NCERT Class 9 Science Notes & Solutions – Chapter 13 – Why Do We Fall Ill?

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Notes Why Do We Fall Ill?

Why Do We Fall Ill? | In-Text Questions & Answers | Exercises Questions & Answers | NCERT Class 9 Science Chapter 13

Q1. What does HEALTH mean to you?

Health is a state or condition of being well physically, mentally and socially to function effectively. Someone is doing his daily works without any difficulties and we may say that he is in good health. When all the students in a classroom become attentive, then generally we may term it as healthy attitude. Generally our aged grandparents can not do all works easily and we may say it as poor health. So basically health implies of being well enough for effective functioning.

Q2. Describe some personal and community related issues that affects health.

There are many personal and community related issues that affects health. Some are described in the following –

Physical Environment: Health implies of being well physically, mentally and socially. It can not be achieved fully by our own effort or will. The health of all organisms depend on their surroundings i.e. physical environment. For examples, health faces risk from flood, cyclone, earthquake etc.

Social Environment: Social environment is also an important deciding factor for our health as we live in society. The places where people live may be city, town or village and social environment of these places affects not only health but also physical environment.

Public Cleanliness: It is very important for individual health. If municipality or local governing body stops collection of garbage or cleaning the drains, what will happen? It will result huge accumulation of garbage and stagnant of drain-water in surrounding areas of our living. Undeniably this will increase the possibility of poor health.

Social Equality and Harmony: We eat food to be healthy and fit. This food is earned by doing work, so opportunity of job or doing work should be available. In addition, happiness is another factor to be healthy. As we all live in society, so we should live in harmony. If we quarrel with each other or mistreat each other or we are afraid of each other, we can not be healthy and happy. So social equality and harmony are also required for good health.

Q3. What makes differences between ‘HEALTHY’ and ‘DISEASE-FREE’?

Answer: Disease is subjected to an individual affair and sufferings whereas health is linked to not only individual but also society and community.

Basically disease is a specific and particular cause for being uncomfortable. In other words, disease may be termed as disturbed ease.

It is not always required to know exact the cause of the disease, such as if someone has loose motion, people generally term it as diarrhoea without knowing the absolute cause of loose motions. Someone is in poor health and it does not justify that he is suffering from certain disease. On the other side good health does not indicate of not being diseased. It matters person to person differently. Someone may be in poor health due disease. The disease may be simple or complex, identifiable or non-identifiable. Good health to a gymnast means his ability to stretch his body in desired direction. Same is applicable to dancers also. Having breathing capacity in lungs to control notes from the flute measures the healthiness of a musician. Actually it is necessary for real health to get chances or opportunity to explore or realize the unique potential in individual.

Q4. How do you know that there is a disease or why do we fall ill?

Our body has different type of tissues or organs for specialised functioning to keep us fit and healthy. Different systems in our body perform different functions such as the brain is thinking, the digestive system (stomach and intestines) is digesting food, the kidney is filtering urine, the heart is pumping, the musculoskeletal system (bones and muscles) is holding the body parts together and helping us to move.

What happens if any of our body system function improperly? It will bring some uncomfortable and worst changes in our body. Further we will notice some symptoms and signs of being uncomfortable i.e. disease.

Having fever, loose motions, headache, chest pain etc. are various types of symptoms. Generally symptoms can not lead fully to conclusive indication of a disease because a dozen of different diseases may show a common symptom. Doctor focuses on the signs on the basis of symptoms to find the accurate indication of the disease. In addition Doctor also suggests various diagnostic tests to pinpoint the accurate disease.

Q5. What is acute disease and how it affects our health?

The diseases which last only for short period of time are called acute diseases. Common cold is an example of acute disease as it lasts only for few days.

Any kind of disease affects proper functioning of our body system. It affects our health as it affects some organs and prevents them functioning properly. Thus it results poor health. Generally acute disease does not cause major effects on our health as it lasts only for few days. Acute disease also has no lasting effects on our health. For example, when you have a cold and cough, you will become well and fit within few days or a week.

