Science MCQ, Class 9th, Chapter-13, Why Do We Fall Ill?

NCERT based MCQ of Class 9th, Chapter-13, Why Do We Fall Ill? with brief explanation for competitive exams like TGT HTET, KVS PGT, TGT NVS, TGT EMRS, SSC and all other state competition exams.

Science MCQ, Class 9th, Chapter-13, Why Do We Fall Ill?
Along with MCQ, Chapter Key-Points for quick learning NCERT related facts are also discussed below.

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Summary of the Chapter-13-Why Do We Fall Ill?:

  • Health encompasses physical, mental, and social well-being.
  • An individual's health is influenced by their environment and economic situation.
  • Diseases are categorized as acute or chronic based on their duration.
  • Diseases can arise from infectious or non-infectious causes.
  • Infectious organisms can be microscopic and single-celled or multicellular.
  • The type of organism causing the disease determines the treatment approach.
  • Infectious diseases spread via air, water, direct contact, or through vectors.
  • Preventing disease is preferable to focusing solely on treatment.
  • Public hygiene measures that limit exposure to pathogens help prevent infectious diseases.
  • Immunization is another key strategy to prevent infectious diseases.
  • Successful prevention of infectious diseases in communities relies on widespread access to both sanitation and vaccines.

NCERT Based MCQ with Explanation:

1. What is the significance of health according to the chapter?

(a) Being disease-free

(b) Physical, mental, and social well-being

(c) Ability to recover from illness

(d) Resistance to all diseases

Explanation: Health is defined as the state of well-being, physically, mentally, and socially, and not just the absence of disease.


2. Which of the following is essential for individual health?

(a) High income

(b) Social equality and harmony

(c) Regular exercise

(d) All of the above

Explanation: According to the chapter, social conditions like equality and harmony are necessary for individual health.


3. How does the chapter define the difference between 'healthy' and 'disease-free'?

(a) They are the same

(b) Healthy means physically fit, disease-free means no infections

(c) Health is more comprehensive than being disease-free

(d) Disease-free means mentally sound, healthy means socially well

Explanation: Health involves physical, mental, and social well-being, whereas being disease-free only indicates the absence of disease.


4. Which of the following is a personal issue related to health?

(a) Access to clean drinking water

(b) Emotional stress

(c) Public sanitation

(d) Pollution

Explanation: Emotional stress is a personal factor that can affect health, while the others are community issues.


5. What is an example of a community issue that affects health?

(a) Bad diet

(b) Lack of physical activity

(c) Poor public sanitation

(d) Genetic predisposition

Explanation: Public cleanliness and sanitation affect the health of the entire community.


6. What is one cause of disease mentioned in the chapter?

(a) Lack of physical exercise

(b) Genetic abnormalities

(c) Overhydration

(d) Exposure to sunlight

Explanation: Some diseases, like cancer, can be caused by genetic factors as mentioned in the chapter.


7. What is an example of a chronic disease?

(a) Common cold

(b) Malaria

(c) Tuberculosis

(d) Diarrhea

Explanation: Tuberculosis is a chronic disease that persists for a long time, as stated in the chapter.


8. How are acute diseases defined in the chapter?

(a) Diseases that last for a long time

(b) Diseases that cause immediate death

(c) Diseases that last for a short period

(d) Diseases that are incurable

Explanation: Acute diseases, such as the common cold, are temporary and usually last for only a few days.


9. Which disease is not caused by infectious agents?

(a) Tuberculosis

(b) Malaria

(c) Diabetes

(d) Influenza

Explanation: Diabetes is a non-infectious disease that is caused by genetic and lifestyle factors.


10. What is the main function of antibiotics?

(a) Kill viruses

(b) Boost immune response

(c) Block biochemical pathways in bacteria

(d) Increase white blood cell count

Explanation: Antibiotics target specific processes in bacteria, like cell wall synthesis, making them ineffective against viruses.


11. Which of the following is a non-infectious cause of disease?

(a) Bacteria

(b) Virus

(c) Genetic mutation

(d) Protozoa

Explanation: Non-infectious diseases are caused by internal factors, such as genetic mutations, rather than external pathogens.


