13 marksCuriosity Grade 8, Chapter 3, page 28
How does your body respond to an infection such as the common cold?
Hint. The unpleasant part of being ill is not only the germ — some of it is your own body at work.
The body has a defence system of its own. The chapter calls the natural ability of the body to fight disease immunity, carried out by the immune system. When a cold virus enters the respiratory tract, that system goes to work.
What you notice, and what it means:
| What you feel | What is happening |
|---|
| Nasal congestion and discharge | The lining produces extra mucus, which traps and flushes out the virus |
| Sore throat, cough | The airway is inflamed and irritated; coughing clears it |
| Fever | The body raises its temperature, which makes conditions less comfortable for the pathogen |
| Body ache, tiredness | Energy is being diverted to the immune response, which is why rest helps |
Symptoms are not the same as the disease. Much of what you feel is your body responding, not the virus acting directly. That is why the chapter says staying at home and resting when unwell helps the body recover — and also minimises spreading the disease to others.
And why the second time is easier. Once the immune system has met a pathogen, it recognises it again. The response on a later exposure is much stronger and faster — the principle vaccines exploit.
✦ Answer: the immune system fights the infection, and most of the symptoms — mucus, cough, fever, aches and tiredness — are that defence at work rather than the virus itself, which is why rest helps recovery and why a later exposure to the same pathogen produces a much stronger response.
24 marksCuriosity Grade 8, Chapter 3, page 28
We rarely see cases of smallpox or polio these days, but diseases like diabetes and heart problems are more common. Why?
Hint. The two halves of this question have completely different answers.
The two halves are unrelated, and that is the point.
Why smallpox and polio have retreated — vaccination. Both are communicable diseases caused by pathogens, and both are vaccine-preventable. Vaccines train the immune system to recognise and attack the germ, giving acquired immunity before any exposure. Mass vaccination eventually eradicated smallpox worldwide — the chapter's own graph shows countries reporting smallpox falling away after the 1965 vaccine campaign until eradication in 1979. Because vaccination also stops transmission, protecting enough people protects everyone.
Why diabetes and heart disease have risen — how we live. These are non-communicable diseases (NCDs). No germ causes them and no vaccine can prevent them. The chapter gives the reasons directly: people are eating more processed food, getting less exercise, and living longer lives. Today most deaths in India are caused by NCDs, and India now has one of the highest numbers of people with diabetes in the world.
The underlying shift. Medicine got very good at the problems caused by pathogens, because those have a clear cause you can vaccinate against or treat. NCDs build up slowly out of diet, activity, weight and environment, so they cannot be solved by a single injection — only by changing habits over years.
✦ Answer: smallpox and polio are communicable and vaccine-preventable, so mass vaccination has driven them down (smallpox was eradicated in 1979); diabetes and heart disease are non-communicable, caused by processed food, less exercise and longer lifespans, and no vaccine can prevent them.
33 marksCuriosity Grade 8, Chapter 3, page 28
Could climate change lead to new types of diseases?
Hint. Think about the diseases in Table 3.1 that depend on an insect, and what those insects need.
The clearest route is through vectors. Malaria and dengue are carried by mosquitoes — insects the chapter calls vectors. Mosquitoes need warmth and still water to breed. If temperatures rise, or rainfall patterns shift, then:
- mosquitoes can survive in places that were previously too cold for them, so diseases appear in regions that never had them
- the breeding season lengthens, so more generations of mosquitoes each year
- heavier or more erratic rain leaves more standing water for breeding
Other plausible routes. Floods can contaminate drinking water with sewage, which spreads the water-borne diseases in Table 3.1 — cholera, typhoid, hepatitis A. Droughts reduce clean water for washing and sanitation. Heat itself worsens non-communicable conditions, and air pollution aggravates asthma.
Being careful with the wording. 'New types of diseases' is a strong claim. What the reasoning above supports confidently is that climate change can change where, when and how much existing diseases occur. Whether genuinely new diseases emerge is a harder question that scientists are actively researching, and it would be overstating the evidence to answer it as settled.
✦ Answer: yes, mainly by changing where and when existing diseases occur — warmer, wetter conditions let mosquito vectors spread into new areas and breed for longer, and floods spread water-borne diseases; whether wholly new diseases emerge is still an open research question rather than a settled fact.
43 marksCuriosity Grade 8, Chapter 3, pages 28-29
How do emotions like stress or worry affect us and make us sick?
Hint. The chapter's opening case study is entirely about this.
Because health is not only physical. The WHO defines health as 'a state of complete physical, mental, and social well-being, and not merely the absence of disease'. Mental and social well-being are part of the definition, not extras.
The chapter's own case (Activity 3.1). A Grade 8 student moved to a new school in another city. With no friends and busy parents, he felt lonely. He coped by spending more time on his phone and social media, which made him feel worse. He stopped trying to make friends — and then came physical effects: headaches, weight loss, and inability to sleep well.
