NCERT Class-9 Science Solutions: Chapter 13-Why Do We Fall Ill Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

Glide to success with Doorsteptutor material for CBSE/Class-9 : get questions, notes, tests, video lectures and more- for all subjects of CBSE/Class-9.

Question 35:

Why do some children fall ill more frequently than others living in the same locality?


Children fall ill more frequently due to

  1. Poor personal hygiene;
  2. Poor domestic hygiene;
  3. Unclean food;
  4. Lack of proper nutrition and balanced diet.

All these factors result i (i the weakening of the immune system, which makes these children more susceptible to disease.

Question 36:

Why are antibiotics not effective for viral disease?


Antibiotics generally block the biosynthetic pathways and they block these pathways of the microbes/bacteria. However, viruses have very few biochemical mechanisms of their own and hence are unaffected by antibiotics.

Question 37:

Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease. Explain.


Because of strong immune system our body is normally fighting off microbes. We have cells which are specialised to kill the pathogenic microbes. These cells are active when infecting microbes enter the body and if they are successful in removing the pathogen, we remain disease – free. So even if we are exposed to infectious microbes, it is not necessary that we suffer from diseases.

Image Antibiotics Work Against Viruses?

Question 38:

Give any four factors necessary for a healthy person.


For a healthy person it is necessary that

  1. The surrounding environment should be clean. Air and water borne diseases will not spread.
  2. Personal hygiene prevents infectious diseases.
  3. Proper, sufficient nourishment and food is necessary for good immune system of our body.
  4. Immunisation against severe diseases.

Question 39:

Why is AIDS considered to be a ‘Syndrome’ and not a disease?


Image the Symbol of HIV/AIDS

AIDS causing virus — HIV that comes into the body via, the sexual organs or any other means like blood transfusion will spread to lymph nodes all over the body. The virus damages the immune system of the body and due to this the body can no longer fight off many minor infections. Since AIDS result in collection of disease hence it is called a syndrome. Syndrome means collection of symptoms and signs of a disease. Instead, every small cold can become pneumonia, or minor gut infection can become severe diarrhea with blood loss. The effect of disease becomes very severe and complex, at times killing the person suffering from AIDS. Hence there is no specific disease symptoms for AIDS but it results in a complex diseases and symptoms. Therefore, it is known as a syndrome.

Developed by: