Friday 19 October 2012

CBSE Class 9 - Science - CH 13 - Why do We fall iLL

H1N1 Virus
3D image of FluVirus
(credits: PHIL)
(NCERT Chapter Solutions, Q &A)
Q1: Define Health? What do you interpret when we say a person is in good health?

Answer: Health is a state of physical, mental and social well-being of an individual not merely absence of a disease or infirmity.

When we say a person is in good health, it implies the different body systems and organs of that person function well and as a whole body strike a balance with the physical, mental and social environment.

Q2(NCERT): State any two conditions essential for good health.

Answer: Conditions essential for good health are:
  1. Physically fit and healthy.
  2. Cleanliness: habitat should be neat and clean.
  3. Good social and economic conditions.

3 dimensions of health
Q3: What are three dimensions of health? Are they interrelated?

Answer: The three dimensions of health are:
  1. Physical Dimension: A person is disease free, his/her skin is shining, has bright eyes, normal metabolism etc. define the physical dimensions of being healthy.
  2. Mental Dimension: Able to judge his strengths and weaknesses, does not overestimate or underestimate things etc.
  3. Social Dimension: Able to adjust with his/her family members and society, free from interpersonal conflicts etc. 

Q4: Kidneys of a person do not filter urine properly. How does it affect physical, mental and social dimensions of that person?

Answer:  If the kidneys of the person do not filter urine, the toxic substances will start collecting in the body and affect other organ systems. In such conditions, the brain will not think properly. The person will stay socially isolated, his physical movement will be restricted.

Q5(NCERT): State any two conditions essential for being free of disease.

Answer: Conditions essential for being free of disease are:
  • Personal Hygiene
  • Community Hygiene
  • Balanced Diet
Q6(NCERT): Are the answers to the above questions (Q2 and Q5) and necessarily the same or different? Why? 

Answer: Yes the answers to these questions are inter-related. Personal and community hygiene and cleanliness reduces the risk of getting any infection or being unhealthy. Physical exercise keeps the body function normally and prepares it to fight against any disease.

Q7: What is a balanced diet?

Answer: A balanced diet is one that provides all the required nutrients to the body in correct proportion. It includes the correct proportion of carbohydrates, proteins, vitamins, minerals and roughage in your diet.

Q8(CBSE 2011): A hefty boy of 12 years often picks fights with others. Do you think he is in good health? If so, then explain your answer.

Answer: No the boy is not in good health. His persistent impulsiveness (constant fighting with others) indicates that the boy may have mental and/or social issues. He does not feel empathy when others are hurt. It tells he may be psychologically "unhealthy".

Q9: (i) How do you define 'disease'?
(ii) (CBSE 2011) State and explain in brief the four major factors, which are the causes of disease. 

Answer: The condition of malfunctioning of the organ system or systems is called disease. In layman terms, disease means "without ease". The disease leads to an abnormal condition in which our body or body organ does not work properly.

Following are the major factors which cause diseases:
  1. pathogens (e.g. virus, bacteria, worms etc.)
  2. environmental factors (e.g. pollutants)
  3. nutritional factors (e.g. malnutrition)
  4. genetic factors (e.g. gene defects)
  5. hormonal imbalances (e.g. insufficient release of insulin causes diabetes)
  6. metabolic factors (e.g. organ failure)
Q10: Is there any difference between 'being healthy' and 'disease free'?

Answer: Yes there is a difference between the two. A person may be in poor health but he is not suffering from any disease. Having poor health increases the risk that he may suffer from any disease. In general, when we talk think about health, we think of society or community level. When we talk about the disease, we think about individual sufferers.

Q11: How do we identify a disease?

Answer: By looking at symptoms and signs.

Q12: What is the difference between symptoms and signs of a disease?


Symptoms         Signs
1. Symptoms are the indicators that there is some abnormality in the body.1. Signs provide information about the possibility of a particular disease.

2. In general, symptoms are the problems which a patient feels or notices.                     2. Signs are the indications which the doctors find objectively.
3. e.g. Patient feels hot and body ache which is symptoms.3. Doctors examine the patient and find the skin is hot and measures patient's body temperature which is the signs.

Q13(NCERT): List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?

Answer: Symptoms that make me sick:
  • Cough
  • Fever
  • Constant Headache
Yes, I will still visit the doctor if only one of this symptom is present because it makes me uncomfortable and bed-ridden. Ignoring the symptom for a longer duration may have serious consequences.

