NCERT Exemplar Class 9 Science Solutions Chapter 13 Why do we fall ill?

NCERT Exemplar Class 9 Science Solutions Chapter 13-MCQ

Question:1

Which one of the following is not a viral disease?
(a) Dengue
(b) AIDS
(c) Typhoid
(d) Influenza
Answer: C
Infectious diseases are caused by infectious agents which are classified based on the typical characteristics of the organisms. These organisms that cause disease are found in viruses, bacteria, fungi, and single-celled and multi-cellular organisms.
Influenza, AIDS and Dengue are some examples of diseases caused by Viruses.
Typhoid fever is caused by bacteria called Salmonella typhi.
Hence, C option is the correct answer.

Question:2

Which one of the following is not a bacterial disease?
(a) Cholera
(b) Tuberculosis
(c) Anthrax
(d) Influenza
Answer: D
Infectious diseases are caused by infectious agents which are classified based on the common characteristics of the organisms. These organisms that cause disease are found in viruses, bacteria, fungi, and single-celled and multi-cellular organisms.
Cholera, Tuberculosis, and Anthrax are some examples of diseases caused by bacteria.
Influenza is caused by the infectious agent called Influenza Virus. It is transmitted by infected people when they sneeze or cough releasing the virus in the air, which in turn is inhaled by a non-infected person and causes the infection.
Hence, D is the correct answer.

Question:3

Which one of the following diseases is not transmitted by a mosquito?
(a) Brain fever
(b) Malaria
(c) Typhoid
(d) Dengue
Answer: C
Solution: Mosquitoes are the infecting agents that carry infections from sick people to a different host and are also termed as Vectors as they act as intermediaries. The female mosquitos require high nutrition to lay eggs that are acquired in the form of warm blood from animals and humans.
Brain Fever is also known as Encephalitis, which is transmitted by mosquitoes of Culex species.
Anopheles mosquitoes transmit malaria.
Aedes Mosquitoes transmit dengue fever.
Typhoid fever is caused by drinking contaminated water or eating contaminated food and can also be caused by the bacteria-contaminated toilet. The bacteria Salmonella typhi causes typhoid fever.

Question:4

Which one of the following diseases is not caused by bacteria?
(a) Typhoid
(b) Anthrax
(c) Tuberculosis
(d) Malaria
Answer: D
Solution: The bacteria Salmonella typhi causes Typhoid.
The bacteria Bacillus anthracis causes anthrax.
The bacterium Mycobacterium tuberculosis causes tuberculosis.
Malaria is caused by the protozoan microbes called Plasmodium vivax and transmitted by female Anopheles Mosquitoes.
Hence, D is the correct answer.

Question:5

Which one of the following diseases is caused by protozoans?
(a) Malaria
(b) Influenza
(c) AIDS
(d) Cholera
Answer: A
Solution: Influenza is caused by the infectious agent called Influenza Virus. It is transmitted by infected people when they sneeze or cough releasing the virus in the air, which in turn is inhaled by a non-infected person and causes the infection.
AIDS is caused by the Human Immunodeficiency Virus (HIV) and is transmitted by sexual contact, blood-to-blood contact (blood transfusion) with an infected person where the body fluids are getting exchanged with the non-infected person.
Cholera is caused by the bacterium Vibrio Cholerae and is transmitted by ingesting contaminated water or food.
Malaria is caused by the protozoan microbes called Plasmodium vivax and transmitted by female Anopheles Mosquitoes.
Hence, A is the correct answer.

Question:6

Which one of the following has a long-term effect on the health of an individual?
(a) Common cold
(b) Chickenpox
(c) Chewing tobacco
(d) Stress
Answer: Chewing tobacco is dangerous to health as it produces a long term effect.
Hence, C is the correct answer

Question:7

Which of the following can make you ill if you come in contact with an infected person?
(a) High blood pressure
(b) Genetic abnormalities
(c) Sneezing
(d) Blood cancer
Answer: C
Solution: Sneezing releases disease-causing microbes into the air from an infected person which is in turn inhaled by a healthy person causing illness. This causes communicable disease where the microbes initiate a new infection. A few examples of diseases caused by sneezing are tuberculosis and Pneumonia.
Hence, C is the correct answer.

Question:8

AIDS cannot be transmitted by
(a) sexual contact
(b) hugs
(c) breastfeeding
(d) blood transfusion
Answer: B
Solution: AIDS is caused by the Human Immunodeficiency Virus (HIV) and is transmitted by sexual contact, blood-to-blood contact (blood transfusion) with an infected person where the body fluids are getting exchanged with the non-infected person. A mother infected with AIDS can transmit the disease to her baby while breastfeeding.
Hugs or handshakes by or to an AIDS positive person does not transmit the virus.
Hence, B is the correct answer.