Q6. What is chronic disease and how it affects our health?

The diseases which last for longer periods of time and has lasting effect on our health are the chronic diseases. Generally this type of ailment stays for long time, even as much as life. Asthma, thyroid, infection causing elephantiasis, tuberculosis etc. are example of chronic diseases.

We know that any disease prevents proper functioning of some organs in our body and causes poor health. Chronic disease has different, major and prolonged effects on our health as compared to acute disease. It has very drastic long-term effects such as losing weight, tiredness, inability to perform etc. subjected to the type of chronic disease.

Q7. What are the causes of diseases?

Any disease has some immediate and some contributory causes. Generally most of the diseases have multiple causes rather than single cause. Let assume that a baby is suffering from loose motions. The most probable immediate cause may be an infection from unclean drinking water. It may also be happened that the some other babies drink same water but do not get infected.

So we may say that the first baby is not healthy. Why? It may be malnourishment of the bay due to poor household. All these are secondary i.e. contributory causes. Another contributory cause is genetic differences of the bay which makes him vulnerable when exposed to pathogen. Another cause may be supplying of unclean drinking water due to lack of public services. So we may conclude that every disease has some immediate and contributory causes.

Q8. Define infectious and non-infectious diseases.

Generally we divide the immediate causes of diseases into two distinct types i.e.  A. infectious causes and B. non-infectious causes.

Diseases which are caused by the microbes or micro-organisms are known as infectious diseases. In this case, this infectious agent (microbes) can spread in the community and causes mass spread of the diseases. Chickenpox, diarrhoea, cholera etc. are examples of infectious diseases.

Non-infectious diseases are developed by mostly internal causes not by microbes. In this case, they can not spread in community. High blood pressure, sugar, cancers etc. caused by genetic reasons etc. are examples of non-infectious diseases.

Q9. Why do we need to classify infectious agents?

Answer: Like various groups of organisms, infectious microbes are found in a wide range of groups such as unicellular microbes or protozoans, viruses, bacteria, multicellular organisms like worms etc. Diseases caused by viruses are common cold, AIDS (HIV), influenza, dengue etc. and diseases caused by bacteria are cholera, typhoid, tuberculosis, anthrax etc. Diseases caused by protozoans are malaria, kala-azhar etc. Elephantiasis, intestinal worms etc. are caused by various worms. In conclusion, we see that different kinds of diseases are caused by different kinds of agents. So we need to classify agents causing various diseases to pinpoint the kind of treatment is required for a particular disease.

Q10. How does grouping of microbes help in treatment?

Various groups of microbes have different kinds of characteristics. Viruses, bacteria, fungi can multiply rapidly but worms can multiply very slowly. On the other side viruses can live in host cells but bacteria does not. In addition, we observe that taxonomically all bacteria are closely related to each other but viruses are not. Generally it implies that many important life processes are similar in groups of bacteria but different from viruses. So a drug that blocks life process of one type of bacteria, also can act other bacteria of similar characteristics. But same drug can not work against other microbes of different groups.

Let us study the case of antibiotics. Bacteria makes a cell-wall to protect themselves. So if we take antibiotic penicillin for a bacterial infection, it will block the process of building cell-wall by bacteria but it will no act on our body as human cells lack cell-wall. Penicillin also can act against other bacteria of similar characteristics. Thus many antibiotics work against many species of bacteria rather than acting against one.

Antibiotics can not act against viruses as it uses different pathways compared to bacteria. If we have a viral fever, antibiotics will not act but if we have viral fever with bacterial infection, antibiotics will work. But antibiotics will only work against bacterial infection not against viral infection.

Q11. Discuss different mediums through which diseases spread.

