NEET Biology Class 9 Chapter 4 Why Do We Fall ill Notes

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Why Do We Fall Ill?

  • Food is the basic necessity of life. We all know that a regular supply of food is essential for human beings in order to keep fit and carry on all life processes. Thus, proper food is, therefore, a basic necessity for the proper functioning of cells, their tissues, and organs.
  • Anything that disturbs the proper functioning of cells, tissues, and organs will result in the lack of proper activity of the body or an unhealthy body. Thus, health is considered to be the state of perfect functioning of body and mind, unhindered by diseases. So what do you understand by a healthy individual? An individual free of disease is termed healthy.
  • However, health has a different meaning in different contexts. For example, for a grandfather, the ability to go out for exercise is good health. If he is unable to do so, it is considered his health is not good. Similarly, a youngster is healthy, if he can run, jump, and play. A student who remains active and attentive in class is said to have a healthy attitude.
  • Therefore, good health is a healthy body with a healthy mind and a healthy attitude.
  • Health does not simply mean “absence of disease” or “physical finess”. It could be defined as a state of complete physical, social, and mental well-being.

Read And Learn More: NEET Class 9 Biology Notes

Importance of Good Heath:

  1. It increases our efficiency in doing work. This increases productivity and brings economic prosperity.
  2. It makes the man happy and cheerful.
  3. A healthy person can give proper attention to others in the family.
  4. It gives a condition for our purposeful existence in this world.
  5. It also increases the longevity of people and reduces infant and maternal mortality.

Personal And Community Issues In Relation To Health:

Good health, which means a state of physical, social, and mental well-being, implies that:

  • Health cannot be achieved by individuals alone.
  • Health depends upon the surroundings or one’s environment.

The environment can be:

  1. Physical related to heat, storms, cyclones, floods, etc.
  2. Social is related to the society in which one lives. The social environment controls not only social health but also the physical health of the individual through public health services.

There are certain factors that have an adverse effect on human health:

Let us discuss some of these factors:

  1. Public health services: Public health services ensure a clean environment around our surroundings and protect the public from outbreaks of diseases. It ensures the removal of garbage, drainage and sewage services, proper drinking water, pest control, vaccination, and other health care services. If these services are faulty, the health of individuals is adversely affected despite taking the best-balanced food and keeping the best personal hygiene. For instance, if garbage is not collected and drains are not cleaned, pests and vectors might breed in the area resulting in the spread of disease.
  2. Economic status of an individual: Good economic condition and job are essential for maintaining good health of an individual. This enables an individual to consume a wholesome balanced diet, which is very much required for keeping everyone in the family healthy.
  3. Social equality and Harmony: Good health is required for participating in one another’s joys and sorrows, helping others, and receiving help at the time of need. This would make everyone in the community happy and healthy.
  4. Personal Hygiene: It includes personal cleanliness such as cleaning teeth, taking baths regularly, taking care of eyes, breathing through the nose, wearing cleaned clothes, etc. Besides personal hygiene, timely vaccination and timely protection from vectors of disease are important for keeping an individual and community healthy.

Disease (Dis-Without, Ease-Comfort)

  • You all must, at one time or another in your life, have suffered from fever, body aches, cold, cough, or vomiting. You must have felt uncomfortable. Such a condition where you feel uncomfortable or uneasy is known as a disease.
  • It is just the opposite of health. It is defined as the malfunctioning of body organs due to one reason or another.
  • So, what is a disease? A Disease can be defined as any condition that may lead to discomfort, distress, health problems, or death of the affected person. It may be due to defective heredity, inappropriate diet, disturbed metabolism or pathogenic attack.
  • A person is said to be disease-free if there is no discomfort or derangement of the functioning of the body.

Difference between a healthy and a disease-free state of the human body:

  • The state of not having any disease is not the same as being healthy. Good health is the ability of an individual to realize his or her full potential. For example, if an athlete is tired after running about 100 m, then he cannot be called a diseased person.
  • However, he is not healthy either. Therefore, it can be concluded that one can have poor health without having any identifiable disease.

NEET Biology Class 9 Why Do We Fall Ill Difference between a healthy and a disease-free state of human body

Diseases and Their Causes:

  • Disease means uncomfortable. Disruption in the functioning of any tissue, organ or organ system will cause discomfort or disease.
  • The diseases are diagnosed with the help of symptoms or signs.

Symptoms: Symptoms are evidence of the presence of diseases.

  • The malfunctioning of organs produces external symptoms of diseases. It indicates that there is something wrong with the body.
  • It can be in the form of structural and functional changes in the body or body part. For example, cold, cough, loose motions, pain in the abdomen, headache, fever etc are symptoms of certain diseases.
  • However, symptoms do not give any exact cause of the disease. For example, headaches can be due to a number of diseases, like typhoid, jaundice or malaria. Sometimes, it is simply due to the day’s heavy work or exam stress.

Sign: Signs are definite indications of the disease. It is on the basis of the symptoms that the physician searches for definite clues or signs of the disease and sometimes goes for laboratory tests to confirm the disease.