Q14: Based on duration or persistence, how diseases are categorised?

Answer: Based on duration or persistence, diseases are categorised as:
  • Acute Diseases
  • Chronic Diseases
Diseases can be categorised in different ways, a few are depicted here:
Classification of Diseases
Different Ways to classify

Q15(NCERT): 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. Why? 

Answer: (a) Jaundice is a chronic disease in which liver is affected. Jaundice has long-term effects on the body. It will take a long time to recover.

(b) Lice can be treated easily and have short-term effect on our health.

(c) Acne may exist for a longer time but do not have any adverse effect on our health.

Q16: Give examples of Acute diseases.

Answer: A cough, Common Cold, Typhoid, Cholera

Q17: Give four examples of Chronic diseases.

Answer: Elephantiasis, Tuberculosis, diabetes, arthritis etc.

Q18: Differentiate between Acute Diseases and Chronic Diseases.

No.Acute DiseasesChronic Diseases
1.Symptoms last for a short period of time.Symptoms persist for a longer duration and may last a lifetime.
2.Generally sudden onset of disease or injury.Diseases develop slowly and gradually.
3.Patient may recover fast after the treatment and is free from symptoms.Patient does not recover completely. It takes a longer time to get relief.
4.May not require hospitalisation.May require hospitalisation and long duration treatment.
5.Examples: Influenza, Common Cold, bad throat, a small injury like cut in finger etc.Examples: Diabetes, Tuberculosis, Arthritis, Heart Diseases etc.

Cleft lip (congenital disease)
Cleft lip (congenital disease)
Q19: What are congenital diseases? Give two examples of such disease.

Answer: Congenital diseases refer to diseases or abnormalities present since birth. It may be due to gene mutations (genetic factor) or environmental factors.
Examples: Colour blindness, Down's syndrome, cleft lip or palate.

Q20: Name a disease which was earlier considered to be chronic but now can be treated in short duration?

Answer: Peptic ulcer.

Q21(NCERT): 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?

Answer: (a) Various symptoms can help us find if a baby is sick or not:
  1. constant crying, 
  2. frequent loose motions
  3. disrupted sleep or unusual long sleep
  4. vomiting etc.
 (b) An examination and diagnosis of symptoms and signs of the baby by a doctor will help in identifying the particular disease.

Q22: What are acquired diseases? 

Answer: The diseases which develop after birth are called acquired diseases. These are classified as:
  1. Communicable or Infectious Diseases: malaria, influenza etc.
  2. Non-communicable Diseases: diabetes, scurvy, high blood pressure

Q23(CBSE 2011): Write few common signs and symptoms of a disease if a brain is affected.

Answer: A headache, fits, unconsciousness, vomiting etc.

Q24(CBSE 2011): List any two differences between infectious and non-infectious diseases. Write any one example of each disease.


Infectious Diseases               Non-Infectious Diseases
1. Caused by external factors e.g. pathogens
1. Caused by internal factors e.g. genetic abnormality
2. Diseases can spread unhealthy person to healthy person.2. Diseases do not spread from infected to a healthy person.
3. Infection can spread and infect others via direct contact or medium (air, water, vectors etc.)3.Infection does not spread through direct contact nor by the medium. However, it may be hereditary i.e. from parents to offspring.
4. Examples: Malaria, Dengue etc.4. Examples: Goitre, High Blood pressure, Diabetes

Q25(CBSE 2010): What are infectious agents? What are the different infectious agents?

Answer: The microorganisms which spread the disease from one person to other are called
infectious agents. Different infectious or causative agents or pathogens are:
  1. Viruses
  2. Bacteria
  3. Fungi
  4. Protozoans
  5. Worms
Q26: What is 'germ theory of disease'? Who proposed it?

Answer: Louis Pasteur proposed 'germ theory of disease. Accord to this theory he stated that micro-organisms are the causes of many diseases. It is also called the pathogenic theory of medicine.

Q27: What are Koch's Postulates?
Answer:  Robert Koch proposed four postulates to identify the causative agent of a particular disease. These postulates are:
  1. The microorganism or other pathogens must be present in all cases of the disease.
  2. Pathogens can be isolated from the diseased host and grown in pure culture.
  3. Pathogens from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.
  4. Pathogen must be re-isolated from the new host and shown to be the same as the originally inoculated pathogen
Q28: List the diseases caused by viruses?