Answer: The infectious diseases can spread in a variety of ways. The microbes can easily move from an infected person to another non-infected person through these mediums. The common mediums through which microbes move are describes in the following –

Air: Diseases spread through air are common cold, tuberculosis, pneumonia etc. If an infected person sneezes or coughs, he throws out little droplets in the air. And these droplets contain infectious microbes. Now if someone sitting or standing close to the infected person, he can easily breathe in these droplets. Thus the microbes can easily enter into him and start a new infection. So it is advisable for an airborne diseased person to avoid crowded area to avoid mass spreading.

Water: Open defecation is highly unhygienic as it can easily mix with drinking water. If excreta from a person having infectious gut disease, mixes with drinking water in a locality, undoubtedly it increases possibility to infect other people living in that locality. Cholera is an example of waterborne disease. So safe drinking water is a must for good general health and open defecation should be avoided.

Why do we fall ill?
Common ways for transmission of diseases

Physical Contact and Vectors –

Physical Contact: These may be casual touches like hugging, handshakes, sports etc. or may be closest touches like sexual act and kissing. AIDS (HIV), Syphilis etc. are sexually transmitted disease. HIV can also be transmitted through blood to blood contact, even to infants during pregnancy of mother and through breast feeding.

Through Animals: Our world is full of biodiversity and transmission of the microbes through animals is inevitable and unavoidable. These intermediary animals that carry the microbes from the infected person to the other person are called vectors. Mosquitoes are commonest and well-known vector around us. Female mosquitoes require highly nutritious food in the form of blood for ability to lay mature eggs. Thus they feed many warm blooded animals including human and spread disease from one person to another person.

Q12. Is manifestation of disease organ specific or tissue specific?

Generally numbers of infectious microbes decide the severity of disease manifestations. If small number of microbes infect the body, then disease manifestations will be minor even unnoticed. But if large number of microbes attack the body, then the severity of disease manifestations will be major even life threatening.

Let discuss whether the manifestations of disease is organ specific or not. The airborne microbes can easily enter our body via our nose and the probable destination of the microbes is our lungs. Breathlessness and cough are general manifestations in lungs infection. Bacteria causing tuberculosis is an example of it.

Waterborne microbes enter our body through mouth and they can easily go to liver, intestines etc. Liver infection causes jaundice. Intestines infection may cause loose motions. Typhoid is also caused by bacterial infection in the gut lining.

All aforesaid disease manifestations are organ specific but disease like HIV (AIDS) that caused through sexual act spreads to all lymph nodes all over the body and attacks our immune system. The microbes of malaria that enters our body through mosquito bite go to the liver and later to red blood cells (RBC). The viruses of Japanese encephalitis also enter our body through mosquito bite and go to our brain. Headaches, vomiting, fits, unconsciousness etc. are general manifestations when microbes attack our brain. So signs and symptoms are to be observed to identify the affected tissue or organ to make ways for proper medication.

Inflammation –

Apart from these tissue specific effects, there are some common effects which depend on body’s immune system. When microbes enter into the body and attack some organs, our active immune system recruits and engage many cells to kill off the microbes. The way of engaging cells to finish microbes is called inflammation. The response by our immune system results local effects like swelling, pain etc. and general effects like fever. So immunity capacity is important to reduce the effects of disease.

The viruses of HIV (AIDS) damage functioning of the immune system of our body. Thus HIV affected people becomes vulnerable to other diseases and effects of these diseases grow from small to like threatening and ultimately results the death of HIV affected people. For example – due to unresponsive immune system in HIV affected people, a common cold may grow to pneumonia and minor gut infection may cause major diarrhoea with blood loss.

Q13. Discuss principles of treatment.

Answer:  What should we do when we have an infectious disease? Principles of treatment are actually the steps or advice to be taken and followed for curing of an infected person. Specifically we can divide it in two ways – A. First target is to reduce the effects of the disease,  B. Second target is to kill the infectious microbes of the disease.

