This MCQ module is based on: Immunity, Vaccines and Prevention
TOPIC 8 OF 50
Immunity, Vaccines and Prevention
🎓 Class 8
Science
CBSE
Theory
Ch 3 — Synthetic Fibres and Plastics
⏱ ~28 min
🌐 Language: [gtranslate]
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3.4 Body's Defence System
If pathogens are everywhere — in the air, on door handles, in water — why are we not sick all the time? Because the human body is a brilliantly guarded fortress. It has two main walls of defence: an outer wall that keeps invaders out, and an inner wall that fights those that slip through.
A. Outer Defence — The First Line
Skin
A tough, waterproof barrier that blocks most microbes. Cuts break this barrier — that is why we clean wounds.
Mucus in nose
Sticky mucus traps dust and germs in the nose before they reach the lungs.
Cilia in airways
Tiny hair-like structures sweep trapped germs upward to be coughed out.
Tears
Contain an enzyme called lysozyme that kills bacteria on the eye's surface.
Stomach acid
Strongly acidic — destroys most pathogens we swallow with food.
Healthy gut bacteria
Friendly microbes in our intestine outcompete harmful ones for food and space.
B. Inner Defence — The Immune System
When pathogens slip past the outer walls, the immune system takes over. Its main soldiers and weapons are:
- White Blood Cells (WBCs): roving warriors that engulf and digest pathogens.
- Lymph nodes: small bean-shaped filters (in the neck, armpits, groin) that trap pathogens. When you're sick, these can swell — that's them working hard!
- Antibodies: Y-shaped proteins that lock onto pathogens, mark them, and neutralise them.
Innate vs Acquired Immunity
| Innate immunity | Acquired immunity |
|---|---|
| Born with it. General defence against all invaders. Acts immediately. | Develops after exposure to a specific pathogen. Slower first time — but strong and long-lasting. |
| Example: skin, stomach acid, fever response. | Example: immunity after recovering from chickenpox; immunity from vaccines. |
Acquired immunity has a special superpower: memory cells. Once the body has seen a pathogen, it remembers. Next time that same germ appears, the response is lightning-fast — often stopping disease before you even feel sick.
3.5 How to Prevent and Control Diseases
Prevention is better than cure! It is cheaper, faster, and spares you the suffering of being sick.
A. Preventing Communicable Diseases
1. Personal Hygiene
Handwashing
With soap, for 20 seconds. The single most powerful disease-prevention habit.
Daily bath
Removes sweat, dirt, and microbes from the skin.
Brush twice daily
Prevents tooth decay and gum disease.
Cut nails
Dirt and germs hide under long nails and enter with food.
2. Clean Water, Food, and Environment
- Water: boil, filter, or chlorinate water before drinking.
- Food: keep it covered, wash fruits and vegetables, cook meat and eggs thoroughly.
- Environment: dispose of waste properly; don't let water stagnate (where mosquitoes breed); use nets.
3. Vaccination (Immunisation)
A vaccine is like a safe "training drill" for your immune system. It contains weakened or killed pathogens (or tiny pieces of them). When injected:
- The body recognises these as invaders and makes antibodies against them.
- Memory cells are formed and stored.
- If the real pathogen attacks later, memory cells fire a fast, strong response — disease is prevented.
India's National Immunisation Programme
Every child in India is offered free vaccines against many deadly diseases:
🏆 India's Polio Victory: In 1995, India launched the Pulse Polio campaign — teams went door-to-door to give every child under 5 a drop of polio vaccine. Over two decades, millions of volunteers, booth workers, and health officials vaccinated billions of children. In 2014, the WHO declared India polio-free — one of the greatest public health successes in human history.
4. Medicines and Quarantine
- Antibiotics — kill bacteria (TB, typhoid). They do NOT work on viruses.
- Antivirals — slow down viruses (flu, HIV, COVID-19).
- Antifungals — treat fungal infections (ringworm).
- Antiparasitics — fight protozoa (malaria) and worms.
- Quarantine/Isolation: keeping infected people apart during outbreaks to break the chain of spread.
B. Preventing Non-Communicable Diseases
- Balanced diet — whole grains, dal, vegetables, fruits, milk; less salt, sugar, and fried food.