Answer: Diseases caused by viruses:
  1. Influenza
  2. Dengue fever
  3. Common Cold
  4. AIDS
  5. Chicken Pox
  6. Measles
  7. Hepatitis

Q29: Give three examples of bacterial diseases.

Answers: Examples of bacterial diseases are:
  1. Tuberculosis
  2. Anthrax
  3. Typhoid
  4. Tetanus

Q30: Give examples of fungal diseases.

Answer: Fungal infections are:
  1. Common skin infections e.g. Ringworm, Athlete's foot
  2. Aspergillus infects lungs

Q31: List three diseases caused by protozoans.

Answer: Diseases caused by protozoans:
  1. Kala-azar (Leishmaniasis)
  2. Malaria
  3. Amoebiasis 
  4. African Sleeping Sickness

Q32: Name the pathogen causes peptic ulcer.

Answer: Helicobacter pylori (bacteria)

Q33: List the diseases caused by worms?

Answer: Elephantiasis, Intestinal infections.

Q34: Name the protozoan pathogen that causes kala-azar.

Answer: Leishmania

Q35: Name the microbe which causes acne.

Answer: staphylococci (a type of bacteria).

Q36: What is the scientific name of roundworm? Where do we find it commonly in the human body? Name the disease caused by it.

Answer: Ascaris lumbricoides. Generally found in the human intestine. Ascariasis.

Q37: Why is it important that we think of these categories of infectious agents?

Answer: Members of each one of these groups – viruses, bacteria, and so on – have many biological characteristics in common. these categories are important factors in deciding what kind of treatment to use. It implies many important life processes are similar in the bacteria group but are not shared with the virus group. As a result, drugs that block one of these life processes in one member of the group is likely to be effective against many other members of the group. But the same drug will not work against a microbe belonging to a different group.

Q38: How do antibiotics (say Penicillin) work on bacteria but not on human beings?
Q(CBSE 2011): Define antibiotic? Explain how it is able to control bacterial infections but not viral

Answer:  Antibiotics (anti means against, biotic - living) are types of medications that destroy or slow the growth of bacteria. They are often termed as antibacterials. They work against the life processes of bacteria. They commonly block biochemical pathways important for bacteria. Many bacteria, for example, make a cell-wall to protect themselves. The antibiotic penicillin blocks the bacterial processes that build the cell wall. Thus bacteria fail to build their cell-wall, stop multiplying and die out. Human cells don’t make a cell-wall anyway so penicillin cannot have such an effect on us.

Q39(CBSE 2011): Explain why antibiotics are more effective in curing bacterial diseases than viral diseases.

Q: Why taking an antibiotic is not effective in the common cold?

Answer: Antibiotics are effective in curing bacterial and fungal infections (e.g. tuberculosis)  but they are ineffective in viral diseases (like the common cold). Antibiotics affect on life processes of bacteria and inhibit their growth. On the other hand, virus is just a piece of DNA (or RNA), not a well-defined life form. Viruses can reproduce inside host cells. They do not use common biochemical pathways as used by other microbes (bacteria, fungi and parasites). That's why antibiotics are ineffective in viral infections.
It should be noted that despite this limitation, there are now effective anti-viral drugs, for example, the drugs that keep HIV infection under control.

Q40(HOTS): Give two examples of bacterial antibiotics.

Answer: Antibiotics used to kill bacterial infections:
  1. penicillin, ampicillin: inhibits synthesis of a cell wall.
  2. streptomycin, tetracycline: prevent protein synthesis in ribosomes.

Q41(HOTS): Give an example of fungal antibiotic.

Answer: polyoxin: inhibits cell wall growth in fungi.

Q42(NCERT): Why are we normally advised to take bland and nourishing food when we are sick?

Answer: When we are sick, generally it affects on our digestion and we lose appetite. Bland food is low-fibre, non-spicy and easy to digest food. It helps in digestion and provides necessary nourishment. In a case of patients suffering from gastrointestinal problems like ulcer, bland diet helps recover from such problems. Bland diet helps in improving the immunity and regeneration of healthy body tissues.
On the other hand oily, spicy and fried food cannot be easily digested by sick patients and this food is not recommended.

Q43(NCERT): What are the different means by which infectious diseases are spread?

