14 marksCuriosity Grade 8, Chapter 3, Section 3.4.1, pages 32-33
How do pathogens spread from one person to another? What is a vector?
Hint. Fig. 3.4 shows five routes.
How pathogens enter the body. Through the air we breathe, or by consuming contaminated food or water, among other routes.
The ways they travel between people (Fig. 3.4):
| Route | How it works | Example |
|---|
| Through air | An infected person coughs or sneezes | Cold, flu, measles, TB |
| Direct contact | Touching an infected person, e.g. shaking hands | Chickenpox |
| Indirect contact | Sharing personal items of an infected person | Cold and flu |
| Contaminated food or water | Drinking or eating what a pathogen has reached | Cholera, typhoid, hepatitis A |
| Insects | Carried by mosquitos and houseflies | Malaria, dengue |
Fig. 3.4 also shows a rabid animal infecting a healthy person — a bite as a route of transmission.
Vectors. Insects such as mosquitos and houseflies that spread pathogens are called vectors. The vector is not the cause of the disease — it is the carrier. Malaria is caused by a protozoan; the mosquito merely delivers it.
Why identifying the route matters. Prevention follows directly from it: masks and covering the mouth for airborne spread, boiled water for waterborne, mosquito nets for vector-borne. Get the route wrong and the precaution is useless.
✦ Answer: pathogens spread through the air (coughing, sneezing), by direct contact such as shaking hands, by indirect contact through shared personal items, through contaminated food and water, and by insects; insects such as mosquitos and houseflies that carry pathogens are called vectors.
24 marksCuriosity Grade 8, Chapter 3, Table 3.1, pages 33-34
From Table 3.1, list the diseases that spread through the air, with their causal agent, site of infection and main symptoms.
Hint. Four diseases, and only one of them is bacterial.
The air-spread group of Table 3.1.
| Disease | Causal agent | Site of infection | Symptoms |
|---|
| Common cold and influenza | Virus | Respiratory tract | Nasal congestion and discharge, sore throat, fever, cough, body ache |
| Chickenpox | Virus | Respiratory tract, skin | Mild fever, itchy skin, rashes, blisters |
| Measles | Virus | Skin, respiratory tract | Fever, sore throat, reddish rashes on the neck, ears and other parts of the skin |
| Tuberculosis (TB) | Bacteria | Lungs | Cough, fever, fatigue, loss of appetite, night sweats |
Preventive measures — note how they overlap, because the route is the same:
- Covering the mouth and nose — listed for all four
- Vaccination — for chickenpox, measles and TB
- Isolation of the patient — for chickenpox (complete isolation) and measles
- Washing hands frequently, not sharing personal items, wearing a mask — for cold and flu
- Avoiding close contact with TB-infected people, maintaining good hygiene
Two things worth extracting. Three of the four are viral, and the one bacterial disease — TB — is the one that settles in the lungs. And no vaccination is listed against the common cold, while the other three all have one.
✦ Answer: common cold and influenza (virus, respiratory tract), chickenpox (virus, respiratory tract and skin), measles (virus, skin and respiratory tract) and tuberculosis (bacteria, lungs) — all prevented chiefly by covering the mouth and nose, with vaccination available for chickenpox, measles and TB.
34 marksCuriosity Grade 8, Chapter 3, Table 3.1, page 34
From Table 3.1, list the diseases that spread through contaminated water and food, with their causal agent and site of infection. What single set of precautions prevents most of them?
Hint. Three of the four attack the same organ.
The water- and food-spread group of Table 3.1.
| Disease | Causal agent | Site of infection | Symptoms |
|---|
| Hepatitis A | Virus | Liver | Fatigue, fever, loss of appetite, nausea, vomiting, jaundice, pain in the upper right abdomen |
| Cholera | Bacteria | Intestine | Diarrhoea and dehydration |
| Typhoid | Bacteria | Intestine | Headache, abdominal discomfort, fever, diarrhoea |
| Ascariasis (roundworms) | Worms | Intestine | Worms in stool, loss of appetite, poor growth, diarrhoea, weight loss, anaemia |
The shared precautions. Because the route is the same, the same measures work against all of them:
- Boiled drinking water
- Properly cooked food
- Personal hygiene and good sanitary habits
- Vaccination — available for hepatitis A, cholera and typhoid, but not listed for ascariasis
Two observations. Three of the four settle in the intestine, which makes sense for pathogens swallowed with food or water; hepatitis A is the exception, reaching the liver. And ascariasis is caused by worms rather than a microorganism, which is why it has no vaccine in the table.