Question:9

Making anti-viral drugs is more difficult than making anti-bacterial medicines because
(a) viruses make use of host machinery
(b) viruses are on the borderline of living and non-living
(c) viruses have very few biochemical mechanisms of their own
(d) viruses have a protein coat
Answer: C
Solution: Anti-bacterial medicines block the bacteria from forming a cell wall. As there is no cell wall of a bacteria, it is unable to divide which leads to their termination. This functionality is provided by the antibiotics without affecting the cells of host’s body.
In case of a viral diseases, the virus uses the cells of infected person as the host and uses their biochemical mechanisms to sustain and divide as the viruses have very few biochemical mechanisms of their own. Anti-viral drugs are difficult to make as the drug needs to be extremely specific in destroying the viruses causing the disease without affecting or killing a significant number of the human body’s cells.
Hence, C is the correct answer

Question:10

Which one of the following causes kala-azar?
(a) Ascaris
(b) Trypanosoma
(c) Leishmania
(d) Bacteria

Answer: C
Solution: Ascaris causes Ascariasis in the small intestines. This is caused by a parasitic roundworm called Ascaris lumbricoides.Trypanosoma is a parasitic protozoan which causes Trypanosomiasis (sleeping sickness).Leishmania is the parasitic protozoan which causes the disease kala-azar. This disease is transmitted by the bite of infected female sand flies.


Hence, C is the correct answer.

Question:11

If you live in an overcrowded and poorly ventilated house, it is possible that you may suffer from which of the following diseases
(a) Cancer
(b) AIDS
(c) Airborne diseases
(d) Cholera
Answer: C
Solution: Air-borne diseases are caused by releasing disease-causing microbes into air. Sneezing or coughing releases disease-causing microbes into the air from an infected person which is in turn inhaled by a healthy person causing illness. This causes communicable disease where the microbes initiate a new infection. It is highly likely that the overcrowded and poorly ventilated house will lead to the infections from an infected person to other household members.
Hence, the correct answer is C.

Question:12

Which disease is not transmitted by mosquitoes?
(a) Dengue
(b) Malaria
(c) Brain fever or encephalitis
(d) Pneumonia
Answer: D
Solution: Mosquitoes are the infecting agents which carry infections from sick person to a different host and are also termed as Vectors as they act as intermediaries. The female mosquitos require high nutrition in order to lay eggs which is acquired in the form of warm blood from animals and humans.
Dengue fever is transmitted by Aedes Mosquitoes.
Malaria is transmitted by Anopheles Mosquitoes.
Brain Fever is also known as Encephalitis, which is transmitted by mosquitoes of Culex species.
Pneumonia is spread through air and is caused by bacteria, virus or fungi. This disease affects the lungs of infected person.
Hence, the correct answer is D.

Question:13

Which one of the following is not important for individual health?
(a) Living in clean space
(b) Good economic condition
(c) Social equality and harmony
(d) Living in a large and well-furnished house
Answer: D
Solution: Living in clean space is very much required to ensure that mosquitoes causing diseases such as Malaria and Dengue do not get a chance to breed and spread the infection. It is also necessary for avoiding contamination of the food and water which can cause diseases such as Typhoid.
Good economic conditions provide an individual to maintain a certain living standard which can lead to the eradication of diseases caused by poor hygiene and lack of resources.
Social equality and harmony provide an individual with the facilities and awareness to prevent a disease before it happens. It also provides a sense of mental stability which can reduce the stress in individuals.
Living in a large and well-furnished house is not important for individual health as it is not necessary that the individual maintain hygiene and follow all the instructions to prevent diseases.
Hence, the correct answer is D.

Question:14

Choose the wrong statement
(a) High blood pressure is caused by excessive weight and lack of exercise.
(b) Cancers can be caused by genetic abnormalities
(c) Peptic ulcers are caused by eating acidic food
(d) Acne is not caused by staphylococci
Answer: C
Solution: In many cases, high blood pressure is caused due to obesity and less physical activity of an individual. The excessive weight increases an individual’s blood pressure to rise. One of the reasons for an individual to have cancer is genetic abnormalities. Peptic ulcers are not caused by eating acidic food. Common cause for peptic ulcers is Helicobacter pylori bacteria which leads to stomach infection. Even smoking and excessive drinking of alcohol can lead to peptic ulcers.
Hence, C is the correct answer.

