Which of the following statements is/are correct? 1. Viruses lack enzymes necessary for the generation of energy 2. Viruses can be cultured in any synthetic medium. 3. Viruses are transmitted from one organism to another by biological vectors only Select the correct answer using the codes given below.
Contents16
- A1 only
- B2 and 3 only
- C1 and 3 only
- D1, 2 and 3
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Answer: (A) 1 only
Statement 1 is correct — viruses do not have the chemical machinery (enzymes, ribosomes, mitochondria) needed to generate energy on their own.
They are essentially just genetic material (DNA or RNA) wrapped in a protein coat.
Statement 2 is wrong — viruses CANNOT be cultured in synthetic media (like agar).
Unlike bacteria, which can grow independently on synthetic media, viruses need living host cells to multiply.
They can only be grown on cultures of living cells (tissue culture).
This is because viruses hijack the host cell's machinery to replicate.
Statement 3 is wrong — viruses are NOT transmitted only by biological vectors.
They can also spread through:
- air (airborne)
- water
- direct contact
- fomites (contaminated surfaces)
- bodily fluids
- even through breaks in the skin.
Mosquito-borne transmission is just one of many routes.
So only statement 1 is correct.
Viruses are obligate parasites that cannot survive or reproduce without hijacking a living host cell's machinery, unlike bacteria which can grow independently.
The question tests the fundamental difference between viruses and bacteria - viruses need living cells to replicate while bacteria can multiply on artificial media like agar plates.
UPSC is checking if students understand virus transmission modes beyond just vector-borne diseases, since viruses spread through multiple routes including air, water, and direct contact.
Virus Structure & Metabolism
Science And Technology Viruses lack enzymes generation of energy
Virus Structure & Metabolism: Why Viruses Cannot Generate Energy
Viruses lack enzymes necessary for energy generation
Viruses contain only genetic material (DNA/RNA) + protein coat
Viruses are obligate intracellular parasites - must hijack host cell machinery
No ribosomes, mitochondria, or metabolic enzymes in viruses
What Viruses Actually Are
Viruses are non-cellular entities consisting of genetic material wrapped in a protein coat (capsid). Unlike living cells, they lack the basic cellular machinery needed for independent life.
Virus vs Cell Structure
Component | Virus | Living Cell | Significance |
|---|---|---|---|
Enzymes | Absent | Present | Cannot generate ATP energy |
Ribosomes | Absent | Present | Cannot synthesize proteins |
Mitochondria | Absent | Present (eukaryotes) | No cellular respiration |
Cell membrane | Absent | Present | No selective permeability |
Genetic material | DNA or RNA | DNA + RNA | Only component for reproduction |
Why Energy Generation Is Impossible
No glycolytic enzymes - cannot break down glucose for energy
No electron transport chain - cannot produce ATP through oxidative phosphorylation
No metabolic pathways - completely dependent on host cell's energy systems
Must hijack host ribosomes to synthesize viral proteins
Trap: Don't confuse viruses with bacteria - bacteria have enzymes and can generate energy independently
Trap: Viruses are not living organisms - they lack metabolism, the key characteristic of life
Trap: Statement 1 is correct - this tests understanding of viral dependence on host machinery
Virus Cultivation Methods
Science And Technology cultured in any synthetic medium
Virus Cultivation: Why Synthetic Media Cannot Work
Viruses CANNOT be cultured in synthetic media like agar
Viruses need living host cells for cultivation
Tissue culture is the primary method for virus cultivation
Unlike bacteria, viruses cannot grow independently
Why Synthetic Media Fails
Synthetic media (like nutrient agar) provides nutrients for independent organisms. Viruses cannot use these nutrients because they lack the cellular machinery to process them - they need a living cell's complete metabolic system.