✦ Answer: hepatitis A (virus, liver), cholera (bacteria, intestine), typhoid (bacteria, intestine) and ascariasis (worms, intestine) — all prevented by boiled drinking water, properly cooked food and good personal hygiene and sanitation, with vaccination available for the first three.
43 marksCuriosity Grade 8, Chapter 3, Table 3.1, page 35
Which diseases in Table 3.1 are transmitted by insects? Give their causal agents and preventive measures, and note what is different about dengue's prevention.
Hint. The two causal agents are not the same kind of organism.
The insect-transmitted group of Table 3.1.
| Disease | Causal agent | Site of infection | Symptoms |
|---|
| Malaria | Protozoa | Skin, blood | High fever, profuse sweating, periodic chills |
| Dengue fever (break bone fever) | Virus | Skin, blood | Fever, headache, muscle and joint pain, nausea |
Shared preventive measures:
- Mosquito nets and repellents
- Wearing long-sleeved clothes
- Controlling mosquito breeding in and around your home
What is extra for dengue: avoiding areas with still water. Still water is where mosquitoes breed, so removing or avoiding it attacks the problem at its source rather than only shielding you from bites.
The important distinction. The mosquito is the vector, not the cause. Malaria is caused by a protozoan and dengue by a virus — two completely different kinds of pathogen carried by the same kind of insect. That is why the preventive measures are nearly identical even though the diseases are not.
Why 'break bone fever'. The name records dengue's severe muscle and joint pain.
✦ Answer: malaria (caused by protozoa) and dengue (caused by a virus), both carried by mosquitoes as vectors — prevented by mosquito nets, repellents, long-sleeved clothes and controlling breeding, with dengue additionally requiring avoiding areas with still water.
53 marksCuriosity Grade 8, Chapter 3, Section 3.4.1, page 35
List the simple precautions the chapter gives for preventing communicable diseases, and explain why staying home when unwell helps twice over.
Hint. The last item on the list does two jobs at once.
The chapter's list:
- Keeping ourselves and our surroundings clean
- Practising basic hygiene every day
- Washing hands with soap and water to remove pathogens
- Covering our mouth and nose while coughing or sneezing
- Wearing a mask in crowded places
- Avoid sharing personal items like towels and handkerchiefs
- Keeping our home, food and water clean
- Staying at home and resting when unwell
Why the last one counts twice. The chapter says it plainly: staying at home and resting helps the body recover and minimises spreading the disease to others. One action, two benefits — a personal one and a public one.
How the list maps onto the routes. Each precaution blocks a specific route of transmission: hand-washing and not sharing towels block contact; covering the mouth and masks block airborne spread; clean food and water block the food-and-water route; clean surroundings deny vectors their breeding places. Knowing the route tells you which precaution matters.
✦ Answer: cleanliness, daily hygiene, hand-washing with soap, covering mouth and nose, masks in crowds, not sharing personal items, clean home food and water, and resting at home when unwell — the last helping twice, since it both aids recovery and stops the disease spreading to others.
63 marksCuriosity Grade 8, Chapter 3, Section 3.4.1, page 35
Some infectious diseases are caused by worms. Where do they live, how do they harm us, and what is a parasite?
Hint. The chapter defines 'parasite' in a single line here.
Where they live. Some infectious diseases are caused by worms that live inside our bodies, especially in the digestive system.
How they harm us. They feed on nutrients — the nutrients meant for us. That explains the symptoms listed for ascariasis in Table 3.1: loss of appetite, poor growth, weight loss and anaemia, alongside worms in the stool and diarrhoea. A child with worms may be eating enough and still be undernourished, because the food is not reaching them.
What a parasite is. The chapter's definition: an organism that lives in or on another living being. These worms live as parasites.
How they spread. Through contaminated food, water, soil, or contact with infected people or animals — which is why the preventive measures for ascariasis are the water-and-food ones: boiled drinking water, properly cooked food, and good personal hygiene and sanitation.
A useful contrast. In Chapter 2 you met Rhizobium living inside root nodules and helping the plant — both organisms benefit. A parasite takes without giving, which is what distinguishes the two arrangements.
✦ Answer: worms live inside the body, especially the digestive system, and feed on our nutrients, causing loss of appetite, poor growth, weight loss and anaemia; a parasite is an organism that lives in or on another living being, and these worms spread through contaminated food, water, soil or contact.
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.