Question:15

We should not allow mosquitoes to breed in our surroundings because they
(a) multiply very fast and cause pollution
(b) are vectors for many diseases
(c) bite and cause skin diseases
(d) are not important insects
Answer: B
Solution: Mosquitoes are the infecting agents that carry infections from sick people to a different host and are also termed as Vectors as they act as intermediaries. The female mosquitos require high nutrition to lay eggs that are acquired in the form of warm blood from animals and humans. Thus, being the vectors for many diseases such as Malaria, Dengue fever and Encephalitis, mosquitoes should not be allowed to breed in our surroundings.
Hence, B is the correct answer.

Question:17

Viruses, which cause hepatitis, are transmitted through
(a) air
(b) water
(c) food
(d) personal contact
Answer: B
Hepatitis has five main types named A, B, C, D and E. Out of them, Hepatitis A is very common in India. The children in majority parts of the country get exposed to Hepatitis A virus through water and develops immunity. The most common cause of Hepatitis transmission is contaminated water.
Although, Hepatitis B is generally transmitted through the exchange of bodily fluids.
Hence, the correct answer is B.

Question:18

Vectors can be defined as
(a) animals carrying the infecting agents from sick person to another healthy person
(b) microorganisms which cause many diseases
(c) infected person
(d) diseased plants
Answer: A
Solution: The animals which carry infectious agents such as viruses, bacteria, protozoans etc. from an infected person to a healthy host are also termed as intermediaries or vectors. The most common example for Vectors is mosquitoes which causes many diseases such as Malaria, Dengue fever etc.
Hence, the correct answer is A.

NCERT Exemplar Class 9 Science Solutions Chapter 13-Short Answer

Question:19

Give two examples for each of the following
(a) Acute diseases
(b) Chronic diseases
(c) Infectious diseases
(d) Non-infectious diseases
Answer:

Two examples for each of the following are:

1. Acute diseases: The diseases which lasts for a certain (mostly short) period of time are termed as Acute diseases.

   Examples – Viral fever and Flu.
2. Chronic diseases: The diseases which last for a long span of time (in some cases for lifetime) are termed as Chronic diseases.

Examples – Elephantiasis and Tuberculosis.

3. Infectious diseases: The diseases caused by infectious agents such as viruses, bacteria, fungi, protozoans are termed as infectious diseases.

Examples – Chicken Pox and HIV/Aids.

4. Non-infectious diseases: The disease which cannot be transmitted via infecting agents are termed as Non-infectious diseases.

Examples – Cancer and Diabetes.

Question:20

Name two diseases caused by Protozoans. What are their causal organisms?
Answer:

Two diseases caused by Protozoans are:

1. kala-azar
2. Sleeping sickness (Trypanosomiasis)
3. Causal organisms for the above-mentioned diseases
4. kala-azar is caused by Leishmania
5. Sleeping sickness is caused by Trypanosoma

Question:21

Which bacterium causes peptic ulcers? Who discovered the above pathogen for the first time?
Answer:

The peptic ulcers are caused by Helicobacter pylori bacterium which leads to stomach infection.
This pathogen was discovered by two Australian researchers Barry J. Marshall and Robin Warren in the year 1982. Both of the researchers have been awarded with Nobel Prize in Medicine in the year 2005.

Question:23

Fill in the blanks
(a) Pneumonia is an example of ——— disease.
(b) Many skin diseases are caused by———.
(c) Antibiotics commonly block biochemical pathways important for the growth of ———.
(d) Living organisms carrying the infecting agents from one person to another is called ———.
Answer:

1. Pneumonia is an example of Bacterial disease.

2. Many skin diseases are caused by Fungi

3. Antibiotics commonly block biochemical pathways important for the growth of Bacteria.

4. Living organisms carrying the infecting agents from one person to another is called Vectors.

Question:24

Name the target organs for the following diseases
(a) Hepatitis targets———.
(b) Fits or unconsciousness targets ———.
(c) Pneumonia targets ———.
(d) Fungal disease targets ———.
Answer:

1. Hepatitis targets Liver.
2. Fits or unconsciousness targets Brain.
3. Pneumonia targets Lungs.
4. Fungal disease targets Skin.

Question:25

Who discovered ‘vaccine’ for the first time? Name two diseases which can be prevented by using vaccines.

