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Chapter 16

Diseases: Cause and Control

Class 9 - Concise Biology Selina

Multiple Choice Type

Question 1

A disease widely spread worldwide is known as

  1. Endemic
  2. Epidemic
  3. Pandemic ✓
  4. Sporadic

Question 2

Use of disposable syringes for injecting medicines, etc. is specially advised to prevent

  1. Poliomyelitis
  2. Mumps
  3. Rabies
  4. AIDS ✓

Question 3

The vector that transmits the malarial pathogen is:

  1. Culex mosquito
  2. Housefly
  3. Anopheles mosquito ✓
  4. Entamoeba

Question 4

Amoebiasis is caused by the protozoan:

  1. Amoeba proteus
  2. Euglena
  3. Plasmodium
  4. Entamoeba ✓

Question 5

BCG vaccine provides immunity against:

  1. Tetanus
  2. Cholera
  3. AIDS
  4. Tuberculosis ✓

Question 6

The expanded form of AIDS is:

  1. Active Immunity Deficiency Syndrome
  2. Acquired Immuno Deficiency Syndrome ✓
  3. Acquired Immuno Deficiency Status
  4. Active Immuno Deficiency Syndrome

Very Short Answer Type

Question 1

Mention whether the following statements are true (T) or false (F).

(a) Filiariasis is transmitted by the housefly

(b) Malaria is caused by a protozoan

(c) BCG vaccine is used for chicken pox

(d) Louis Pasteur discovered a cure for malaria

(e) AIDS is caused by a bacterium

(f) HIV is a serious disease, usually fatal

(g) AIDS is not transmitted by contact with a patient’s clothes

(h) Chicken pox and hepatitis are bacterial diseases

(i) Goitre is endemic in sub-Himalayan regions of India

(j) AIDS is caused by a fungus

(k) Hay fever and asthma are allergies

(l) Smallpox still occurs in India

(m) The disease filiariasis is caused by the bite of female anopheles mosquito

Question 2

Write the full form of AIDS.


The full form of AIDS is — Acquired Immuno Deficiency Syndrome

Question 3

Name the following:

(a) Category of pathogen that causes diseases, like common cold and mumps ........

(b) The vaccine for preventing tuberculosis ........

(c) An organ usually affected by tuberculosis ........

(d) A disease that weakens body’s defense system against infections ........

(e) Germ or germ-substance introduced into the body to prevent occurrence of an infectious disease ........

(f) The vector responsible for transmission of sleeping sickness ........

(g) The microorganism that requires a host to produce ........

(h) The popular name of the disease filiariasis ........


(a) Viruses

(b) BCG

(c) Lungs

(d) AIDS

(e) Vaccine

(f) Tsetse fly

(g) Virus

(h) Elephantiasis

Short Answer Type

Question 1

Define the terms infection, pathogen, incubation period and allergen.


  1. Infection — The transmission of diseases from one person to another is called infection.

  2. Pathogen — A pathogen is a disease-causing micro-organism.

  3. Incubation period — Incubation period is the period between the entry of germs and appearance of the first symptoms of the disease. All infectious diseases have a certain incubation period.

  4. Allergen — An antigenic substance capable of producing immediate hypersensitivity allergy is called an allergen.

Question 2

What are the different ways in which infectious diseases can spread?


The different ways in which infectious diseases can spread are as follows:

  1. Direct contact — Person to person, animal to person and expected mother to child.
  2. Indirect contact — Doorknob, phone, etc.
  3. Droplet transmission — Sneezing, Coughing, etc.
  4. Particle transmission — Air particles can transfer infectious diseases
  5. Bites and Stings — Mosquitoes, lice, ticks, etc.
  6. Food Contamination — Food, beverages, etc.

Question 3

Name any four non-infectious diseases and their causes.


Non-infectious DiseasesCause of the Disease
Hay feverAllergy
CataractDegenerative (Ageing)
Beri-BeriNutritional deficiency
CancerCarcinogens like chemicals, tobacco smoking, pollution, etc.

Question 4

Name the causative germ of AIDS. How is this disease transmitted?


The causative of AIDS is HIV (Human Immunodeficiency Virus).

Transmission of AIDS:

  1. Sexual intercourse
  2. Contaminated blood transfusions
  3. Mother to child transmission
  4. Injection needles

Long Answer Type

Question 1

Write very briefly about the following:

(a) BCG

(b) Incubation period

(c) Chicken pox

(d) Hepatitis A


(a) BCG — BCG (Bacillus Calmette Guerin) is a vaccine which is effective against the bacterial disease tuberculosis(TB). It develops immunity to tuberculosis.

(b) Incubation period — Incubation period is the period between the entry of germs and appearance of the first symptoms of the disease. All infectious diseases have a certain incubation period.

(c) Chicken pox — The disease is a contagious disease occurring mainly in children, and is caused by Herpes Varicella zoster virus. The disease rapidly spreads through close contact with the person infected.

(d) Hepatitis A — It is caused by the Hepatitis A virus and is a viral disease that results in liver inflammation. It is transferred primarily through contaminated water and food.

Question 2

What are the causes and symptoms of malaria, chicken pox and tuberculosis? How can these diseases be prevented?


The causes, symptoms and preventive measures of these diseases are as given below:

  1. Malaria
    • Causes — Protozoan, Plasmodium.
    • Symptoms — Chills, high fever, profuse sweating, severe headache, nausea, vomiting, fatigue and body pain.
    • Preventive measures — Avoid mosquito bites using mosquito repellents and nets avoid being around stagnant water.
  2. Chicken Pox
    • Causes — Virus, Varicella zoster.
    • Symptoms — Rashes near the back and the chest eventually spreading to arms, face, legs and head.
    • Preventive measures — Active immunisation by administering live attenuated vaccine containing Varicella.
  3. Tuberculosis
    • Causes — Mycobacterium tuberculosis.
    • Symptoms — Persistent cough, afternoon fever, bloody mucus, loss of weight, fatigue and chest pain.
    • Preventive measures — BCG vaccination and isolation of the patient.