SELINA Solutions for Class 9 Biology Chapter 16 - Diseases: Cause And Control

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Chapter 16 - Diseases: Cause And Control Exercise Ex. 1

Solution A

1. (c) pandemic

2. (d) AIDS

3. (c) Anopheles mosquito

4. (d) Entamoeba

5. (d) Tuberculosis

6. (b) Acquired Immuno Deficiency Syndrome

Solution B.1

(a) F (False). Filariasis is transmitted by the Culex mosquito.

(b) T (True)

(c) F (False). BCG vaccine is used for tuberculosis.

(d) F (False). Louis Pasteur discovered a cure for rabies. 

(e) F (False). AIDS is caused by a virus.

(f) T (True)

(g) T (True)

(h) F (False). Chicken pox and hepatitis are viral diseases.

(i) T (True)

(j) F (False). AIDS is caused by HIV virus.

(k) T (True)

(l) F (False). Smallpox has been eradicated from India.

(m) F (False). The disease filariasis is caused by the filarial worm Wuchereria bancrofti.

Solution B.2

AIDS : Acquired Immunodeficiency Syndrome

Solution B.3

(a) Viruses

(b) BCG

(c) Lungs

(d) AIDS

(e) Vaccine

(f) Tsetse fly

(g) Virus

(h) Elephantiasis 

Solution C.1

Infection: The transmission of disease from one person to another is called infection.

Pathogen: Disease-causing micro-organism is called a pathogen.

Incubation period: Incubation period is the period between the entry of germs and the appearance of the first symptoms of the disease.

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

Solution C.2
The different ways in which infectious diseases can spread are as follows:

  • Direct contact: Person to person, animal to person and expected mother to child
  • Indirect contact: Doorknob, phone, etc.
  • Droplet transmission: Sneezing, coughing, etc.
  • Particle transmission: Air particles can transfer infectious diseases
  • Bites and Stings: Mosquitoes, lice, ticks, etc.
  • Food Contamination: Food, beverages, etc.
Solution C.3








Nutritional deficiency


Carcinogens like chemicals, tobacco smoking, pollution etc.


Solution C.4

Causative germ of AIDS:

HIV (Human immunodeficiency virus)

Transmission of AIDS:

(a) Sexual intercourse

(b) Mother to child transmission

(c) Contaminated blood transfusions

Solution D.1

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


(b) Incubation period: It is the period between the entry of germs and the appearance of the first symptoms of the disease. Example: Incubation period of pneumonia is 1-3 days.


(c) Chicken pox: It is a viral disease caused by the Herpes Varicella zoster virus. It spreads rapidly by close contact with an infected person. A live attenuated vaccine containing Varicella is administered to children of 12-18 months for active immunisation.


(d) Hepatitis A: It is a viral disease caused by Hepatitis A virus which results in inflammation of the liver. It has an incubation period of 14-45 days. It is mainly transmitted through contaminated food and water. 

Solution D.2


Causative agent




Protozoan, Plasmodium

Chills, high fever, profuse sweating, severe headache, nausea, vomiting, fatigue and body pain

Destruction of mosquitoes at all stages and avoid mosquito bites by using mosquito nets or repellents

Chicken pox

Virus, Varicella zoster

Highly irritating rashes near the chest and back, gradually spreading to the arms, legs, face and head

Active immunisation by administering live attenuated vaccine containing Varicella


Bacterium, Mycobacterium tuberculosis

Persistent cough, afternoon fever, bloody mucus, loss of weight, fatigue and chest pain

BCG vaccination and isolation of the patient