Answer:

Vaccine was discovered by Edward Jenner in the year 1796. This vaccine was developed for smallpox and turned out to be the first successful vaccine in the world.
Two diseases which can be prevented by using vaccines:

1. Smallpox

2. Polio

Question:26

Fill in the blanks
(a) ——— disease continues for many days and causes——— on body.
(b) ———disease continues for a few days and causes no longer-term effect
on body.
(c) ——— is defined as physical, mental and social well-being and comfort.
(d) Common cold is——— disease.
(e) Many skin diseases are caused by———.
Answer:

1. Chronic disease continues for many days and causes long term effect on body

2. Acute disease continues for a few days and causes no longer-term effect on body.

3. Health is defined as physical, mental and social well-being and comfort.

4. Common cold is viral disease.

5. Many skin diseases are caused by fungi.

Question:27

Classify the following diseases as infectious or non-infectious.
(a) AIDS
(b) Tuberculosis
(c) Cholera
(d) High blood pressure
(e) Heart disease
(f) Pneumonia
(g) Cancer
Answer:

Question:28

Name any two groups of micro-organisms from which antibiotics could be extracted.
Answer:

Two groups of micro-organisms from which antibiotics could be extracted are:

1. Bacteria: Example for the same is Streptomyces species.
2. Fungi: Example for the same is Penicillium notatum.

Question:29

Name any three diseases transmitted through vectors
Answer:

The animals which carry infectious agents such as viruses, bacteria, protozoans etc. from an infected person to a healthy host are also termed as intermediaries or vectors. The most common example for Vectors is mosquitoes which cause many diseases such as Malaria, Dengue fever etc.

Three diseases transmitted through vectors are:

1. Brain Fever is also known as Encephalitis, which is transmitted by mosquitoes of Culex species.
2. Malaria is transmitted by Anopheles Mosquitoes.
3. Dengue fever is transmitted by Aedes Mosquitoes.

NCERT Exemplar Class 9 Science Solutions Chapter 13-Long Answer

Question:30

Explain giving reasons
(a) Balanced diet is necessary for maintaining healthy body.
(b) Health of an organism depends upon the surrounding environmental conditions.
(c) Our surrounding area should be free of stagnant water.
(d) Social harmony and good economic conditions are necessary for good health.
Answer:

1. An individual maintaining a balanced diet will in turn have a healthy body. The diet which we consume everyday provides our body with the fuel required to function and complete the daily physical and mental activities. A balanced diet should consist of an ample amount of proteins, minerals, vitamins, lipids and carbohydrates. An appropriate proportion of these biomolecules helps the body to have proper growth and leads to disease-free state.
2. The environmental conditions surrounding an organism plays a significant role in the organism’s health as poor hygiene conditions in the surrounding environment can lead to many diseases such as Malaria and Dengue fever. If the environment is contaminated, then the organism can develop severe diseases. An example to this is the harmful radiations and pollution which propagate a large number of diseases

3. It is very important to keep the surrounding area free from stagnant water because stagnant water becomes breeding grounds for many vectors such as Mosquitos and Swine, which transmits many diseases like Dengue and Malaria. The surroundings should always stay free from stagnant water to avoid an outbreak of these vector-based diseases.

4. Social harmony is necessary for good health as the individuals living in different communities should hold values of peace, admiration, generosity, respect and equity in the society to make the society’s and individual’s health better.

   Good economic conditions are a base for good health as these conditions equip an individual with good quality hygiene food and ability to deal with the expensive treatments required to restore good health.

Question:31

What is a disease? How many types of diseases have you studied? Give examples
Answer:

The disease is the cause for change in either the functioning or appearance of one or more systems of a body. These changes worsen the state of a healthy body and lead to malfunctioning of one or more than one organ.

The four types of diseases studied are mentioned below:

1. Acute diseases: The diseases which last for a certain (mostly short) period of time are termed as Acute diseases.
   Examples – Viral fever and Flu.

2. Chronic diseases: The diseases which last for a long span of time (in some cases for a lifetime) are termed as Chronic diseases.

   Examples – Elephantiasis and Tuberculosis.
3. Infectious diseases: The diseases caused by infectious agents such as viruses, bacteria, fungi, protozoans are termed as infectious diseases.
   Examples – Chicken Pox and HIV/Aids.

4. Non-infectious diseases: The disease which cannot be transmitted via infecting agents are termed as Non-infectious diseases.

   Examples – Cancer and Diabetes.

