SEBA Class 9 Science Chapter 13 Why Do We Fall Ill Extra Question Answer Solutions (New Syllabus 2026–27)

Looking for reliable SEBA Class 9 Science Chapter 13 (Why Do We Fall Ill) extra questions and answers for the 2026–27 academic year? Access important short questions, conceptual explanations on healthy vs. disease-free states, pathogen types, principles of prevention and treatment, and exam-focused revision notes to score top marks.

Extra question and answer

Q1. Why do we say that health and disease are complex issues in human communities?

Answer:

Health and disease are complex because many factors affect them at the same time. These include personal hygiene, food, environment, economic conditions, and social habits. Also, different people may have different causes for the same illness. So, understanding health and disease requires looking at many interconnected causes, not just one reason.

Q2. Why is understanding the meaning of ‘health’ and ‘disease’ important before studying their causes?

Ans.

To prevent or treat diseases properly, we must first understand what “health” and “disease” mean. If we know what a healthy body needs, we can identify what is going wrong when disease occurs. This helps in finding correct causes and correct methods of prevention and treatment.

Q3. How are cells important for understanding health and disease?

Ans.

Cells are the basic units of life, and all body functions depend on them. They constantly perform activities like repair, growth, and energy production. If something stops cells from working properly, tissues and organs stop working too, leading to disease. Therefore, disease usually starts with problems in cells.

Q4. Explain how different organs of the body are interconnected with an example.

Ans.

Organs depend on each other to work properly. For example, if the kidneys stop filtering urine, poisonous wastes build up in the blood. This affects the brain and it cannot think clearly. This shows that failure in one organ affects other organs too.

Q5. Why is food essential for maintaining health?

Ans.

Food provides energy and raw materials for the body. Cells use proteins, carbohydrates, fats, and minerals from food to carry out repair, growth, and daily functions. Without proper food, cells and tissues cannot perform their activities, leading to poor health.

Q6. What happens when cells and tissues are not able to function properly?

Ans.

If cells and tissues stop functioning properly, the activities of the whole body get disturbed. Organs may not perform their tasks—like filtering, breathing, or thinking. As a result, the person becomes sick and may develop a disease.

Q7. How does the passage explain the link between cell activity and overall health?

Ans.

The passage explains that all body activities—like heartbeat, breathing, and thinking—depend on the work of cells. Cells need constant energy and materials, which come from food. If cell activities are disturbed, the whole body’s functions suffer, leading to disease. So, proper cell activity is necessary for good health.

Q8. What does the term ‘health’ mean?
Ans.
Health means a state of being well enough to function properly in daily life. It includes physical well-being (strong body), mental well-being (positive thinking), and social well-being (good relations with others). A healthy person can do everyday tasks comfortably.

Q9. How does the passage explain ‘being well’? Give examples.
Ans.
Being well means being able to perform normal activities without difficulty. For example, a grandmother going to the market or visiting neighbours shows she is well. Similarly, a student listening and taking interest in classroom teaching shows mental well-being. Not being able to do these things shows poor health.

Q10. Why is health considered a combination of physical, mental and social well-being?
Ans.
Health is not only about the body. A person must also think positively (mental well-being) and have good relationships with others (social well-being). If any one of these is affected, the person cannot function properly. So, true health means being well in all three areas.

Q11. Why does the passage say health is related to effective functioning?
Ans.
Health allows a person to carry out daily activities effectively. If someone is healthy, they can work, study, interact with others, and enjoy life. But if they are unwell, these activities become difficult. Thus, health directly affects how well a person functions.

Q12. Explain with examples how different people understand ‘health’ differently.
Ans.
People understand health based on their needs. For an elderly person, walking outside or visiting neighbours means good health. For students, showing interest in studies and understanding lessons is considered a healthy attitude. Thus, the idea of health changes with age and situations.

Q13. Why can health not be achieved by an individual alone?
Ans.
Health cannot be achieved by an individual alone because it depends on our surroundings and environment. Clean water, sanitation, garbage disposal, and disease-free surroundings require community effort. If the environment is unhealthy, even a healthy person can fall sick. So both personal effort and community conditions are important.

Q14. How does our physical environment affect our health?
Ans.
Our physical environment includes the air we breathe, water we drink, and cleanliness around us. Events like cyclones can damage houses, contaminate water, and spread diseases, affecting health. Similarly, dirty surroundings or stagnant water increase the risk of infections. Thus, a safe physical environment is essential for good health.

Q15. How does the social environment influence individual health?
Ans.
Humans live in societies where social conditions decide the quality of life. If people live in fear, face discrimination, or lack harmony, mental and social well-being is affected. Supportive and peaceful social surroundings help people stay happy and healthy. Therefore, social equality and good relationships are important for better health.