We know that every disease causes some signs and symptoms due to inflammation. These may be local effects like swelling, pain etc. and general effects like fever, loose motions etc. Firstly we should start treatment to reduce the effects of the disease like bringing down the fever, reducing pain or loose motions. Sometimes sleeping or bed rest helps to conserve energy and makes infected person to feel better.

But treatment which reduces inflammation can not kill the infectious microbes. Therefore, we need to identify the disease accurately and start medication that will kill the microbes. We have learnt previously that infectious microbes may be unicellular or multi-cellular and they are grouped into viruses, bacteria, fungi and protozoa. As biochemical life processes of microbes of various groups are different with each other, so medications are different for each group of microbes.

Antibiotics –

So we require the drug which can block the biochemical pathways of the microbes that means stopping the respiration processes of the microbes and killing them. But the same drug should not affect us. Antibiotics fulfil these purposes of blocking the biochemical processes of the bacteria. There are also drugs available to kill the microbes belonging to protozoa group like malarial parasite.

Viruses unlike bacteria have few biochemical pathways of their own and use our machinery for their life process. It lowers the virus-specific targets that aim at. For this reason making anti-viral drug is tougher than making anti-bacterial drug. Despite all these limitations, effective anti-viral drugs are available presently. For example- HIV drug that keeps it’s infection under control and helps HIV infected people to live longer.

Q14. Why prevention of disease is better than cure?

Generally treatment has some limitations as follows-

  1. The infectious microbes attack some parts or organs in our body and damage their functioning. Sometimes medications fail to recover completely from that attack by the microbes.
  2. Treatment for any infection takes time and results complete rest for the infected person. This may happen despite being given proper medication.
  3. Some infectious diseases spread from the infected person to the healthy person and it can cause mass spread in the community.

Considering all these difficulties, of course it is better to prevent the disease than their cure.

Q15. Discuss various ways of prevention of diseases.

Answer:  Basically we can categorise various ways of prevention of diseases into two ways. These are  A. general ways, B. specific medication to a particular disease or vaccination.

A. General ways to prevent diseases:

  1. Avoiding overcrowded area by the infected person helps to reduce spreading of airborne diseases.
  2. Safe and clean drinking water help unquestionably to avoid spreading of water-borne diseases.
  3. Public hygiene i.e. clean and unpolluted environments and surroundings help to avoid vector-borne infections.
  4. Immunity: Does an infected person affect all around him? Obviously the answer is no but why? Because our immunity system plays an important role in fighting against microbes. Previously we learnt that immune system naturally recruits and engages cells in killing microbes. Sometimes immunity power of an individual can kill microbes resulting no manifestations of disease. Manifestations of disease will be seen if immune system fails to kill the infectious microbes. If numbers of microbes are less, then manifestations of disease will be minor. In addition proper and sufficient nourishment is required to keep immune system functioning properly.

B. Vaccination (specific way to prevent a particular disease):

Specific way to prevent a particular disease: Vaccination against a particular infection is a process in which immune system develops a memory of how to fight that infection. Vaccine of a particular disease puts something in our body that does not cause actual disease but mimics the microbes and helps to develop a memory of how to fight the actual disease. So our immune system automatically responds when actual microbes enter in our body. Nowadays children are vaccinated against many diseases like polio, hepatitis A, measles, diphtheria, tetanus, whooping cough etc.

Q16. What do you mean by immunisation?

Our immune system gets activated as soon as infectious microbes enter our body. It engages cells to kill off the microbes and develops a memory for that particular infection. So the next time when that particular or similar type infection happens, our immune system faces it with even greater strength. And it is the basic principle of immunisation. So immunisation actually means that having the disease once is a way of developing a memory to prevent the same disease again. It is observed especially that the people who once suffered from chickenpox, naturally owns the ability to prevent subsequent attack of chicken pox.

Q17. What are five ‘F’s? What preventive actions should be taken in case of five ‘F’s?

Answer: Fluids, Fingers, Flies, Fields and Floods are five ‘F’s. Generally we can prevent spread of disease by taking sanitary and hygienic steps as detailed below in case of aforesaid five ‘F’s.