Question:32

What do you mean by disease symptoms? Explain giving two examples?
Answer:

Every disease showcases its signs and symptoms, these are generally termed as disease symptoms. Some symptoms can be common for various diseases; however, others are extremely specific to each disease. These symptoms help a doctor to identify the particular disease affecting the patient and take necessary actions (medication, procedures etc.)
Examples for disease symptoms:

1. COVID – 19 symptoms:
   1. Most Common Symptoms

      1. Fever

      2. Tiredness

      3. Dry Cough

         1. Shortness of breath

         2. Chest pain

   2. Less Common Symptoms:

      Dengue symptoms

      1. Vomiting

         Less Common Symptoms:

      2. Nause

      3. Headache

      4. Fever

      5. Rash

      6. Swollen gland

      7. Most Common Symptoms:

Question:33

Why is immune system essential for our health?
Answer:

The immune system has a significant role in protecting our body against germs, harmful substances and cell changes which lead to illness in an individual. The immune system consists of cells, organs and proteins.
The absence or poor immune system can leave an individual’s body unprotected against the harmful substances which enter inside or affects from outside onto our system.
The primary tasks that an immune system does for our health care:

1. Fight against diseases caused by viruses, fungi, parasite and bacterial.
2. Fight against diseased which cause cell changes in the body such as cancer cells.
3. Identifies and counterbalances threats in the environment

The immune system gets activated whenever our body comes into contact with harmful things and prevent it from damaging the body. Thus, immune system is essential for our health.

Question:34

What precautions will you take to justify “prevention is better than cure”.
Answer:

The term “prevention is better than cure” was coined around 1500 by a Dutch philosopher Desiderius Erasmus. This term has become one of the fundamental principles in the modern health care system.
The precautions we need to take in order to justify the term “prevention is better than cure” are:

1. A healthy and balanced diet to keep our immune system strong.
2. All the prescribed vaccinations should be taken within the specified time.
3. Awareness programs regarding common diseases and their prevention.
4. Daily exercise can strengthen the immune system.
5. Our environment should be kept clean and green by removing stagnant water and planting trees

6. Always keep your surroundings and body in good hygiene.

7. Pollution should be reduced in order to have a clean environment.

Question:35

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

Some children fall ill more frequently than others living in the same locality due to weak immune systems which can be because of the unbalanced diet or malnutrition. If a child has missed his/her vaccinations, then he is more prone to succumb to a disease. Other reasons for the above-mentioned condition can be unhygienic and congested living conditions and contaminated water and food.

Question:36

Why are antibiotics not effective for viral disease?
Answer:

Anti-bacterial/Antibiotic medicines block the bacteria from forming a cell wall. As there is no cell wall of a bacteria, it is unable to divide which leads to their termination. This functionality is provided by the antibiotics without affecting the cells of the host’s body. In the case of viral diseases, the virus uses the cells of an infected person as the host and uses their biochemical mechanisms to sustain and divide as the viruses have very few biochemical mechanisms of their own. And the viruses are not using these biochemical pathways so antibiotics have no effect on them as these medicines only work against the bacterial diseases.

Question:37

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

Answer:

The most recent example for the same can be seen from the pandemic of COVID-19. The effects of this virus got spread across the world over a significant population. Though being the same disease, it affected the population with symptomatic and asymptomatic conditions. An individual’s immune system counters the infectious microbe and kills the same by specialised cells. In case of strong immunity, the cells activate as the infectious microbe enters into the body and removes the same. This is why it does not necessarily mean developing a noticeable disease.

Question:38

Give any four factors necessary for a healthy person.
Answer:

Four factors necessary for a healthy person are:

1. A neat and clean environment: The surrounding environment must stay clean and green to prevent the diseases transmitted via air and water

2. A balanced diet and regular exercise: This will keep a person healthy and boost the immunity system

3. Personal hygiene: A healthy person should keep the surroundings as well as personal hygiene under check and take continuous necessary steps to maintain the same

4. Timely vaccination: To keep the body immune of existing viruses, a healthy person is required to get all the vaccinations done in a prescribed and timely manner.

Question:39

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

AIDS is caused by the Human Immunodeficiency Virus (HIV) and is transmitted by sexual contact, blood-to-blood contact (blood transfusion) with an infected person where the body fluids are getting exchanged with the non-infected person.
When an individual is HIV positive, the virus weakens and blocks our immune system which results in the body’s inability to fight against common infections such as cold or gut infection. Due to this inability, a minor infection of cold can turn into Pneumonia and gut infection can lead to diarrhoea resulting in blood loss.
AIDS does not show any specific symptoms but can turn minor diseases into major resulting in an individual’s demise. Therefore, due to the complexity of this disease and its symptoms which cannot be related to a single disease or identifiable pathogens, it is termed as Syndrome.