Cultivation Methods Comparison
Organism | Culture Medium | Requirements | Growth Pattern |
|---|---|---|---|
Bacteria | Synthetic media (agar plates) | Nutrients + optimal pH/temperature | Independent colonies |
Viruses | Living tissue culture | Host cells + nutrients for host | Inside host cells only |
Fungi | Synthetic media | Organic nutrients + moisture | Independent hyphae/colonies |
Protozoa | Liquid synthetic media | Nutrients + appropriate salinity | Independent multiplication |
Virus Cultivation Techniques
Tissue culture - growing viruses in living cell lines (most common method)
Embryonated eggs - using fertilized chicken eggs as living host system
Laboratory animals - infecting live animals for virus propagation
Cell-free systems - recent technique using extracted cellular components
Trap: Statement 2 is WRONG - viruses cannot be cultured in ANY synthetic medium
Trap: Don't confuse with bacteria - bacteria grow on agar plates, viruses do not
Trap: 'Any synthetic medium' is the key phrase - makes this statement absolutely false
Virus Transmission Modes
Science And Technology transmitted biological vectors only
Virus Transmission: Multiple Routes Beyond Biological Vectors
Viruses are NOT transmitted by biological vectors only
Multiple transmission routes exist: airborne, contact, fomites, fluids
Biological vectors are just one of many transmission methods
Transmission route depends on virus type and environmental stability
Beyond Vector Transmission
Biological vectors (like mosquitoes) are living organisms that carry viruses between hosts. However, this is just one route among many - viruses have evolved diverse transmission strategies depending on their structure and target organs.
Major Virus Transmission Routes
Transmission Mode | Mechanism | Example Viruses | Key Features |
|---|---|---|---|
Airborne | Respiratory droplets/aerosols | Influenza, COVID-19 | Most common route |
Direct Contact | Skin-to-skin contact | Herpes, HPV | Requires physical contact |
Fomites | Contaminated surfaces | Norovirus, Rhinovirus | Indirect contact transmission |
Biological Vectors | Living carriers (mosquitoes) | Dengue, Zika, Chikungunya | Vector must be infected |
Bodily Fluids | Blood, saliva, sexual contact | HIV, Hepatitis B | Fluid exchange required |
Food/Water | Contaminated ingestion | Hepatitis A, Rotavirus | Fecal-oral route |
Why Multiple Routes Exist
Respiratory viruses prefer airborne transmission for lung access
Skin viruses use direct contact for surface infection
Enteric viruses survive in water/food for gastrointestinal infection
Vector-borne viruses exploit insect feeding patterns for blood access
Trap: Statement 3 is WRONG - 'only by biological vectors' makes it false
Trap: Don't forget airborne transmission - most common viral transmission route
Trap: COVID-19 is a recent example of non-vector viral transmission that UPSC may reference
Obligate Parasites Concept
Science And Technology
Obligate Parasites: Understanding Complete Host Dependence
Obligate parasites cannot survive without a host organism
Viruses are the most extreme example of obligate parasitism
Facultative parasites can live independently or as parasites
Obligate nature explains why viruses cannot be cultured artificially
Defining Obligate Parasitism
Obligate parasites are organisms that have evolved to be completely dependent on host organisms for survival and reproduction. They cannot complete their life cycle without a host.
Types of Parasites by Host Dependence
Parasite Type | Host Dependence | Examples | Survival Without Host |
|---|---|---|---|
Obligate Intracellular | Must live inside host cells | Viruses, Chlamydia | Cannot survive |
Obligate Extracellular | Must live on/in host but outside cells | Plasmodium (some stages) | Very limited survival |
Facultative | Can live with or without host | Some bacteria, fungi | Can survive independently |
Free-living | No parasitic requirement | Most bacteria | Independent survival |
Viral Obligate Characteristics
# Virus Obligate Nature
## Structural Dependence
- No ribosomes
- No enzymes
- No cell membrane
- Only genetic material
## Metabolic Dependence
- Host ATP required
- Host protein synthesis
- Host replication machinery
## Reproductive Dependence
- Host cell division
- Host transcription factors
- Host translation systemTrap: All three statements connect to viral obligate nature - understand the underlying concept
Trap: Don't confuse obligate (must have host) with facultative (can choose host or independence)
Trap: Obligate nature explains why synthetic media fails and why energy generation is impossible