Q16. Why are public cleanliness and sanitation necessary for individual health?
Ans.
If garbage is not collected and drains are not cleaned, mosquitoes and germs can breed. Stagnant water and dirty surroundings increase the chances of diseases like malaria, dengue, and diarrhea. Proper sanitation prevents infections and keeps the environment safe. Hence, public cleanliness directly supports the health of every individual.

Q17. Explain why opportunities to work are important for maintaining health.
Ans.
People need food for good health, and food is earned by working. If opportunities to work are limited, people cannot earn enough to buy healthy food or access healthcare. Unemployment also leads to stress, affecting mental health. Thus, economic security and work opportunities are essential for overall well-being.

Q18. What is the difference between being ‘healthy’ and being ‘disease-free’?
Ans.
Being disease-free means that a person does not show any signs of a particular illness. However, being healthy is a much broader idea — it includes physical, mental, and social well-being. A person may not have any disease but may still be unhappy, weak, stressed, or unable to perform daily activities. Therefore, a person can be disease-free without actually being healthy.

Q19. Why does the term ‘disease’ mean “disturbed ease”? Explain with an example.
Ans.
The word “disease” literally means the loss of ease or comfort — dis + ease. It refers to a condition where normal body functions are disturbed and cause discomfort. For example, in diarrhoea, a person has loose motions and feels weak and uneasy. Thus, a disease clearly shows that something in the body is not functioning normally.

Q20. Why is it possible to be in poor health even without having a specific disease?
Ans.
Poor health can result from factors other than diseases, such as lack of sleep, poor nutrition, stress, unhygienic surroundings, or unhappiness. These do not always lead to a diagnosable disease but still reduce physical, mental, or social well-being. Therefore, a person may not have a disease but may still be unhealthy.

SEBA Class 9 Science Chapter 13 Extra Questions

Q21. Why does the idea of health include the ability to realise one’s full potential?
Ans.
Good health means more than the absence of disease — it means being able to perform tasks efficiently and achieve one’s goals. For example, a dancer needs flexibility, while a musician requires good breathing capacity. Only when people are healthy can they fully use their abilities and talents. Hence, reaching one’s potential is an important part of true health.

Q22. Why do we think about societies and communities when we talk about health, but think about individuals when we talk about disease?
Ans.
Health depends on social and environmental factors such as clean surroundings, safe water, job opportunities, and supportive communities. These conditions are created by society as a whole, not by individuals alone. However, a disease affects the body of a specific person and is diagnosed individually. Thus, health is a community issue, while disease is an individual issue.

Q23. What are symptoms and signs of a disease? Explain with examples.
Ans.
Symptoms are the changes in the body that we feel when something is wrong. They tell us that a disease may be present but do not specify which disease it is. Examples: headache, cough, loose motions, pus in a wound.
Signs are changes that a physician observes during examination. They help in identifying the exact disease. Doctors may use laboratory tests to confirm these signs.

Q24. Why do symptoms alone not help in identifying a specific disease?
Ans.
Symptoms only show that something is wrong in the body, but the same symptom can occur in many different diseases. For example, a headache may be due to stress, lack of sleep, dehydration, or even meningitis. Because symptoms are not specific, doctors need signs and laboratory tests to find the exact cause of illness.

Q25. What are acute diseases? Give examples.
Ans.
Acute diseases are diseases that last for a very short period of time. They start suddenly and usually end quickly. Example: The common cold lasts only a few days. Fever or diarrhoea may also be acute. These conditions do not stay in the body for long.

Q26. What are chronic diseases? Give examples.
Ans.
Chronic diseases are diseases that last for a long time, sometimes for months, years, or even a lifetime. Examples: Elephantiasis, which is common in some parts of India, and asthma. These diseases develop slowly and have long-lasting effects on health.

Q27. How do acute and chronic diseases differ in their effect on health?
Ans.
Acute diseases last for a short time, so they usually do not cause major or long-term damage to the body. For example, common cold or cough makes us unwell for a few days, but we recover quickly. Chronic diseases last for a long time, often years, and cause continuous poor functioning of body parts. This leads to long-term poor health, weakness, and inability to do daily activities.

Q28. Why do chronic diseases lead to long-term poor health?
Ans.
Chronic diseases stay in the body for many months or years, so they continuously disturb the normal functioning of organs. For example, in tuberculosis of the lungs, the person may lose weight, feel tired all the time, and become weak. This long-lasting illness reduces a person’s strength and learning ability, leading to prolonged poor health.

Q29. Give an example to show that acute diseases do not cause lasting health problems.
Ans.
A common cold or cough is an acute disease. It lasts only a few days, and after taking rest and proper care, most people recover fully within a week. There are no permanent or long-term effects on the body, which shows that acute diseases do not harm health for long.