Difference between Symptoms and Signs:

NEET Biology Class 9 Why Do We Fall Ill Difference between Symptoms and Signs

Causes of Diseases:

Causes of diseases are basically agents and factors that produce diseases in the body. Although there can be a number of causes for a disease, they can be broadly divided into immediate causes and contributory causes.

  1. Immediate causes: It is the primary cause of the disease. Hence, it is also known as first level of cause. It includes external agents like micro-organisms. Organisms like virus, bacteria, and other micro-organisms can cause diseases in a person. Suppose an individual is suffering from diarrhea. The immediate or the first level of cause is the pathogen, which may be viral or bacterial infection.
  2. Contributory causes: Even though a virus can be the immediate cause of a disease, other associated causes might allow the entry of the virus into the body. These causes are known as contributory causes.

These include the following conditions:

  1. Unhealthy condition: Infectious agents like virus and bacteria enter the body through contaminated food or water. Thus, the consumption of contaminated food or water can be another cause of disease.
  2. Improper public service: The lack of proper public service is the main reason for the lack of clean drinking water and food.
  3. Poverty: Lack of nourishment can also lead to the occurrence of diseases in a person. There are a number of children consuming contaminated food or water. Then, why do only some children get diarrhea while others remain disease-free? It is because, a healthy body or a well-nourished body is less likely to catch a disease when exposed to disease-causing agents, whereas a poorly nourished body will easily become diseased.
  4. Genetic differences: A child might have a genetic program due to which it can catch diarrhoea on immediate exposure. Do people get diseases only for a short period or do people suffer from a particular disease throughout their lifetime? On the basis of duration, a disease can be classified into two broad categories:
    1. Acute diseases: Diseases that last for only a short period of time are known as acute diseases. However, they spread rapidly in the body showing intense symptoms. They can be mild, severe, or fatal. Examples are cold, cough, inflenza, typhoid etc.
    2. Chronic diseases: Diseases that last for a longer period are called chronic diseases. They can also be mild, severe, or fatal. They do not spread rapidly; instead, they develop slowly over a period of time. Examples are tuberculosis, cancer, diabetes, kidney stones etc.

Difference between acute and chronic disease:

NEET Biology Class 9 Why Do We Fall Ill Difference between acute and chronic disease

Types of Diseases:

Diseases are broadly classified into two categories:

  1. Congenital Diseases: These are diseases that have been present since birth. For instance, a hole in the heart of an infant. They are caused by some genetic abnormalities or metabolic disorders or malfunctioning of an organ.
  2. Acquired Diseases: These are diseases that may occur after birth during one’s lifetime. Based on their ability or inability to spread from one individual to another, acquired diseases are of two types:
    1. Infectious or Communicable diseases: The diseases that can be transmitted from a diseased person to a healthy person by means of infectious agents are known as infectious or communicable diseases. For example, tuberculosis, measles, malaria etc.
    2. Noninfectious or Non-communicable diseases: The diseases that cannot be transmitted from an affected individual to a healthy person are known as non-infectious or non-communicable diseases. For example, high blood pressure, Cancer, Allergy, Obesity, etc.

Non-infectious diseases are not caused by any pathogen or living organism. They are mostly due to internal or intrinsic non-infectious causes. For example, High blood pressure is caused due to lack of exercise or excessive weight. Similarly, Cancer is caused due to genetic abnormalities.

Difference between Infectious (Communicable) and Non-infectious (Non-communicable) diseases:

NEET Biology Class 9 Why Do We Fall Ill Difference between Infectious (Communicable) and Non-infectious (Non-communicable) diseases

Non-infectious diseases are further classified as:

  1. Degenerative diseases: These diseases are caused by the malfunction of some vital organs of the body. E.g. heart failure.
  2. Deficiency diseases: These are caused due to nutritional deficiency such as that of minerals or vitamins in the diet. E.g. anemia (due to deficiency of B12), Beri- beri (due to deficiency of vitamin B).
  3. Allergies: These are caused due to hypersensitivity of the body to certain foreign substances.
  4. Cancer: This is an abnormal, uncontrolled, and unwanted growth of cells. E.g. Breast cancer, leukemia

NEET Biology Class 9 Why Do We Fall Ill Classifiation of human diseases

Agents Causing Diseases:

By now, you have learned that, communicable diseases are those diseases that can be transmitted from one person to another. But have you ever thought how a disease is transmitted from one person to another? Anyways, before answering this question, let us first understand about various agents that cause disease.

Agents that cause diseases are known as infectious agents. The various infectious agents are bacteria, viruses, protozoan, helminths and fungi.

