Why do children and elderly people fall ill more often?

Children have developing immune systems, and elderly people often have weakened immune systems due to age. Both groups are more vulnerable to infections and diseases due to their body’s reduced ability to fight off pathogens.

How does the environment influence our health?

The environment plays a significant role in health. Exposure to pollutants, toxins, unclean water, and poor sanitation can lead to illness. Clean air, water, and sanitary conditions are essential for preventing diseases.

What is immunity, and how does it protect us from illness?

Immunity is the body's defense mechanism against harmful pathogens. It involves the immune system identifying and neutralizing foreign invaders. A strong immune system helps prevent infections and keeps us healthy.

Can mental health affect physical health and illness?

Yes, poor mental health can weaken the immune system, increase stress levels, and negatively affect physical health, making the body more prone to illnesses and slower to recover from them.

CBSE Notes for Class 9 Science – Why do we fall ill?

S.No.	Disease free	Healthy
1.	One who is not suffering from any disease or derangement of the functioning of the body.	It is a state of physical, mental and social well being.
2.	It refers to the individual	It refers not only to the individual but also its surroundings.
3.	A disease free individual may have good health or poor health	A healthy individual is one who is able to perform normally under a given situation.

S.No.	Acute Disease	Chronic Disease
1.	Duration :- It is of shorter duration.	It is a longer duration disease.
2.	Persons :- Every person suffers from an acute disease at one time or the other.	Only some persons suffer from chronic diseases
3.	Recovery :- The recovery is generally complete after the treatment.	The recovery is seldom complete even after treatment.
4.	Loss :- Interruption of work and loss of efficiency are of short duration. Example :- Diarrhea, Typhoid.	Interruption of work and loss of efficiency are prolonged. Example :- Tuberculosis, Diabetes.

Causes (factors)	Diseases
Bacteria	Cholera, typhoid, diarrhea, pneumonia, tuberculosis, tetanus, diphtheria, leprosy, plague, pertussis or whooping cough, anthrax etc.
Virus	AIDS, rabies, diarrhea, hepatitis, polio, influenza, measles, mumps, smallpox, dengue, yellow fever, encephalitis, herpes, common cold, chicken pox etc.
Fungi	Madura foot, skin diseases, food poisoning etc.
Protozoans	Malaria, diarrhea, amoebic dysentery, sleeping sickness, kala-azar, giardiasis etc.
Worms	Filariasis (elephantiasis)

Medium for spread of the disease	Processes of spread of the disease	Name of diseases that can be spread this way
Air (Airborne Diseases)	Sneezing and coughing of an infected person causes tiny droplets of liquid containing bacteria/viruses to come out (droplet infection).	Common cold, Pneumonia, Tuberculosis, Influenza, Measles.
Food and Water borne Diseases	Food is contaminated by pathogens when patients do not have clean habits or flies that feed on sewage sit on food. Pathogens can get into water bodies when rainwater carries excreta/sewage into them.	Cholera, Typhoid, Hepatitis.
Through contact	When skin comes in contact with an infected person. By touching things like clothes, bedsheets etc. used by an infected person.	Scabies, Herpes, Ringworm, Conjunctivitis
Through body fluids	By sexual contact (STD) · Through Blood, semen or mother’s milk.	AIDS, Syphilis, Hepatitis B.
Through vectors	An animal that spreads disease is a vector. e.g. Mosquitoes, flies, cockroaches, rats.	Malaria, Typhoid, Kala-azar

Entry of microbes	Organ/tissue likely to be targeted by the microorganism	Examples of Diseases
Through eye	Eyes	Conjunctivitis
Through nose	Upper respiratory tract, lungs	Common cold, Tuberculosis
Through mouth	Intestine, Liver	Cholera,Typhoid Hepatitis
Through Blood	Brain, Liver/RBC's	Japanese Encephalitis Malaria

Frequently Asked Questions

Why do children and elderly people fall ill more often?

How does the environment influence our health?

What is immunity, and how does it protect us from illness?

Can mental health affect physical health and illness?

Join ALLEN!

CBSE Notes Class 9 Science - Why do we fall ill?

1.0Basic Conditions for Good Health

Differences Between Disease Free and Healthy

Disease

2.0Types of Disease - on the basis of duration

3.0Types of diseases

Infectious diseases

Common Effect of Infectious Disease

4.0Principles of Treatment

Symptom Directed Treatment

Limitations to Principles of Treatment of Infectious Disease

Prevention of Infectious diseases

General Methods

Specific Methods

Table of Contents

Frequently Asked Questions

Why do children and elderly people fall ill more often?

How does the environment influence our health?

What is immunity, and how does it protect us from illness?

Can mental health affect physical health and illness?

Join ALLEN!

CBSE Notes Class 9 Science - Why do we fall ill?

1.0Basic Conditions for Good Health

Differences Between Disease Free and Healthy

Disease

2.0Types of Disease - on the basis of duration

3.0Types of diseases

Infectious diseases

Common Effect of Infectious Disease

4.0Principles of Treatment

Symptom Directed Treatment

Limitations to Principles of Treatment of Infectious Disease

Prevention of Infectious diseases

General Methods

Specific Methods

Table of Contents