Answer: Infectious diseases can spread through various means like through air, water, by direct and indirect contact, vectors (animals, mosquitos, flies etc.).

  1. Through Air: Spread through sneezing, coughing, open defecation. Air Borne Diseases are common cold, pneumonia, tuberculosis, measles, SARS, chicken-pox.
  2. Through Water: open defecation,  consuming contaminated water, inadequate hand washing. Water-borne diseases are cholera, amoebiasis, typhoid etc.
  3. Direct Contact(including sexual contact): By handshaking, kissing, contact with body lesions, sexual contact. e.g. common cold, tuberculosis, chicken pox, warts etc. Sex Transmitted diseases (STD) are Syphilis, AIDS, gonorrhoea.
  4. Indirect Contact:  By frequently touching the surfaces of objects used by infected persons e.g. touching doorknobs, utensils, clothes, towels, toilets, computer keyboards etc. Examples of diseases spread by Indirect Contact are Flu, TB, Chickenpox, urinal infections etc.
  5. Through vectors: Animals, Flies, Mosquitos etc. carry infecting agent from sick person to healthy person. Vector-borne diseases are rabies, malaria, dengue, yellow fever, dysentery, diarrhoea etc.
Q44(MCQ): If a person has a persistent cough and breathlessness, most likely which of the following organ is affected

(a) lungs
Female Anopheles
Female Anopheles
(b) liver
(c) brain
(d) intestinal tract

Answer: (a) lungs

Q45: What is the alternate name of brain fever? Which vector is responsible for this disease?

Answer:  Japanese encephalitis caused by a virus which enters through a mosquito bite.

Aedes aegypti
Aedes aegypti
Q46: Name the vector which causes malaria.

Answer: Female Anopheles mosquito.

Q47: Name the vector which causes dengue, chikungunya and yellow fever.

Answer: Aedes aegypti mosquito

Q48: Name the vector that can cause sleeping sickness.

Answer: Tsetse Fly

Q49: Name the diseases that can spread through housefly.

Answer: Cholera, Typhoid, Dysentery, Diarrhoea, Tuberculosis etc. may spread via houseflies.

Q50: Name the vectors which can cause rabies.

Answer: Most of the animals included humans can be infected and all of them can spread the disease. Dogs, rats, cats, monkeys, squirrels, cattle, wolves, racoons, bears etc. can spread this disease. In India, mostly it spreads through dog bites and monkey bites.

Q51(NCERT): 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.

Answer: A doctor or a nurse or a health worker avoids getting sick by taking the following precautions:
  • keep the workplace (hospital and surroundings) sterilised.
  • use sterilised equipment and disposable syringes.
  • use hand gloves, masks and wash their hands after examining a patient. 
  • immunised themselves with different vaccinations.
  • keep themselves fit by regular exercise and balanced diet.
  • create awareness among co-workers and educate people about cleanliness, regular exercise and healthy diet.

Q52(NCERT): What precautions can you take in your school to reduce the incidence of infectious diseases?

Answer: To reduce the incidence of infectious diseases, following precautions can be taken in schools:
  • provide clean and safe drinking water
  • proper sanitation and cleanliness in school premises and its surroundings and not to allow any mosquitoes (vector) breeding.
  • encouraging students and their parents to take vaccinations against infectious diseases.
  • encourage students and teaching staff to stay home and seek medical advice when infected.
  • aware students about hygienic practices like wash hands before taking food and after going to the washroom. And cover face while sneezing etc.
  • encourage students to adopt healthy eating practices e.g. adopt fruit+salad food breaks.

Q53: What do you mean by immunity?

Answer: The ability of the body to be resistant towards injury, poison or harmful pathogens and their products is called immunity. It is part of the defence reaction in the body.
There are two types of immunity:
  • Natural or Innate immunity.
  • Acquired or Specific immunity


Q54(NCERT): What is immunisation?

Answer: Administering vaccines to prevent the disease is called immunisation. Immunisation is a technique to prevent infectious disease. In this technique, vaccines are given into the people so that they develop temporary or permanent immunity (Artificial Active Acquired Immunity) to fight against a particular disease.

Q55: What is antigen?

Answer: When a pathogen invades our body, it releases toxins into bloodstream or in tissues. This toxin or foreign protein entering our body is called antigen.

Q56: What are antibodies?