Q30. How can chronic diseases affect learning and daily life?
Ans.
Chronic diseases keep a person ill for a long time, making them weak and tired. Because of this, they may miss school frequently and find it difficult to concentrate or follow lessons. This reduces their ability to learn and affects their mental and physical performance in daily activities.

Class 9 Science Chapter 13 Important Questions SEBA 2026-27

Q31. Why do diseases have more than one cause?
Ans.
Diseases often do not occur due to a single factor. They happen because of a combination of immediate causes (like infection) and contributory causes (like poor nutrition, poverty, or lack of clean water). For example, a baby may get loose motions due to an infection, but poor nourishment or weak immunity may make the baby more likely to fall ill. Therefore, diseases have multiple interconnected causes.

Q32. What is the difference between immediate and contributory causes of a disease?
Ans.
Immediate causes are the direct reasons for a disease, such as infection by a pathogen that directly produces symptoms. Contributory causes are the supporting factors that make a person more likely to get the disease, such as poor nutrition, poverty, lack of clean drinking water, or weak immunity. Both kinds of causes together determine whether a person develops the disease.

Q33. How can poor public services contribute to diseases?
Ans.
Poor public services may lead to unsafe drinking water, improper garbage disposal, or lack of sanitation. These conditions allow disease-causing organisms to spread easily. For example, if clean drinking water is not provided, babies may get infections causing loose motions. Thus, lack of proper public services becomes an indirect but important cause of diseases.

Q34. Give an example to show that contributory causes also lead to disease.
Ans.
A baby who drinks unclean water may get infected, but only the weaker or poorly nourished baby may develop loose motions. Here, the infection is the immediate cause, but poor nourishment and weak health are contributory causes that make the disease more likely.

Q35. What are infectious diseases? Give one example.
Ans.
Infectious diseases are illnesses caused by microbes or micro-organisms, such as bacteria, viruses, fungi, or protozoa. These microbes act as immediate causes and can spread from one person to another, making the disease contagious. Example: Common cold or tuberculosis.

Q36. What are non-infectious diseases? Give one example.
Ans.
Non-infectious diseases are illnesses not caused by microbes. Their causes are usually internal, such as genetic disorders, lifestyle factors, or organ malfunction. These diseases do not spread from person to person. Example: High blood pressure or diabetes.

Q37. How do infectious and non-infectious diseases differ in their prevention and treatment?
Ans.
Since infectious diseases spread through microbes, their prevention focuses on controlling the spread, maintaining hygiene, vaccinations, and ensuring clean surroundings. Treatment often includes medicines that kill or stop microbes. Non-infectious diseases need individual-based prevention, such as healthy lifestyle, balanced diet, exercise, and sometimes long-term treatment like insulin or surgery. The methods differ because their causes are different.

Q38. Why is it important to distinguish between infectious and non-infectious causes of diseases?
Ans.
Distinguishing them helps us decide how the disease spreads, what precautions are needed, and the best method of treatment. Infectious diseases need community-level actions like sanitation and vaccination. Non-infectious diseases require personal lifestyle changes or genetic care. Understanding the type of cause helps in effective prevention and control.

Q39. What are infectious agents? Give two examples from different categories.
Ans.
Infectious agents are living organisms that cause diseases in humans. They belong to different biological groups such as viruses, bacteria, fungi, protozoa, and worms.
Examples:

Virus – Dengue virus

Bacterium – Mycobacterium tuberculosis (causes TB)

Q40. Why is it important to classify infectious agents into groups like viruses, bacteria, fungi, and protozoa?
Ans.
Classifying infectious agents is important because each group has different biological characteristics. This helps doctors decide the correct treatment. For example, bacteria have a cell wall and can be killed by antibiotics, whereas viruses live inside host cells and do not respond to antibiotics. Therefore, knowing the type of infectious agent helps in choosing the right medicine.

Why Do We Fall Ill Class 9 SEBA Extra Question Answer

Q41. Why are antibiotics effective against bacteria but not against viruses?
Answer:
Antibiotics work by blocking biochemical pathways used by bacteria, such as building the cell wall. Viruses do not have a cell wall and do not use these bacterial pathways, so antibiotics cannot affect them. Thus, antibiotics cure bacterial diseases but do not reduce the severity or duration of viral diseases like the common cold.

Q42. Give two examples each of diseases caused by viruses, bacteria, fungi, protozoa, and worms.
Answer:

Q43. How does the rate of multiplication of microbes affect the severity of infection?
Answer:
Microbes like viruses, bacteria, and fungi multiply very quickly, so their infections spread fast and show symptoms earlier. Worms multiply very slowly, so their infections take longer to show effects but may cause long-term problems. The multiplication rate therefore influences how fast the disease appears and how serious it becomes.

