Study the table and think about what simple steps can help prevent each disease. Table 3.1: Some common communicable diseases affecting humans (pages 33–35). Diseases Causal agent Site of infection Symptoms Preventive measures Diseases spread through the air Common cold and influenza Virus Res

Group the diseases by how they travel , and one set of steps prevents the whole group. Route Diseases Simple steps that stop them Through air Common cold and influenza, chickenpox, measles, tuberculosis Cover the mouth and nose while coughing or sneezing; wear a mask in crowded places; do not share personal items; isolate the patient; wash hands frequently; get vaccinated (chickenpox, measles, TB) Through contaminated water and food Hepatitis A, cholera, typhoid, ascariasis Drink boiled or safe water; eat properly cooked food; maintain personal hygiene and good sanitary habits; use a toilet; wash hands before eating; get vaccinated (hepatitis A, cholera, typhoid) Through insects (vectors) Malaria, dengue fever Use mosquito nets and repellents; wear long-sleeved clothes; control mosquito breeding in and around the home; avoid areas with still water Two steps appear against every group and are therefore the most valuable of all: Washing hands with soap and water — the notice board records that regular handwashing reduces infection by 50%. Keeping ourselves and our surroundings clean. Why it happens: a pathogen has to complete a journey — leave one body, survive outside, and enter another. Every preventive step above breaks that journey at one point: the mask blocks the exit, boiling kills the pathogen on the way, the net blocks the entry, and the vaccine makes the destination body useless to it.

NCERT Solutions for Class 8th Science Chapter 3 Activity 3.4: Let us find out — How are communicable diseases caused and spread? (2026-27)

Q1.

Check the information listed by referring to books, trusted websites, or asking your science teacher. Add any missing details.

Answer

Table 3.1 as printed is correct. Checked against the chapter itself, this is the verified table, with one useful column added — the route by which each disease travels, since that is what decides how to stop it.

Disease	Causal agent	Site of infection	Main symptoms	How it spreads (added)
Diseases spread through the air
Common cold and influenza	Virus	Respiratory tract	Nasal congestion and discharge, sore throat, fever, cough, body ache	Droplets from coughs and sneezes; sharing personal items
Chickenpox	Virus	Respiratory tract, skin	Mild fever, itchy skin, rashes, blisters	Droplets in air; contact with the blisters
Measles	Virus	Skin, respiratory tract	Fever, sore throat, reddish rashes on the neck, ears and other parts of the skin	Droplets in air
Tuberculosis (TB)	Bacteria	Lungs	Cough, fever, fatigue, loss of appetite, night sweats	Droplets from the cough of an infected person
Diseases spread through contaminated water and food
Hepatitis A	Virus	Liver	Fatigue, fever, loss of appetite, nausea, vomiting, jaundice, pain in the upper right abdomen	Drinking water or food contaminated with excreta
Cholera	Bacteria	Intestine	Diarrhoea and dehydration	Contaminated drinking water and food; flies
Typhoid	Bacteria	Intestine	Headache, abdominal discomfort, fever and diarrhoea	Contaminated drinking water and food
Ascariasis (roundworms)	Worms	Intestine	Worms in stool, loss of appetite, poor growth, diarrhoea, weight loss, anaemia	Contaminated food, water or soil
Diseases transmitted by insects
Malaria	Protozoa	Skin, blood	High fever, profuse sweating, periodic chills	Bite of a mosquito (vector)
Dengue fever (Break bone fever)	Virus	Skin, blood	Fever, headache, muscle and joint pain, nausea	Bite of a mosquito that breeds in clean, still water

Why the added column matters: the causal agent tells you what the disease is; the route tells you what to do. TB and measles are both stopped by covering the mouth; cholera and typhoid by boiling water; malaria and dengue by removing standing water — even though the pathogens are of four different kinds.

Note: the table lists protozoa, bacteria, viruses and worms. All four are pathogens, and the worms live as parasites — organisms that live in or on another living being.

Q2.

Study the table and think about what simple steps can help prevent each disease.

Table 3.1: Some common communicable diseases affecting humans (pages 33–35).

Diseases	Causal agent	Site of infection	Symptoms	Preventive measures
Diseases spread through the air
Common cold and influenza	Virus	Respiratory tract	Nasal congestion and discharge, sore throat, fever, cough, body ache	Washing hands frequently, not sharing personal items, covering the mouth and nose using a mask
Chickenpox	Virus	Respiratory tract, skin	Mild fever, itchy skin, rashes, blisters	Complete isolation of the patient, covering the mouth and nose, vaccination
Measles	Virus	Skin, respiratory tract	Fever, sore throat, and reddish rashes on the neck, ears and other parts of the skin	Isolation of the patient, covering the mouth and nose, maintaining good hygiene, vaccination
Tuberculosis (TB)	Bacteria	Lungs	Cough, fever, fatigue, loss of appetite, night sweats	Avoiding close contact with TB-infected people, covering the mouth and nose, maintaining good hygiene, getting vaccinated
Diseases spread through contaminated water and food
Hepatitis A	Virus	Liver	Fatigue, fever, loss of appetite, nausea, vomiting, jaundice, pain in the upper right abdomen	Drinking boiled water, vaccination
Cholera	Bacteria	Intestine	Diarrhoea and dehydration	Maintain personal hygiene and good sanitary habits, consumption of properly cooked food and boiled drinking water, vaccination
Typhoid	Bacteria	Intestine	Headache, abdominal discomfort, fever, and diarrhoea	Maintain personal hygiene and good sanitary habits, consumption of properly cooked food and boiled drinking water, vaccination
Ascariasis (roundworms)	Worms	Intestine	Worms in stool, loss of appetite, poor growth, diarrhoea, weight loss, anaemia	Maintain personal hygiene and good sanitary habits, consumption of properly cooked food and boiled drinking water
Diseases transmitted by insects
Malaria	Protozoa	Skin, blood	High fever, profuse sweating, periodic chills	Use of mosquito nets and repellents, wearing long-sleeved clothes, control of mosquito breeding in and around your home
Dengue fever (Break bone fever)	Virus	Skin, blood	Fever, headache, muscle and joint pain, nausea	Use of mosquito nets and repellents, wearing long-sleeved clothes, control of mosquito breeding in and around your home, avoiding areas with still water

Answer

Group the diseases by how they travel, and one set of steps prevents the whole group.

Route	Diseases	Simple steps that stop them
Through air	Common cold and influenza, chickenpox, measles, tuberculosis	Cover the mouth and nose while coughing or sneezing; wear a mask in crowded places; do not share personal items; isolate the patient; wash hands frequently; get vaccinated (chickenpox, measles, TB)
Through contaminated water and food	Hepatitis A, cholera, typhoid, ascariasis	Drink boiled or safe water; eat properly cooked food; maintain personal hygiene and good sanitary habits; use a toilet; wash hands before eating; get vaccinated (hepatitis A, cholera, typhoid)
Through insects (vectors)	Malaria, dengue fever	Use mosquito nets and repellents; wear long-sleeved clothes; control mosquito breeding in and around the home; avoid areas with still water

Two steps appear against every group and are therefore the most valuable of all:

Washing hands with soap and water — the notice board records that regular handwashing reduces infection by 50%.
Keeping ourselves and our surroundings clean.

Why it happens: a pathogen has to complete a journey — leave one body, survive outside, and enter another. Every preventive step above breaks that journey at one point: the mask blocks the exit, boiling kills the pathogen on the way, the net blocks the entry, and the vaccine makes the destination body useless to it.