NCERT Solutions for Class 9 Science Chapter 13 - Why Do We Fall Ill?

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Answer:

Typhoid is a bacterial disease which is caused by Salmonella typhi. Dengue, AIDS and influenza are viral diseases.

Hence, the correct answer is option (c). 

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Influenza is a viral disease which is caused by orthomyxovirus, whereas cholera, tuberculosis and anthrax are bacterial diseases. 
 
Hence, the correct answer is option (d).

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Among the given options, typhoid is the only disease which is transmitted through contaminated food or water. The other three diseases, dengue, malaria and brain fever are transmitted through the vector (mosquito). 

Hence, the correct answer is option (c).
 

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Typhoid is caused by Salmonella typhi. Anthrax is caused by Bacillus anthracis and tuberculosis is caused by Mycobacterium. All three are bacteria. Malaria is caused by protozoa Plasmodium.

Hence, the correct answer is option (d).

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Influenza and AIDS are caused by viruses. Cholera is caused by bacteria. Malaria is caused by protozoans.

Hence, the correct answer is option (a).

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Tobacco contains nicotine that has a long-term effect on the health of an individual. Common cold, chicken pox and stress only have short-term effects on health.
Hence, the correct answer is option (c).

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Sneezing will make us ill if we come in contact with the infected person because sneezing would carry microbe-containing droplets that can cause infection in a healthy person. High blood pressure, genetic abnormalities and blood cancer are non-infectious diseases that are not spread from an infected person to a healthy person by any means.

Hence, the correct answer is option (c).

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AIDS(Acquired Immunodeficiency Syndrome) is spread through sexual contact, breastfeeding and blood transfusion. It is not spread through hugs, kisses, and eating food together.

Hence, the correct answer is option (b).

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Viruses are acellular in nature. They use host cell machinery after infection. They have very few biochemical mechanisms of their own that can be used as a target of anti-bacterial medicines.

Hence, the correct answer is option (c).

Disclaimer - Option (a) is also the correct answer as mentioned in the above explanation.

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Leishmania is the causative agent of kala-azar.

Hence, the correct answer is option (c).

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Living inside an overcrowded and poorly ventilated house can give rise to air-borne diseases because the air inside the house is not well circulated and if an infected person coughs or sneezes inside the house, the microbe bearing droplets will remain suspended in the air for hours.

Hence, the correct answer is option (c).

Answer:

Dengue, malaria and encephalitis are transmitted by vectors or mosquitoes. Only pneumonia is an air-borne disease.

Hence, the correct answer is option (d).

Answer:

Health is a condition of physical, mental and social well-being. A person must consider certain things to live a healthy life such as living in a clean space, having social equality and harmony and good economic condition to have nutritious food and treat certain diseases. However, living in a large and well-furnished house is not important to have a healthy life.

Hence, the correct answer is option (d).

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Acne is a type of skin condition where hair follicles clog due to the accumulation of oil and dirt. Acne is caused by the bacteria Staphylococcus aureus. 

Hence, the correct answer is option (d).

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Mosquitoes lay eggs in stagnant water. Female mosquitoes feed on human blood and spread many infectious diseases like malaria, dengue, brain fever etc. as a carrier. So, they act as a vector for many diseases.

Hence, the correct answer is option (b).

 

Answer:

Polio is a virus that enters our bodies through contaminated food or water. The virus affects the central nervous system of the infected person. To stop the disease children are given oral polio vaccines as it creates a memory within the immunity cells. Thus, protects the body from further infection.

Hence, the correct answer is option (c).

Answer:

Hepatitis is a virus that infects the human liver and causes jaundice. It is transmitted through contaminated water.

Hence, the correct answer is option (b).

Disclaimer - According to WHO, hepatitis virus is transmitted through faecal-oral route, that is, through ingestion of both contaminated food and water. Hence, both options (b) and (c) are correct. 

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A vector is an animal that carries the infecting agents from a diseased person to another healthy person. Like mosquito carries the protozoa of malaria from an infected person to a healthy person. So, a mosquito is a vector.

Hence, the correct answer is option (a).

Answer:

(a) Acute diseases - headache, heart attack.
(b) Chronic diseases - tuberculosis, diabetes.
(c) Infectious diseases - pneumonia, malaria.
(d) Non-infectious diseases - asthma, diabetes.

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Two protozoan diseases are malaria and kala-azar. Malaria is caused by Plasmodium and kala-azar is caused by Leishmania.

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Helicobacter pylori is the causative agent of peptic ulcers. 
Robin Warren (born 1937), a pathologist from Perth, Australia, saw these small curved bacteria in the lower part of the stomach in many patients. 

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Antibiotic is a type of chemical substance secreted by microorganisms that can inhibit or kill the growth of bacteria.
Examples of antibiotics are penicillin and streptomycin.

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(a) Pneumonia is an example of infectious disease.
(b) Many skin diseases are caused by fungi.
(c) Antibiotics commonly block biochemical pathways important for the growth of bacteria.
(d)  Living organisms carrying the infecting agents from one person to another are called vectors.

Answer:

(a) Hepatitis targets the liver.
(b) Fits or unconsciousness targets the brain.
(c) Pneumonia targets the lungs.
(d) Fungal disease targets the skin.

 

Answer:

Edward Jenner discovered 'vaccine' for the first time. He is also known as the father of vaccination.
Polio and tetanus can be prevented by using vaccines.

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(a) Chronic disease continues for many days and causes longterm effects on body.
(b) Acute disease continues for a few days and causes no longer term effect on body.
(c) Health is defined as physical, mental and social well-being and comfort.
(d) Common cold is viral disease.
(e) Many skin diseases are caused by fungi.

