Study Materials

NCERT Solutions for Class 9th Science


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Chapter 13. Why Do We Fall ill

Additional -Questions 3




Why do we fall ill ?

Que. - What is antibiotic? How does it work?

Ans. – Antibiotic is a medicine which kills various Species of bacterias. It breaks the capsule of bacteria formed by them for protection. However its blocks the formation of capsule. Thus the bacteria die easily.

Que. – Write the different between Acute and chronic disease.

Ans. -

Acute disease.

(i) It has short incubation period.
(ii) It affects minimum organs of the body.
(iii) it does not affect the general health.
(iv) Examples: - common cold, fever etc.
Chronic disease.
(i) It has long incubation period.
(ii) It affects about the whole body.
(iii) It affects the general health.
(iv) Examples:- Tuberculosis, diabetes, etc.

Que. – How is antibiotic penicillin effective on bacteria?

Ans. – The penicillin is the most effective antibiotic on various species of bacteria those who are capsulated. It breaks the capsule of bacteria formed by them for protection.

Que. - Define health according to WHO?

Ans. – According to WHO, “Health is therefore a state of being well enough  to function well physically, mentally and socially”.

Que. – State any two conditions essential for good health.

Ans. – There are two conditions essential for good health.

(i) Good and balance diet.
(ii) Good economic conditions and physical environment.

QUES: Define infectious diseases.

ANS: Diseases where microbes are the immediate causes are called infectious diseases. Ex. – typhoid, tuberculosis, cholera etc.

QUES: Define non- infectious diseases.

ANS: There are also diseases that are not caused by infectious agents. Ex – diabetes, cancer, arthritis etc.

QUES: Name the bacterium which is responsible for peptic ulcer.

ANS: Helicobacter pylori.

Q- Name the some infectious agents.

ANS: Virus, bacteria, fungus, protozoa, worms.

QUES: Name the diseases caused by virus.

ANS: Diseases caused by viruses are the common cold, influenza, dengue fever and AIDS.

QUES: Name the diseases caused by bacteria.

ANS: Diseases like typhoid fever, cholera, tuberculosis and anthrax are caused by bacteria.

QUES: Name the diseases caused by fungi?

ANS: Most of the skin diseases are caused by fungi.

QUES: Name the causative organism of acne?

ANS: Staphylococci

QUES: Name the causative organism responsible for sleeping


ANS: Trypanosome.

QUES: Name the causative organism responsible for Kala-ajar.

ANS: Leis mania.

QUES: Define communicable diseases.

ANS: The diseases those spread very fast to each others. They communicate and so are also called communicable diseases. Ex – cholera, plague, swine flu etc.

QUES: Define non-communicable diseases.

ANS:The diseases those do not spread to each others. It means they do not communicate so such diseases are called non-communicable diseases. Ex. – typhoid, malaria, cancer etc.

QUES: Write the modes to spread the infections.

ANS:The diseases spread directly and indirectly from infected body to healthy body by air, soil, water.

Direct mode:
(i) Droplet: sneezing, coughing, talking.
(ii) Contact: sexual transmission.
(iii) Blood transmission: injection, blood transfusion.
Indirect mode:
(i) By the vector: Mosquitoes, flies, and other animals.
(ii) By infected air, water and food.
QUES: What is inflammation?

ANS: An active immune system recruits many cells to the affected tissue to kill off the disease-causing microbes. This recruitment process is called inflammation.  As a part of this process, there are local effects such as swelling and pain, and general effects such as fever.

QUES: On what factor does the severity of disease manifestations depend on?

ANS:The severity of disease manifestations depend on the number of microbes in the body.

QUES: What is immunization?

ANS:Immunization is a preventive system by various diseases, in which antigens are transmitted into body through injection in the form of vaccine to form antibodies against the micro-organisms of diseases.

QUES: Define sexual transmitted disease?

ANS:The diseases which occur due to sexual contact are known as sexual transmitted diseases. Ex – syphilis, AIDS, Gonorrhea.

QUES: On which types of microbes’ penicillin are effective?

ANS:The microbes having cell wall.

QUES: Why do antibiotics not effective on virus infection?

ANS:The life of viruses is different than bacteria. Many bacteria build cell wall, but all have not so, antibiotic blocks biochemical pathways of bacteria. But viruses do not use these pathways at all, and that is the reason why antibiotics do not work against viral infections.

QUES: In which disease do the symptoms of water phobia appear?


QUES: Write the mode of spreading AIDS.

A –

(i) By infected needle or syringe.
(ii) Pregnant mother to her baby.
(iii) By Sexual contact.
(iv) Blood transfusion
QUES: What disease may occur if any person is exposed by animal?


QUES: Write the name of vector of malaria.

ANS:Anopheles Female Mosquito.

QUES: Write the name of vector of cholera.

ANS:Doemstic flies.

QUES: On what Factor do the signs and symptoms of a disease depend ?

ANS: The signs and symptoms of a disease will thus depend on the tissue or organ which the microbe targets. 


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