Viruses

• Viruses — microscopic agents on border of living/non-living.
• Not true cells — need host cell to reproduce.
• Cause diseases: common cold, influenza, polio, COVID-19.
• Prevention — vaccination, hygiene, safe water.

1. Nature — genetic material (DNA/RNA) in protein coat; obligate parasites.
2. Reproduction — only inside living host cells; hijack cell machinery.
3. Diseases — viral: flu, measles, hepatitis; bacterial different (tuberculosis).
4. Antibiotics — ineffective against viruses.
5. Vaccines — weakened/inactivated virus triggers immunity (polio drops).
6. Real world — handwashing; ORS for dehydration; immunisation programmes.

Why antibiotics don't cure common cold

Step 1 — Common cold mostly viral (rhinovirus etc.).
Step 2 — Antibiotics target bacterial cell wall/metabolism.
Step 3 — Viruses use host cells — antibiotics don't kill them.
Step 4 — Rest, fluids, doctor advice; misuse of antibiotics causes resistance.

• Using antibiotics for every fever (may be viral).
• Misconception: viruses are smaller bacteria (different structure, not cells).
• Thinking vaccine cures active disease always (mainly prevents).
• Confusing bacteria in curd with viral infection.

• Why are viruses called obligate parasites?
• Name two viral diseases.
• How do vaccines help?

Open the Practice tab for graded questions on Viruses.