Read the chain carefully. Loneliness (social) → low mood and withdrawal (mental) → more screen time (habit) → headaches, weight loss, poor sleep (physical). Nothing infected him. His body was affected through his circumstances and his habits.
Why poor sleep matters especially. Sleep is when the body and mind rest and recover, so losing it weakens everything else — which is how worry turns into physical illness.
What helped. A doctor advised less screen time and meeting a counsellor, and the school counsellor arranged support to help him make friends. The treatment addressed the social and mental causes, not just the headaches.
✦ Answer: stress and worry are part of health because health includes mental and social well-being — as the chapter's case shows, loneliness led to withdrawal and excess screen time, which produced headaches, weight loss and sleeplessness, and the cure was counselling and friendship rather than medicine.
54 marksCuriosity Grade 8, Chapter 3, page 28
Why do some groups of people get affected more than others during disease outbreaks?
Hint. Look at the preventive measures in Table 3.1 and ask who can actually follow them.
Because prevention depends on circumstances, not only on knowledge. Look at what Table 3.1 recommends — boiled drinking water, properly cooked food, personal hygiene, isolation of patients, mosquito nets, vaccination. Each of those assumes something:
| Preventive measure | What it quietly requires |
|---|
| Boiled drinking water | Fuel, time, a safe water source |
| Isolation of the patient | A separate room — not possible in crowded housing |
| Mosquito nets and repellents | Money to buy them |
| Vaccination | A health centre within reach, and time to get there |
| Staying home when unwell | Being able to afford to miss work |
Environment matters too. The chapter's two playgrounds make the point: people living near dirty, unhygienic surroundings full of flies and mosquitos fall sick more often. Poor sanitation is exactly why the Odisha campaign to build and use toilets reduced diarrhoea and infections.
And some people are more vulnerable. Immunity varies — the chapter notes that some people get sick more often than others although living in a similar environment. The very young, the elderly, and those already ill with a chronic disease are less able to fight off an infection. Poor nutrition weakens defences further.
✦ Answer: because living conditions, sanitation, crowding, income and access to healthcare decide whether preventive measures are even possible, and because immunity varies — the very young, the elderly, the undernourished and the chronically ill are more vulnerable.
Solutions written by the tuition.in editorial team and checked against NCERT Curiosity - Textbook of Science for Grade 8 (hecu103.pdf), Chapter 3 'Health: The Ultimate Treasure', pages 28-45, Reprint 2026-27. HAND-WRITTEN throughout. Page count verified against the printed contents page (hecu1ps.pdf p.18): 18 pages, 28-45, matching exactly. Covers the 5 'Probe and ponder' prompts (p.28), all 7 activities (3.1-3.7), every in-text section (3.1-3.5.1), both 'Our scientific heritage' boxes (Ayurveda; variolation and teekedaars), both 'Be a scientist' boxes (Kamal Ranadive; Maharaj Kishan Bhan), both 'Think like a scientist' boxes (Jenner; Fleming), the 'Ever heard of' box on India's vaccine production, the 11 numbered 'Keep the curiosity alive' exercises (pp.42-45) and the 5 'Discover, design, and debate' projects (p.45). ALL OF TABLE 3.1 TRANSCRIBED FROM THE PDF rather than from memory - 10 diseases with causal agent, site of infection, symptoms and preventive measures, in the book's own three groupings (air-spread: common cold and influenza, chickenpox, measles, tuberculosis; water- and food-spread: hepatitis A, cholera, typhoid, ascariasis; insect-transmitted: malaria, dengue). Exercise Q7's dengue figures were transcribed and re-read: Jan 10, Feb 12, Mar 15, Apr 18, May 22, Jun 40, Jul 65, Aug 65, Sep 65, Oct 30, Nov 30, Dec 20 - so the three peak months are July, August and September at 65 each and the lowest is January at 10, with the rise beginning in June and the fall in October, which matches the monsoon and is the basis of the answer to (iii). Exercise Q10 was answered by route of transmission using Table 3.1: hepatitis A, poliomyelitis and cholera spread by faecal contamination of water, while tuberculosis and chickenpox are airborne and do not. THREE POINTS OF DELIBERATE CAUTION. (1) The 'could climate change lead to NEW types of diseases' prompt is answered as changing WHERE, WHEN and HOW MUCH existing diseases occur, with the emergence of genuinely new diseases flagged as an open research question rather than asserted. (2) The CPR project answer gives the broad current sequence and India's emergency number 112, but states plainly that CPR is a practical skill that cannot be learnt from a written description, that guidelines are periodically revised, and that it must be learnt hands-on from a qualified instructor - which is what the book itself asks by suggesting a doctor demonstrate a mock drill. (3) The four Indian scientists in the reading project are given as starting points describing the FIELD each worked in, with the student told to verify and cite sources and to note disagreement between them, rather than being handed specific dates and claims to reproduce.. Questions are referenced from the NCERT textbook for identification.