12. What does inflammation in the body signify?

(a) Healing of an injury

(b) Activation of the immune system

(c) Spread of infection

(d) Presence of chronic disease

Explanation: Inflammation occurs when the body’s immune system is fighting off infection or injury.


13. What is a vector?

(a) A type of virus

(b) An organism that transmits disease

(c) A type of bacteria

(d) A part of the immune system

Explanation: Vectors, like mosquitoes, carry and transmit infectious agents from one host to another.


14. Which of the following diseases is spread by vectors?

(a) Tuberculosis

(b) Malaria

(c) Cholera

(d) Common cold

Explanation: Malaria is transmitted through mosquitoes, which are the vectors.


15. Why don’t antibiotics work on viral infections?

(a) Viruses are too small for antibiotics to affect

(b) Viruses do not use biochemical pathways that antibiotics target

(c) Viruses are resistant to antibiotics

(d) Antibiotics are too weak to kill viruses

Explanation: Antibiotics target bacterial functions like cell wall production, which viruses do not possess.


16. What is the term used for diseases caused by infectious agents?

(a) Chronic diseases

(b) Non-communicable diseases

(c) Infectious diseases

(d) Genetic diseases

Explanation: Diseases caused by microbes that can spread from one person to another are called infectious diseases.


17. Which of the following is an example of a disease caused by a virus?

(a) Cholera

(b) Tuberculosis

(c) Malaria

(d) Influenza

Explanation: Influenza is caused by a virus, whereas cholera and tuberculosis are bacterial, and malaria is caused by protozoa.


18. What is a common way for waterborne diseases to spread?

(a) By breathing in contaminated air

(b) Through sneezing or coughing

(c) By consuming contaminated water

(d) Through physical contact

Explanation: Waterborne diseases spread when people consume water that is contaminated by pathogens, such as in the case of cholera.


19. How is malaria transmitted?

(a) Through contaminated food

(b) Through mosquitoes

(c) By direct physical contact

(d) Through contaminated water

Explanation: Malaria is transmitted through the bite of infected mosquitoes, making them vectors of the disease.


20. Which of the following is NOT a method of preventing infectious diseases?

(a) Immunization

(b) Good hygiene practices

(c) Avoiding antibiotics

(d) Access to clean drinking water

Explanation: While antibiotics treat bacterial infections, prevention involves practices like immunization and maintaining hygiene.


21. What is the role of vaccines in disease prevention?

(a) Cure diseases once they occur

(b) Strengthen muscles and bones

(c) Train the immune system to recognize and fight specific pathogens

(d) Replace antibiotics


22. Which of the following is NOT an infectious disease?

(a) AIDS

(b) Diabetes

(c) Typhoid

(d) Tuberculosis


23. What kind of diseases spread through the air?

(a) Waterborne diseases

(b) Vector-borne diseases

(c) Airborne diseases

(d) Genetic diseases


24. Which of the following conditions is most likely to spread infectious diseases?

(a) Crowded and poorly ventilated housing

(b) Open spaces with fresh air

(c) Low population density

(d) Regular hand hygiene


25. What is a symptom?

(a) A cause of disease

(b) An external agent that transmits disease

(c) A subjective feeling of discomfort

(d) A type of infection


26. What is a sign of disease?

(a) What a physician observes in a patient

(b) A specific symptom

(c) A person’s immune response to a pathogen

(d) A method of disease prevention


27. Which of the following is a key method for preventing the spread of vector-borne diseases?

(a) Maintaining a clean and dry environment

(b) Using antibiotics regularly

(c) Avoiding crowded places

(d) Eating more fruits and vegetables


28. Which of the following is a chronic disease?

(a) Common cold

(b) Influenza

(c) Hypertension

(d) Measles


29. What does the immune system do when faced with an infection?

(a) It ignores the infection

(b) It produces symptoms to signal disease

(c) It fights off the infection using specialized cells

(d) It prevents the body from functioning properly


30. Which of the following is NOT a principle of treatment for infectious diseases?

(a) Reducing symptoms like fever and pain

(b) Eliminating the cause of the infection

(c) Boosting the immune system

(d) Taking only rest without any medication

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