Here’s your concise guide to Class 9 Science Chapter 13: Why Do We Fall Ill! Ideal for Class 9 students, parents, and teachers prepping for the 2025 CBSE exams, this post covers in-text questions and answers, exercise solutions, and detailed notes on health and disease. Let’s dive into the Class 9 Science Chapter 13 questions, answers, and notes!
Class 9 Science Chapter 13 Notes
1. Health
- Definition: State of physical, mental, and social well-being, not just absence of disease.
- Factors: Balanced diet, hygiene, exercise, mental peace.
2. Disease
- Definition: Any condition impairing normal body function.
- Types:
- Acute: Short-term (e.g., cold).
- Chronic: Long-term (e.g., diabetes).
- Causes: Intrinsic (genetic) and extrinsic (pathogens, lifestyle).
3. Infectious Diseases
- Cause: Pathogens (bacteria, viruses, fungi, protozoa).
- Spread: Air, water, food, vectors, contact.
- Examples: TB (bacteria), malaria (protozoa).
4. Non-Infectious Diseases
- Cause: Lifestyle, genetics, deficiencies (e.g., cancer, scurvy).
- Non-communicable: Not spread person-to-person.
5. Prevention
- Personal Hygiene: Handwashing, clean water.
- Public Health: Vaccination, sanitation.
- Treatment: Antibiotics (bacteria), antivirals (viruses).
These notes summarize the chapter—use them for the Q&As!
In-Text Questions and Answers: Page 187
Question 1: Explain in detail what is meant by health, including its components and how they contribute to overall well-being, with examples from daily life.
Answer:
Health is defined as a state of complete physical, mental, and social well-being, beyond merely being free of disease or infirmity, as per the World Health Organization. It comprises three key components. Physical well-being involves a body functioning optimally—organs working, energy levels high, and no pain or fatigue. For example, eating a balanced diet with fruits and proteins keeps muscles strong and prevents illness like fatigue from anemia. Mental well-being means emotional stability and clarity—handling stress or sadness effectively. A student managing exam pressure with relaxation techniques (e.g., deep breathing) maintains mental health, avoiding anxiety.
Social well-being reflects healthy relationships and community ties—like a teenager thriving with supportive friends, reducing isolation. These components interlink: poor physical health (e.g., chronic cough) can strain mental peace, while social support (e.g., family care during flu) aids recovery. Daily examples include exercising to boost energy, talking to a friend to relieve stress, or washing hands to avoid germs—all enhancing overall well-being by nurturing body, mind, and social bonds holistically.
Question 2: Discuss comprehensively why maintaining good health is considered a community responsibility, including the role of public health measures and examples of their impact.
Answer:
Maintaining good health is a community responsibility because individual well-being depends on collective efforts to control disease spread and ensure a safe environment, facilitated by public health measures. Diseases, especially infectious ones like cholera, don’t respect boundaries—contaminated water in one home can sicken a neighborhood if sanitation fails. Public health steps like clean water supply, waste disposal, and vaccination programs protect everyone. For instance, smallpox eradication succeeded globally through mass vaccination, showing how community action eliminates threats no single person could tackle alone.
Sewage systems prevent typhoid by stopping fecal contamination—without this, even hygienic individuals fall ill from shared water sources. Mosquito control (e.g., spraying for malaria) reduces vector-borne diseases, benefiting all, not just those with nets. These measures require cooperation—taxes fund infrastructure, compliance ensures efficacy. A lone person eating well can’t avoid flu in an unvaccinated community. Thus, health’s communal nature demands joint responsibility, with public initiatives creating a ripple effect, enhancing life quality across populations, as seen in reduced polio cases through collective immunization.
Question 3: Analyze extensively how personal hygiene contributes to preventing diseases, including specific practices and their effects on pathogen transmission.
Answer:
Personal hygiene prevents diseases by reducing pathogen exposure and transmission, acting as a first line of defense against infections. Pathogens—bacteria, viruses, fungi—thrive on dirty hands, unwashed food, or unclean bodies, entering via mouth, nose, or cuts. Key practices include handwashing with soap, which removes germs like E. coli after touching contaminated surfaces (e.g., a doorknob), cutting diarrhea risk by disrupting fecal-oral routes. Bathing eliminates sweat and dirt where bacteria like Staphylococcus breed, preventing skin infections. Brushing teeth twice daily clears plaque and food bits, stopping oral bacteria from causing cavities or gum disease.
Washing vegetables removes Salmonella from soil or handling, blocking foodborne illness. These habits break transmission chains—unwashed hands after a sneeze spread cold viruses, but soap halts this. Effects are clear: studies show handwashing reduces respiratory infections by 20%. In daily life, a child washing hands before eating avoids stomach bugs, while a cook cleaning knives prevents cross-contamination. Hygiene thus curbs pathogen entry and spread, safeguarding health through simple, proactive steps.