Q44. Explain how penicillin works on bacteria but does not harm human cells.
Answer:
Penicillin blocks the process that bacteria use to build their cell walls. Without a cell wall, bacteria die easily. Human cells do not have cell walls, so penicillin does not affect them. This makes penicillin safe for humans but deadly for bacteria.

Q45. What are communicable diseases? How do they spread through air?
Answer:
Communicable diseases are diseases that can spread from an infected person to a healthy person through different means. They spread through air when an infected person coughs or sneezes, releasing tiny droplets containing microbes. A nearby healthy person may breathe in these droplets, allowing the microbes to enter the body. Examples: Common cold, pneumonia, tuberculosis.

Q46. How do diseases spread through contaminated water? Give an example.
Answer:
Diseases spread through water when excreta of an infected person containing microbes mixes with drinking water used by others. When people drink this contaminated water, the microbes enter their body and cause infection. Example: Cholera spreads through contaminated water. These diseases spread more easily when there is poor sanitation and lack of safe drinking water.

Q47. Explain how sexually transmitted diseases (STDs) spread. Give two examples.
Answer:
Sexually transmitted diseases spread through close physical contact during sexual activity between two people. The microbes are passed directly from the infected partner to the healthy partner.

Examples:

Q48. Besides sexual contact, how else can HIV/AIDS spread?
Answer:
HIV/AIDS can also spread through blood-to-blood contact, such as:

Q49. What are vectors? How do they help in spreading diseases?
Answer:
Vectors are organisms (usually animals like insects) that carry disease-causing microbes from an infected person to a healthy person. Example: Mosquitoes act as vectors for malaria and dengue. Vectors pick up microbes from a sick person and transmit them to the next host, completing the chain of infection.

Q50. Why do airborne diseases spread more easily in crowded places?
Answer:
Airborne diseases spread through droplets released during coughing or sneezing. In crowded places, many people are close to each other, so more individuals can inhale the infected droplets quickly. As a result, diseases like common cold, tuberculosis, and pneumonia spread much faster in crowded environments.

SEBA Class 9 Science Chapter 13 Short Notes

Q51. What are the two main ways to treat an infectious disease?
Answer:
The two main ways to treat an infectious disease are:

Reduce the effects of the disease – by managing symptoms like fever, pain, or loose motions, and by taking rest.

Kill the cause of the disease – by using medicines that target and kill the microbes causing the infection, such as antibiotics or anti-protozoal drugs.

Q52. Why do symptom-directed treatments like rest and fever medicine not cure the disease?
Answer:
Symptom-directed treatments only reduce discomfort caused by the disease. They do not kill the microbes causing the infection. The infection can continue unless the microbes are eliminated using specific medicines.

Q53. How do antibiotics work to kill bacteria without harming human cells?
Answer:
Antibiotics target biochemical pathways specific to bacteria, such as the process of making cell walls. Human cells do not have cell walls and do not use these pathways, so antibiotics kill bacteria but do not harm human cells.

Q54. Why is it harder to make antiviral medicines compared to antibacterial medicines?
Answer:
Viruses enter human cells and use the cell’s machinery for their life processes. They have very few of their own biochemical mechanisms, so there are fewer virus-specific targets for medicines. This makes antiviral drugs harder to develop.

Q55. Give an example of an effective antiviral drug and its purpose.
Answer:
An example is the drugs used to control HIV infection. These antiviral medicines slow down the replication of the virus and help manage the disease, although they do not completely eliminate the virus from the body.

Q56. Why is prevention of diseases considered better than their cure?
Answer:
Prevention is better because once someone gets a disease:

Body functions may be permanently damaged.

Treatment takes time, keeping the person sick for days.

The disease can spread to others, causing more problems.

Q57. How can infectious diseases be prevented through environmental measures?
Answer:

Q58. What role does the immune system play in preventing infectious diseases?
Answer:
The immune system fights off microbes that enter the body. If it succeeds, infection does not cause noticeable disease. Proper nutrition and food are necessary for the immune system to function well.

Q59. What is the principle behind immunisation?
Answer:
Immunisation works by exposing the immune system to a harmless form of the microbe. The immune system develops memory, so if the actual microbe enters later, it is quickly eliminated, preventing the disease.

Q60. Give examples of vaccines used in childhood immunisation programmes.
Answer:
Vaccines are available for:

Class 9 Science Chapter 13 Important Short Questions

Q61. Why should all children have access to immunisation and public health measures?
Answer:
Effective prevention in a community requires universal access because if only some children are protected, the disease can still spread among those unprotected.

🔬 Updated Extra Questions Guide Notice: This page features an extensive collection of SEBA Class 9 Science Chapter 13 (Why Do We Fall Ill) Extra Questions and Detailed Answers updated for the 2026–27 academic session. All conceptual explanations on infectious agents, organ-specific manifestations, immunity, and public health principles strictly follow the latest revised Assam Board (SEBA) curriculum.

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