A. Sanitation- We should treat water properly and store safely.
B. Hygiene- Water source should be protected by avoiding open defecation, chemical contamination etc.

A. Sanitation- In general we should wash hands with soap after defecation and similar works.
B. Hygiene- Specifically we should clean hands before meal and cooking.

A. Sanitation- We should not keep food open and uncovered.
B. Hygiene- Generally we can take steps to control flies like spraying insecticides, keeping surroundings clean etc.

A. Sanitation- Undoubtedly we should avoid open defecation.
B. Hygiene- We should clean all vegetables and fruits properly.

A. Sanitation- We should treat water properly for drinking. At the present time local governing body takes various steps for treatment of water in urban as well as rural areas.
B. Hygiene- Action should also be taken for proper drainage system to avoid flooding and accumulation of water.

In-Text Questions & Answers | NCERT Class 9 Science Chapter 13 | Why do we fall ill?

In-Text Questions & Answers | NCERT Class 9 Science Chapter 13 | Why do we fall ill? | Page No. 178 

1.State any two conditions essential for good health.

Good health is a state or condition of being well physically & free from any illness. A man in good health can do his daily works without any difficulties. Good health requires many condition. Two of them are –
a. Good & healthy social environment,
b. Balanced & nourishing food.

2. State any conditions essential for being free of disease.

Two conditions for being free of disease are –
a. Good & healthy social environment with public cleanliness.
b. Consumption of balanced & nutritious food.

3. Are the answers to the above questions (1 and 2) necessarily the same or different? Why?

The answers from both aforesaid questions are partially same & partially different. They are same to some extent because if we maintain the conditions are essential for good health, then naturally we can minimise the chances of getting diseases. On the other hand, they are partially different because good health is a state or condition of being well physically, mentally and socially to function effectively and disease free means not suffering from any disease. 

In-Text Questions & Answers | NCERT Class 9 Science Chapter 13 | Why do we fall ill? | Page No. 180 

1. List any three reasons why you would think that you are sick & ought to see a doctor. If only one of these symptoms were present, would you still go to doctor? Why or why not?

The three reasons are ⇒
a. Cold, cough & fever.
b. Headache.
c. Loose motion.
Shall I visit doctor depends on the persistence of the symptoms. If any symptom persists more than 2 – 3 days, then we should visit a doctor. The doctor will investigate further for proper treatment. Generally symptoms like headache & cold do not have much effect on our daily life routine. So it does not require visit to doctor in general.

2. In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?
a. if you get jaundice.
b. if you get lice.
c. if you get acne.

The long-term effects of jaundice on health are likely to be most unpleasant. Because ⇒
a. Lice & acne are acute problems of health. On the other hand, jaundice is a chronic disease.
b. Lice & acne can be cured in a short period of time whereas jaundice takes long time to be completely cured.
c. In addition, jaundice heavily affects the whole body, especially liver. 

In-Text Questions & Answers | NCERT Class 9 Science Chapter 13 | Why do we fall ill? | Page No. 186 

1. Why are we normally advised to take bland and nourishing food when we are sick?

Our immune system needs sufficient nourishment for better functioning which is basically supplied by nourishing food. The bland & nourishing food fulfil the energy lost during wear & tear of the organ of a sick person. These foods are generally non-spicy. Also these foods are easy to digest. They do not release acids that interfere in the treatment. So we are generally asked to take bland & nourishing food during our sickness to improve our immune system & better digestion.

2. What are the different means by which infectious diseases are spread?

Write down the answer of Q11 in detail.

3. What precautions can you take in your school to reduce the incidence of infectious diseases?

You can take following precautions to reduce the incidence of infectious diseases ⇒
a. Drink safe & clean water.
b. Wash your hands before eating food.
c. Avoid over-crowded classes.
d. Do not eat food that is exposed to flies & mosquitoes.
e. Use clean toilets.
f. Use handkerchief during sneezing & coughing.
g. Vaccinate yourself before infection affects.
h. Stay at home if your class friend is suffering from infectious disease.
i. Avoid water stagnation in your school premises as well as home to reduce mosquito breeding.