Answer: The proteins produced by our immunity system (lymphocytes, WBCs etc.) to neutralise or detoxify antigens are called antibodies.

Q57: What is colostrum? Why is mother's milk strongly advised to newborns?

Answer:  Colostrum also called first milk is the milk produced by the mother in late pregnancy. It is rich in antibodies. Newborn babies have weak immunity system at birth. Through mother's milk, antibodies are transferred to the baby. It persists in the baby’s body for several weeks and provides her passive immunity to fight against many diseases.

Q58(NCERT): 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?

Answer: At the nearest health centre various immunisation programmes are available, such as:
  • Polio eradication programme
  • Hepatitis vaccination programme
  • Tuberculosis prevention programme
To mothers immunisation schedule is given for their newborns:

Recommended Immunisation Schedule

S.No.AgeDisease              Vaccination
1At Birth    Hepatitis B            Hep B Vaccine I
2At BirthPolioOral PV 0 dose
3Birth to 6 wkTuberculosisBCG
44 6 weeksHepatitis BHep B Vaccine II
56 weeksDiphtheria, Pertussis,
Tetanus, Polio
DPT-1, OPV-1
610 weeksDiphtheria, Pertussis,
Tetanus, Polio,
Hepatitis B
Vaccine III
714 weeksDiphtheria, Pertussis,
Tetanus, Polio
Vaccine IV
824 weeksHepatitis BHEP B
Vaccine III
99- 12 monthsPolio MeaslesOPV-4, Measles
1015 - 18 monthsMumps, Measles,
1118 monthsDiphtheria, Pertussis,
Tetanus, Polio
1224 monthsTyphoidTyphoid
124 - 5 yearsDiphtheria, Pertussis,
Tetanus, Polio

Watch video: What Deadly Diseases Look Like On Our Body. Vaccines help in reducing the mortality rate.

Q59(CBSE 2011): (a) What are epidemic and endemic diseases? 
(b) Which organ is affected if a person is suffering from jaundice?

Answer:  (a) A disease or condition which affects a large number of people at the same time is called an epidemic. e.g. an outbreak of plague in China in 2009.

An Endemic disease is a disease or condition that is constantly present in a particular community or localised region. e.g. Hepatitis A, Malaria, Dengue are endemic in India.

(b) Jaundice or hepatitis is a viral disease which affects the liver.

Q60: What do you mean by Phagocytosis?

Answer: WBCs or leukocytes play an important role in a defence mechanism of a body. When a foreign body or microbe (e.g. bacterium) enters the blood stream, leukocytes surround the microbe and engulf them. Thus the microbes are destroyed. This process of engulfing and destroying foreign bodies is called phagocytosis.

Q61: Why is it not necessary to give Hepatitis A vaccine to children?

Answer: Hepatitis A, a type of jaundice is caused by a virus. This virus is transmitted through water. In many regions of India, this virus is found in drinking water. By the time the children reach age of five for Hepatitis A vaccination, they already have become immune to this disease. Therefore it is not necessary to give Hepatitis A vaccine to children.

See Quiz on Why do we Fall Ill?

Q62: What are the basic principles involved in medical treatment for diseases?

Answers: The basic principles involved in medical treatments are:
  1. Minimise the impact of disease on a human body.
  2. Kill or eliminate disease-causing germs.
  3. Help in providing immunity of the body.

Q63: Why it is advisable to breast feed the baby for first few several weeks? 
Why Colostrum is good for infants?

Answer: Infants or babies after birth do not have strong immune system. The colostrum or mother's milk contains many antibodies which provide passive immunity to the babies. Therefore it is advisable to breast feed the baby for first few several weeks.

Q64: How do Skin, Hairs, Saliva form the first line of defence against diseases?

Answer: Skin, Nose hairs, Saliva act as the first line of defence.
Skin: It forms a physical barrier thus preventing the entry of microbes.
Hairs: Prevent entering dust particles and germs.
Saliva: It washes away bacterial growth from teeth and mouth.

Q 65 (HOTS): Why are kids and elderly people more vulnerable to cold/flu?

Answer: Kids are more vulnerable to cold and flu because their immune systems haven't fully developed. Elderly people also more prone to catch a cold because of their poor health.

Q 66 (HOTS): Why do people staying in air-conditioned homes/offices catch cold more often?

Answer: The indoor climate due to air-conditioning is drier due to which the cold virus can stay longer in air infecting more people.


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