CBSE Class 9 Biology Why Do We Fall Ill Notes

Download CBSE Class 9 Biology Why Do We Fall Ill Notes in PDF format. All Revision notes for Class 9 Biology have been designed as per the latest syllabus and updated chapters given in your textbook for Biology in Standard 9. Our teachers have designed these concept notes for the benefit of Grade 9 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 9 Biology for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 9 Biology given our website

Why Do We Fall Ill Class 9 Biology Revision Notes

Class 9 Biology students should refer to the following concepts and notes for Why Do We Fall Ill in standard 9. These exam notes for Grade 9 Biology will be very useful for upcoming class tests and examinations and help you to score good marks

Why Do We Fall Ill Notes Class 9 Biology

CBSE Class 9 Biology Why Do We Fall ill Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

Class IX: Biology

Chapter: Why do we fall ill

Chapter Notes

Key learnings:

1) Our body’s well-being is dependent on the proper functioning of its cells and tissues.

2) All our body parts and activities are greatly interconnected. Hence dysfunction of any body part will affect the entire body.

3) When we are healthy, we are able to perform our physical, mental and social functions well.

4) Our physical and social environment plays an important role in maintaining good health.

5) In addition to personal hygiene, public cleanliness should also be maintained for ensuring that we remain healthy.

6) Many other factors like financial conditions, availability of nutritious food and social equality also influence the health of an individual.

7) A person suffering from a disease is in a state of discomfort.

8) Being in poor health is different from being diseased.

9) Symptoms and signs of the disease appear as a result of dysfunction of the affected body parts. These help to identify the disease that a person is suffering from.

10) Depending on their duration, diseases may be classified as acute or chronic.

11) Acute diseases last for a short time and do not cause major health effects. E.g. Common cold. On the other hand chronic diseases persist for a long time and hence cause prolonged ill health. E.g. TB of lungs. D

12) Causes of diseases may be immediate (first level cause) or contributory. For e.g. – The immediate cause of a person suffering from diarrhoea is the causative agent. The contributory causes could be i) lack of good nourishment or genetic difference (second level cause), ii) poverty or lack of public services (third level cause)

13) Diseases may be infectious or non-infectious. Infectious diseases are caused by microbes or other infectious agents (e.g. Malaria) whereas non-infectious diseases have internal, non-infectious causes (e.g. High blood pressure).

14) The infectious agents may be viruses


15) The type of treatment of a disease depends on the category of the infectious agent.

16) Organisms belonging to one category will share several important life processes, which will be different from those of organisms belonging to other categories.

17) Drugs working by interfering with life processes of one category of organisms will not be effective against members of another category. E.g. Antibiotics act against bacteria, but not viruses, since viruses do not share bacterial pathways.

18) Penicillin interferes with bacterial cell wall production, thus killing the bacteria. Due to lack of cell walls, penicillin does not affect human cells.

19) Many infectious diseases are called ‘communicable diseases’ since they can spread from one person to another.

20) Communicable diseases can spread through air, water, food, sexual contact or vectors.

21) The droplets released during coughing or sneezing of an infected person causes the spread of air-borne diseases like common cold, pneumonia, tuberculosis etc.

22) Air-borne diseases spread quickly in overcrowded and poorly ventilated living conditions.

23) Water-borne diseases like cholera spread when drinking water gets contaminated with the infectious agents.

24) Sexual contact causes the spread of diseases like AIDS and syphilis from the infected person to a healthy one. AIDS virus can also spread through blood transfusions, use of infected needles or during pregnancy and breast-feeding by an infected mother.

25) Vectors are intermediate animals causing the spread of disease causing agents from an infected person to a healthy person. For example – Female mosquitoes transmit many diseases like malaria when they feed on the blood of animals and humans.

26) On entering the body, the infectious agents reach their specific target organs. In certain cases the target organ is related to their point of entry. For e.g. – Typhoid causing bacteria enter through mouth and reside in gut lining.

27) In other instances, the target organ of the microbe has no relation to their point of entry. For e.g. HIV enters through the sexual organs but spreads to all the lymph nodes.