- Regular exercise — at least 30 minutes a day for adults, 60 minutes for children.
- Adequate sleep — 8–10 hours for teenagers; vital for immunity too.
- Stress management — yoga, meditation, hobbies, time with loved ones.
- No tobacco, no alcohol — both cause cancer, heart disease, liver damage.
- Regular health check-ups — catch problems early.
🛡️ Prevention Pyramid
📖 Story — Odisha's Sanitation Success: A decade ago, many villages in Odisha faced repeated outbreaks of cholera and diarrhoea. A community-led sanitation campaign built toilets in every household, taught handwashing in schools, and ensured safe drinking water through chlorination. Within a few years, water-borne diseases dropped sharply, school attendance rose, and healthcare costs fell. Simple, local, powerful.
🎯 Interactive: Build Your Immunity Plan L3 Apply
Tick the activities you do every day. See your health score!
Your immunity score: 0 / 10 — Start ticking!
🔬 Activity 3.2 — Handwashing InvestigationL3 Apply
🤔 Predict first: If you simply rinse your hands in water vs use soap and water for 20 seconds — how different will they really be?
- Coat your palms lightly with turmeric (haldi) powder.
- Partner A: rinse hands in water only, for 5 seconds.
- Partner B: use soap + water, rubbing for 20 seconds (sing "Happy Birthday" twice).
- Press both palms onto a clean sheet of white paper. Compare the yellow marks.
- Turmeric acts like invisible germs. Which method cleans better?
Result: The water-only hand still leaves a strong yellow stain; the soap-washed hand leaves almost none. Soap molecules break the oily film that holds dirt/germs to the skin, allowing them to rinse away. This single habit can cut stomach infections in a community by over 40%.
📋 Competency-Based Questions
Arjun's little sister Rhea, aged 4, is due for her MMR booster vaccine. Their neighbour suggests skipping it, saying "she never gets sick, so she doesn't need it." Arjun, now in Class 8, has been reading about vaccines and wants to respond with science.
Q1. L2 Understand Vaccines protect us mainly because they:
Answer: B. Vaccines expose the immune system to a safe form of the pathogen, producing antibodies and memory cells that stop real infections later.
Q2. L1 Remember Name any four components of the body's outer defence. (2 marks)
Answer: Skin; mucus in nose; cilia in airways; tears containing lysozyme; stomach acid; healthy gut bacteria. (Any four.)
Q3. L3 Apply Why do lymph nodes in your neck sometimes swell when you have a sore throat? (3 marks)
Answer: Lymph nodes filter pathogens and house immune cells. During a throat infection, pathogens travel to nearby neck lymph nodes; the nodes fill with WBCs multiplying to fight the infection, causing visible swelling.
Q4. L5 Evaluate Arjun's neighbour says Rhea doesn't need a booster because "she's never been sick". Evaluate this advice using your understanding of memory cells. (3 marks)
Answer: The neighbour is wrong. Rhea has not been sick precisely because her earlier vaccines created antibodies and memory cells that protect her. Over time, memory-cell protection can fade; a booster refreshes it. Skipping boosters leaves gaps in immunity and risks outbreaks of preventable diseases.
Q5. L6 Create HOT: Design a one-day hygiene campaign for a primary school. List three activities. (3 marks)
Hint: (1) Turmeric-handwashing demo (above). (2) Poster competition: "Cover Your Cough". (3) Classroom pledge: nails cut, bath daily, shoes clean; parents briefed at dispersal.
🔗 Assertion–Reason Questions
Assertion (A): Taking antibiotics will cure a common cold faster.
Reason (R): Antibiotics act only against bacteria, while the common cold is caused by a virus.
Answer: D. A is false — antibiotics do not help viral colds. R is true, and it actually explains why A is false.
Assertion (A): Memory cells allow the body to respond faster to a pathogen it has encountered before.
Reason (R): Memory cells store the "pattern" of the pathogen and multiply rapidly on re-exposure.
Answer: A. Both correct; the reason is exactly why acquired immunity is so powerful.
Assertion (A): India's polio eradication was achieved without vaccines.
Reason (R): The Pulse Polio campaign delivered oral polio vaccine to billions of children door-to-door.
Answer: D. A is false — vaccines were central to eradication. R is true and disproves A.
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