4. What is immunisation?

The process by which we are made resistant to diseases is called immunization. It helps us to become free from any illness. Generally immunization is done through vaccination. Vaccine stimulates the immune system of the body to protect against infection.

5. What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?

Available immunisation programmes ⇒
a) Polio drops against polio.
b) Vaccine against hepatitis.
c) BCG (Bacillus Calmette–Guérin) vaccine against tuberculosis.
d) Vaccine against chicken-pox.
e) Vaccine against measles.
f) DPT vaccine against diphtheria, whooping cough (pertussis) & tetanus.
Major health problems ⇒ These are chicken-pox, tuberculosis, hepatitis & tetanus.

Exercises Questions & Answers | NCERT Class 9 Science Chapter 13 | Why do we fall ill? | Page Nos. 187 - 188

1. How many times did you fall ill in the last one year? What were the illness?
a. Think of one change you could make in your habits in order to avoid any of/most of the above illness?
b. Think of one change you would wish for in your surroundings in order to avoid any of/most of the above illness?

Last year I suffered from malaria once & from cold & cough thrice. a ⇒ We need to avoid the company of the persons suffering from cold & cough. We also need to wear proper clothes during season change. In addition, we should use mosquito net to protect us from mosquito bite. b ⇒ We need to improve the sanitary condition in our surroundings. Also we should not allow stagnation of water in our house & surroundings to stop the breeding of mosquitoes.

2. A doctor / nurse / health-worker is exposed to more sick people than others in the community. Find out how she / he avoids getting sick herself/himself.

A doctor / nurse / health-worker work in hospital or health-care centre. So they expose themselves to more sick people than others in the community. Still they avoid getting sick because of ⇒
a. vaccination against various diseases.
b. regular sterilisation of medical equipment & sanitization of working area.
c. washing hands with soaps.
d. undergoing medical check-ups.

3. Conduct a survey in your neighbourhood to find out what three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.

Generally the three most common diseases are diarrhoea, tuberculosis & malaria. We need to take following steps to bring down the incidence of said diseases ⇒
a. Supply of safe drinking water.
b. Vaccination.
c. Prevention of water storage in surroundings.
d. Regular cleaning of drains & covering open drains.
e. Proper waste management.

4. A baby is not able to tell her / his caretakers that she / he is sick. What would help us to find out ⇒ a) that the baby is sick? b) what is the sickness?

a ⇒ The baby may cry continuously with restlessness. The baby may also have abnormal body temperature. In addition, the bay may not intake food properly. b ⇒ Firstly, we need to observe the symptoms & its severity to diagnose sickness properly. Symptoms may be organ-specific, tissue-specific etc. For example, yellowness of skin & eyes indicates the jaundice.

5. Under which of the following conditions is a person most likely to fall sick?
(a) when she is recovering from malaria.
(b) when she has recovered from malaria & is taking care of some one suffering from chicken pox.
(c) when she is on a four-day fast after recovering from malaria & is taking care of someone suffering from measles.

Obviously the answer is c. Because fasting blocks sufficient nourishment. Due to fasting, health of the person will deteriorate & will become poor. So the person will not be able to take care of the sick person. In addition, chicken-pox is infectious disease. It also spread easily from one to another. So the person may get infection from the sick person suffering from chicken-pox.

6. Under which of the following conditions are you most likely to fall sick?
(a) when you are taking examinations.
(b) when you have travelled by bus & train for two days.
(c) when your friend is suffering from measles.

Of course the answer is c. Because measles is infectious viral disease. It also spread easily from one to another & causes fever & red rashes all over the body. So the person may get infection from his friend suffering from measles.

Why do we fall ill? – To Be Continued – Why do we fall ill?