 

Answer:

Infectious diseases are those that transmit from an infected person to a healthy person through any object, medium or vector. AIDS (spread through sexual contact or infected body fluids), tuberculosis (spread through air), cholera (spread through contaminated food or water), pneumonia (spread through air) are infectious diseases.
Non-infectious diseases do not spread from an affected person to a non-affected person. High blood pressure, heart disease and cancer are non-infectious diseases.

Answer:

Antibiotic is a type of chemical substance secreted by microorganisms that can inhibit or kill the growth of bacteria. Fungi and bacteria can act as a source of antibiotics. Penicillin is released by the fungus Penicillium and streptomycin is released by the bacterium Streptomyces.

Answer:

Some animals act as intermediates and carry the infecting agents from a sick person to another potential host. These animals are called vectors. Diseases that are transmitted through vectors are:
1. Malaria (female mosquitoes),
2. Diarrhoea (flies) and
3. Dengue (female mosquitoes).
 

Answer:

(a) A balanced diet contains adequate quantities of carbohydrates, fats, proteins, vitamins and minerals that provide energy and helps in proper growth and development. Thus, providing a healthy body.
(b) Health is a person's physical, mental and social well-being. A person must live in a friendly atmosphere to be mentally and emotionally fit. Similarly, the environment should also be clean. A dirty, unhygienic environment may give rise to several infectious diseases.
(c) Stagnant water is the breeding ground of mosquitoes. Mosquito lay eggs in stagnant water. Female mosquitoes feed on human blood and spread the pathogen of malaria, dengue etc. Thus, our surrounding area should be free of stagnant water.
(d) Social harmony provides a healthy environment where neighbours, friends and family help each other. This creates a healthy mind space. Good economic conditions are needed to build and maintain a good infrastructure of the society as well as treatment of some diseases is also very costly. So, social harmony and good economic conditions are necessary for good health.

Answer:

The word 'disease' means discomfort-ease. Any deviation from the mental, physical or social well-being is called disease.
Diseases may be of four types:
1. Acute disease: Diseases that last for a short period of time are called acute diseases. Example: common cold, headache etc.
2. Chronic disease: Diseases that can last for a long time, even as much as a lifetime, and are called chronic diseases. Example: tuberculosis, elephantiasis.
3. Infectious disease: Diseases, where microbes are the immediate causes, are called infectious diseases. Such diseases can spread from an infected person to a non-infected person. Thus, communicable in nature. Example: pneumonia, cholera etc.
4. Non-infectious disease: Diseases that are non-communicable in nature, that is, they do not spread from an affected individual to a healthy individual, are called non-infectious diseases. Example: heart attack, diabetes etc.

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Symptoms are the medical indications a person shows when one or several systems in his body is not working properly. Symptoms may be mild to severe depending on the type of the disease. Signs of disease are what physicians will look for on the basis of the symptoms.
For example, a person may develop mild headache and fever due to exam anxiety or a person may have severe headache and inflammation, high fever, stiff neck and vomiting due to meningitis.

Answer:

The immune system of our body contains a number of cells that help to maintain the immunity of the body. When a pathogen enters inside the body, the cells of the immune system attack the pathogen and release certain chemicals to kill it. The pathogen is called antigen and the chemical released by the immune cells are called antibodies. Some immunity cells also engulf the antigen by phagocytosis to kill it. Thus, the immune system is essential for our health.

Answer:

Causes of diseases are various. Pathogens, infected food or water, unhealthy lifestyle etc. are some of the causes of diseases. A person might be cured after being diseased but there are certain limitations. First, the body of the patient or some of his organs may become permanently damaged. Second, some diseases may take longer to be cured. The third is that the person suffering from an infectious disease can serve as the source from where the infection may spread to other people. Hence, prevention is always better than cure. Some of the measures that can be taken to prevent diseases are:

1. Drink safe drinking water.
2. Eat a balanced diet.
3. Keep your surroundings clean.
4. Maintain personal hygiene.
5. Exercise regularly.
6. Maintain a peaceful atmosphere in your home and neighbourhood.
7. Always wash your hands before eating.
8. Brush and bath regularly.
9. Visit the doctor for regular medical checkups etc.

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The immune system of the body is not equally strong in every individual. Some children have strong immunity. They can prevent diseases easily. Whereas, some have poor immunity and fall sick easily. Besides the immune system, balanced diet, regular exercise and personal hygiene also plays an important role in maintaining a healthy body.

Answer:

Antibiotics are chemicals produced by microorganisms that can prevent the growth of the bacteria or kill the bacteria. Such antibiotics block the essential metabolic pathways of the bacteria. However, viruses being acellular, don't have their own cellular machinery. Once they infect host cells, they use host cells machinery to increase in number. So it is difficult to treat viral diseases with antibiotics.

Answer:

Becoming exposed to or infected with an infectious microbe does not necessarily mean developing the noticeable disease because our body has an immune system that acts as soldiers to kill the invading pathogens. The cells of the immune system produce antibody when an antigen attacks the body or kills it by engulfing the pathogen. Thus, diseases can not develop.

Answer:

Four factors that are necessary for a healthy person are:

1. To live in a clean and friendly environment.
2. Eating a balanced diet and drinking safe water.
3. Exercise regularly and maintain personal hygiene.
4. Proper immunisation to prevent diseases such as polio, tetanus etc.

Answer:

AIDS or acquired immunodeficiency syndrome is not a single disease but it develops a group of diseases. a person with AIDS has poor immunity thus he is much prone to infections. A common cold can lead to pneumonia or a minor gut infection can turn into diarrhoea in an AIDS-infected person. Thus, AIDS is considered as 'syndrome', that is, a person having AIDS has a group of diseases.