classic helical virus.

37Which of the following is non-enveloped virus?

Predicted 2026

A. HIV
B. Influenza
C. Adenovirus
D. Herpes

Answer: C. Adenovirus

Adenovirus lacks an envelope.

38Viruses are considered non-living because they lack:

Predicted 2026

A. DNA
B. Protein
C. Metabolism
D. Capsid

Answer: C. Metabolism

Viruses have no independent metabolism.

39First step in viral infection is:

Predicted 2026

A. Penetration
B. Attachment
C. Replication
D. Assembly

Answer: B. Attachment

Attachment to host receptors is the initial step.

40Which virus has complex structure?

Predicted 2026

A. TMV
B. HIV
C. Adenovirus
D. Bacteriophage

Answer: D. Bacteriophage

Bacteriophages have complex (binal) symmetry.

41Function of integrase enzyme is:

Predicted 2026

A. Protein synthesis
B. RNA replication
C. Integration into host DNA
D. Attachment

Answer: C. Integration into host DNA

Integrase integrates viral DNA into the host genome.

42Protease enzyme in HIV helps in:

Predicted 2026

A. DNA formation
B. Viral protein maturation
C. Entry
D. Attachment

Answer: B. Viral protein maturation

Protease cleaves polyproteins to mature viral proteins.

43HIV life cycle includes which unique step?

Predicted 2026

A. Translation
B. Reverse transcription
C. Replication
D. Assembly

Answer: B. Reverse transcription

Reverse transcription is unique to retroviruses like HIV.

44Which is the most reliable confirmatory test for HIV?

Predicted 2026

A. ELISA
B. Western blot
C. PCR only
D. Biopsy

Answer: B. Western blot

ELISA is the screening test; Western blot confirms the diagnosis.

🔍Direct Search Queries — Biodiversity & Viruses

Exact search terms students use on Google for this chapter. Click any to jump to the relevant section:

biodiversity MDCAT notes virus classification MDCAT types of viruses in biology classification of viruses chart virus structure and function capsid and capsomere difference naked vs enveloped virus helical vs icosahedral symmetry Tobacco Mosaic Virus notes bacteriophage T4 structure what is HIV virus HIV structure diagram gp120 gp41 p24 HIV HIV life cycle steps AIDS transmission routes AIDS symptoms in men and women window period HIV meaning provirus vs prophage reverse transcriptase function ELISA test full form HIV Pneumocystis jirovecii AIDS Kaposi sarcoma AIDS cancer what is biodiversity definition difference virus vs bacteria DNA vs RNA virus difference how many MCQs from biology in MDCAT how many chapters in MDCAT biology biodiversity weightage MDCAT biodiversity MCQs with answers biodiversity MCQs pdf HIV AIDS MCQs with answers MDCAT past papers biodiversity UHS MDCAT biology MCQs NUMS biology past papers biodiversity chapter 1 class 11 notes virus notes class 11 biology prions viroids differences lysogenic vs lytic cycle

❔Frequently Asked Questions

What is biodiversity in simple words?

Biodiversity is the variety of all living things on Earth — plants, animals, microorganisms, and the ecosystems they form. In MDCAT Chapter 1, it specifically covers virus classification and AIDS.

How are viruses classified in MDCAT?

Viruses are classified on five bases: by structure/symmetry, by nucleic acid, by host, by envelope, and by disease caused.

Do viruses contain both DNA and RNA?

No. A virus contains either DNA or RNA, never both. HIV has ssRNA; Adenovirus has dsDNA.

What is the structure of HIV?

HIV is enveloped retrovirus with: two copies of ssRNA, reverse transcriptase/integrase/protease, conical p24 capsid, envelope with gp120 (attachment) and gp41 (fusion). Targets CD4+ helper T-cells.

How is HIV transmitted?

Through unprotected sexual contact, blood transfusion/needles, and mother-to-child. NOT by mosquito bites, handshakes, food sharing, or coughing.

What is the window period in HIV?

Time after infection when virus is present but antibodies are not yet detectable (2–4 weeks). Person is infectious during this period.

What is a provirus?

HIV viral DNA integrated into the host genome by integrase. Replicates with host chromosome, can remain latent for years.

What is the difference between provirus and prophage?

Provirus is integrated viral DNA of an animal virus (HIV). Prophage is integrated phage DNA in a bacterium. Both represent dormant lysogenic state.

Which virus causes AIDS?

HIV — a retrovirus with ssRNA that attacks CD4+ helper T-cells.

What is the shape of Tobacco Mosaic Virus?

TMV has helical (rod-shaped) symmetry with ssRNA. First virus discovered by Iwanowsky in 1892.

What is the shape of a bacteriophage?

Bacteriophages have complex (binal) symmetry: icosahedral head + helical tail.

Which viruses are naked (non-enveloped)?

Naked viruses lack a lipid envelope: Adenovirus, Poliovirus, TMV. More resistant to heat and detergents.

What enzyme does HIV use to convert RNA to DNA?

Reverse transcriptase (RNA-dependent DNA polymerase) converts HIV's ssRNA into DNA.

Which test is used to screen for HIV?

ELISA is the screening test. Western blot confirms. p24 antigen test detects early infection.

Do AIDS patients die from HIV itself?

AIDS patients typically die from secondary opportunistic infections (Pneumocystis pneumonia, TB) or malignancies (Kaposi's sarcoma), not HIV itself.

Which viral disease is transmitted by animals (zoonotic)?

Rabies — transmitted from animals (dogs, bats) to humans. Causes hydrophobia and is almost always fatal.

How many MCQs come from Biodiversity in MDCAT?

Biodiversity typically contributes 4–6 MCQs in MDCAT Biology.

What is the difference between lytic and lysogenic cycle?

Lytic cycle: virus replicates and destroys host cell. Lysogenic cycle: viral DNA integrates as prophage and replicates passively.

Are viroids the same as viruses?

No. Viroids are circular ssRNA molecules with no protein coat — they only infect plants. Viruses always have a capsid.

What are prions?

Prions are infectious misfolded proteins with no nucleic acid. They cause neurodegenerative diseases like mad cow disease and Creutzfeldt-Jakob disease.

Biodiversity — Viruses & AIDS (Complete MDCAT Notes)

⚡Quick Answers to Common Searches

What is biodiversity?

What is a virus?

How many types of viruses are there?

Do viruses have DNA or RNA?

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What is a capsid?

What does HIV stand for?

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How is HIV transmitted?

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What is a provirus?

What does reverse transcriptase do?

Virus vs bacteria?

How many MCQs from Biodiversity?

❓People Also Ask — Biodiversity & HIV/AIDS

📋Syllabus & Learning Outcomes

📝Full Notes — Virus Classification & HIV/AIDS

1.1 Classification of Viruses

A. By Structure / Symmetry

B. By Nucleic Acid (Strands)

C. By Host

D. By Envelope

E. By Disease

1.2 AIDS — Cause, Transmission & Symptoms

Causative Agent

Modes of Transmission

Symptoms & Stages

Diagnosis

HIV Life Cycle

High-Yield Points & Common Traps

✅Practice MCQs — Test 1

🧪 Basic Concepts

✅Practice MCQs — Test 2

🧪 Advanced Concepts

✅Practice MCQs — Test 3

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