28) The symptoms of a disease depend on the target organ infected by the microbe. For e.g. cough and breathing problems are seen when lungs are infected. So based on the signs and symptoms of a disease, we can get an idea of the target organ of the microbe.

29) During infection, the body’s activated immune system sends specialized cells to destroy the microbes, causing inflammation, with associated local effects.

30) The AIDS causing virus destroys the functioning of the immune system, due to which the body becomes unable to fight even minor infections. Ultimately the patient succumbs to such infections.

31) The severity of a disease is directly proportional to the number of infectious agents present in body.

32) An infectious disease can be treated in 2 ways:

i) Reduce the symptoms of the disease by providing treatment

ii) Kill the infectious agent causing the disease.

33) Medicines used in killing an infectious agent aim to disrupt some pathway of a vital life function peculiar to that group of organisms. These pathways are not present in other microbial groups or in humans.

34) On entering human cells, viruses use our cellular machinery for carrying out all their life processes. There are very few virus-specific biochemical pathways that can be targeted to produce anti-viral drugs.

35) The approach of treatment of an infectious disease has three drawbacks:

i) Recovery of the patient may not be complete in certain case

ii) Treatment requires time; hence the patient suffers from the disease and may be bedridden.

iii) The patient serves as the source of spread of infection to others.

36) It is desirable to prevent a disease than to treat it completely.

37) There are general and specific ways of preventing diseases.

38) Infectious diseases can be generally prevented by public health hygiene methods, which aim to reduce exposure to infectious microbes. Public hygiene measures include providing safe drinking water, clean environments and adequately spacious conditions for living.

39) Another general method of preventing infectious diseases requires the availability of sufficient and balanced diet for the proper functioning of the immune system. The immune system ensures that we do not develop a disease each time we are exposed to an infectious agent, by destroying the agent before it multiplies greatly.

40) During smallpox epidemics, it was noted that people who survived after suffering form smallpox, did not get infected with it again. Such observations led to the birth of immunization, which is a specific method of preventing infectious diseases.

41) The principle of immunization is based on the memory of the immune system on encountering an infectious agent. On subsequent encounters with the same or related microbe, the response of the immune system is multiplied greatly, leading to quick elimination of the infection.

42) During immunization, a vaccine (containing weakened or killed pathogen or a specific part of the pathogen) is introduced into the body to fool the immune system into remembering a particular infection. Hence the body does not suffer even on further exposures to that pathogen or its close relatives.

43) Nowadays, vaccines preventing many infectious diseases like tetanus, polio and measles are used extensively especially in child health immunization programmes.

44) Everyone in the community should have access to public hygiene and immunization for effective prevention of infectious diseases.

1) Health – A state of being well enough to function well physically, mentally and socially.

2) Disease - Lack of a feeling of ease due to impairment of health or a condition of abnormal functioning.

3) Acute disease – Disease lasting for a short period of time.

4) Chronic disease – Disease lasting for a long time, even as much as a lifetime.

5) Vectors – The intermediate animals causing the spread of infecting agents from a sick person to another potential host.

6) Infectious diseases – Disease where microbes are the immediate causes.

7) Communicable disease - A disease capable of being transmitted from an infected person to a healthy person.

8) Immediate cause of disease - The cause which immediately kindles a disease into action, when there occurs a predisposition towards it.

9) Contributary cause of disease – A cause or condition whose presence makes it more probable that a particular disorder will occur, but that cause is neither necessary nor sufficient for the occurrence of the disease.

10) Antibiotics - A substance produced by bacteria or fungi that destroys or prevents the growth of bacteria and other microorganisms.

11) Immunisation - The process of inducing immunity by administering a vaccine to allow the immune system to prevent infection or illness when it subsequently encounters the infectious agent.

12) Vaccine – A preparation of a weakened or killed pathogen or of a portion of the pathogen's structure that upon administration stimulates the immune system to fight against the pathogen but is incapable of causing severe infection.

13) Pathogen - Any disease-producing agent such as a virus or bacterium or other microorganism.

CBSE Class 9 Biology Why Do We Fall ill Notes

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