In-Text Questions and Answers: Page 190
Question 1: Provide a thorough explanation of the difference between infectious and non-infectious diseases, including their causes, examples, and how they impact individuals differently.
Answer:
Infectious and non-infectious diseases differ fundamentally in causes, transmission, and individual impact. Infectious diseases are caused by pathogens—living agents like bacteria (e.g., tuberculosis), viruses (e.g., influenza), fungi (e.g., ringworm), or protozoa (e.g., malaria)—spreading via air, water, food, vectors, or contact. TB, for instance, travels through coughed droplets, infecting lungs and causing cough or fever. Non-infectious diseases stem from internal or lifestyle factors—genetics (e.g., sickle cell anemia), deficiencies (e.g., scurvy from low vitamin C), or habits (e.g., heart disease from smoking)—and aren’t contagious.
Scurvy weakens gums and joints but stays with the individual. Impact-wise, infectious diseases like measles can spread rapidly, affecting communities (e.g., unvaccinated schools), with acute symptoms (fever, rash) treatable by antibiotics or vaccines. Non-infectious diseases like diabetes are chronic, managed not cured (insulin shots), affecting one person long-term without spreading. A flu patient recovers quickly but risks others; a diabetic faces lifelong diet control alone. This distinction shapes prevention—vaccines for infections, lifestyle changes for non-infectious—highlighting varied health challenges.
Question 2: Elaborate in detail on how vectors contribute to the spread of diseases, including specific examples and the mechanisms involved.
Answer:
Vectors contribute to disease spread by carrying pathogens from infected hosts to healthy individuals, acting as living transporters without being diseased themselves. These are usually insects—mosquitoes, flies, ticks—whose bites or contact transmit microbes. For example, female Anopheles mosquitoes spread malaria: they bite an infected person, ingesting Plasmodium protozoa with blood. Inside the mosquito, Plasmodium multiplies, then migrates to salivary glands. Biting a healthy person injects these parasites into their bloodstream, causing fever and chills. Similarly, Aedes mosquitoes transmit dengue virus—biting spreads it directly into blood, leading to fever and joint pain.
Houseflies carry typhoid bacteria (Salmonella) on legs or bodies from feces to food, infecting eaters via ingestion. Ticks spread Lyme disease by transferring Borrelia bacteria during prolonged bites, causing rashes and fatigue. Mechanisms involve pathogen survival in vectors (e.g., mosquito saliva) and delivery via biting or contamination. Vectors amplify spread in warm, wet areas—malaria thrives in tropics—making control (e.g., nets, sprays) vital to break these biological bridges of infection.
Exercise Questions and Answers: Page 196
Question 1: A person has a persistent cough and fever for weeks. Analyze in detail whether this is likely an acute or chronic condition, including reasoning and possible causes.
Answer:
A persistent cough and fever lasting weeks suggest a chronic condition, as acute diseases resolve quickly (days), while chronic ones persist or recur over time. Acute illnesses like a common cold cause cough and fever but subside within a week via rest or mild treatment—here, duration exceeds that. Chronic possibilities include tuberculosis (TB), a bacterial infection (Mycobacterium tuberculosis) spread by air, causing prolonged cough (often bloody), fever, and weight loss, worsening without antibiotics. Another cause could be chronic bronchitis, from smoking or pollution, with ongoing airway inflammation triggering cough and low-grade fever.
Reasoning: acute infections (e.g., flu) don’t linger weeks unless complications arise, rare without other signs (e.g., pneumonia’s rapid severity). TB fits endemic areas; bronchitis suits lifestyle factors. Chronicity implies a deeper issue—immune response or pathogen persistence—needing medical diagnosis (e.g., chest X-ray) beyond acute self-healing, distinguishing it by time and intensity.
Question 2: State two conditions essential for good health and explain thoroughly how their absence affects an individual’s well-being, with examples.
Answer:
Two conditions essential for good health are balanced nutrition and clean water.
- Balanced Nutrition: Provides proteins, vitamins, carbs for body function. Absence leads to deficiencies—e.g., lack of vitamin C causes scurvy (bleeding gums, fatigue), as sailors historically suffered without fruit. Malnutrition weakens immunity, increasing infection risk (e.g., colds), and stunts growth in kids.
- Clean Water: Hydrates and prevents pathogen intake. Without it, dehydration fatigues muscles and brain (e.g., a worker faints in heat), while contaminated water spreads cholera (diarrhea, death), as in polluted slums. Both absences disrupt physical well-being, raise disease vulnerability, and strain mental health via stress or weakness, showing their foundational role.
Class 9 Science Chapter 13: Why Do We Fall Ill explores health and disease for your 2025 CBSE exams. With these notes and Q&As, you’re ready to excel. Check NCERT solutions for more, and comment your questions—we’re here!
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