  1. Bacteria: Bacteria are unicellular organisms. They are larger than viruses. Only some bacteria cause diseases while others are useful in nature. Whooping cough, typhoid, cholera, anthrax, etc. are some human diseases caused by bacteria.
  2. Fungi: Fungi are plant-like organisms, which are
    heterotrophic in nature. They lack chlorophyll. Their cells have cell walls. Athlete’s foot, ringworm, etc. are some human diseases caused by fungi.
  3. Protozoa: They are simple, primitive unicellular organisms, which include Amoeba, Trypanosoma, and Leishmania. They are often found in water as they require moisture for survival. Hence, they cause diseases through contaminated water. Amoebiasis, kala-azar, malaria, African sleeping sickness, etc. are some diseases caused by protozoa.
  4. Worms: Worms are parasites, which infect the intestines of human beings and animals. Roundworms, pinworms, hookworms, and tapeworms are some examples of disease-causing worms. Diarrhea, anemia, liver rot, etc. are some diseases caused by worms

If there is bacterial infection along with the common cold, the antibiotic will prove to be effective, but only against the bacterial part of an infection.

Question 1. List down at least three points of precautions that need to be taken while using antibiotics.
Answer:

  1. Always take antibiotics on the advice of a well-qualified doctor.
  2. The course of antibiotics should be completed as per the prescription given by the doctor.
  3. Always take antibiotics in the right amount and at the right time. An inappropriate dose of antibiotic makes it ineffective. Also, its excessive consumption may kill the useful bacteria present in our bodies.

Question 2. Why it is advised to take an appropriate dose of antibiotics?
Answer:

It is advised to take the appropriate dose of antibiotics because under dose of antibiotic makes it ineffective, while its excessive consumption may kill the useful bacteria present in our body

Let us now explore the various modes of transmission of diseases:

Modes of Transmission of Diseases:

Diseases can spread through the following means:

  1. By air: You must have observed that when you sit near a person infected with a cold, you catch it too? Can you explain why? It happens because the virus that causes cold can reach your body through air. Hence, the common cold is an airborne disease.
  2. A number of disease-causing microbes spread through the air. The pathogens may reach the body through little droplets throughout when an infected person sneezes or coughs. A healthy individual standing nearby can inhale these droplets, causing infection in that person.
    Diseases spreading through the air are the common cold, Pneumonia, Tuberculosis, Diphtheria etc. Airborne diseases are more common in crowded areas as well as in poorly ventilated rooms.
  3. By water and food: Some diseases are transmitted when excretions from an infected person containing causal microorganisms get mixed with drinking water. Consumption of this contaminated water leads to the spread of diseases.
    In addition, when food is prepared using this contaminated water, it can lead to food-borne diseases. Some water and food-borne diseases are cholera, typhoid, hepatitis A, Jaundice, Diarrhoea etc.
  4. Direct physical contact: Sexual act involves close contact between two people, which leads to the transfer of diseases such as syphilis, gonorrhea, AIDS, etc. These diseases are known as sexually transmitted diseases. However, casual physical contact such as handshake, hugging, and kissing do not lead to the transfer of these diseases.
    Diseases that spread through sexual contact are AIDS, Syphilis, and gonorrhea.
  5. Blood-to-blood contact: This type of contact is established through blood transfusion or during pregnancy (between mother and baby) and through breastfeeding. A disease that spreads through blood is AIDS.
  6. Animals or vector-borne diseases: Organisms that do not cause diseases themselves, but spread infection by transferring disease-causing microorganisms from an infected person to others are known as vectors.

Mosquitoes are vectors of malaria. Malaria is caused by the protozoan Plasmodium. This protozoan is carried from an infected person to a healthy person by Female Anopheles mosquitoes.

  • The female Anopheles mosquito requires highly nutritious blood to lay eggs, so they feed on warm-blooded animals.
  • The female mosquito that bites an infected person can transfer the disease-causing microorganism from an infected person’s blood to a healthy person.
  • Another common vector is useful. Houseflies carry the causative organisms of cholera on their legs and mouth parts from the feces and sputum of infected persons to food and drinks and contaminate them. When this contaminated food is taken by a healthy person, he gets the infection.

Diseases that spread through vectors are: Malaria, Rabies

NEET Biology Class 9 Why Do We Fall Ill Modes of transmission of disease

Organ-Specific And Tissue-Specific Manifestations Of Disease-Causing Microbes

  • We know that disease-causing microorganisms can enter our body through various agencies such as air, water, food, or some animals.
  • But what happens when a microbe enters our body? Does our body show any reaction to the entry of a foreign microorganism? Let us explore.

Effects of microbes on the body:

It is believed that microbes affect specific organs depending on the site of their entry.

For example:

  • If a microbe enters our body through the nose, then it is most likely to reach the lungs. The bacterium that causes tuberculosis enters via the nose and affects the lungs.
  • If a microbe enters through the mouth, then they either stay in the gut lining (as in typhoid) or affect the liver (as in jaundice).
  • However, this may not always be true.
  • The AIDS virus enters the body through sexual contact and then spreads to lymph nodes all over the body.
  • Similarly, malaria-causing Plasmodium enters through blood, goes to the liver to multiply, and then passes into the red blood cells of the body.

Thus, signs and symptoms of a disease depend upon the affected tissue or organ.

Tissue or organ-specific effects:

  • If the lungs are the target, then the symptoms will be coughing and breathlessness.
  • If the liver is the target, then it will result in jaundice.
  • If the brain is the target, then it will result in fis, vomiting, headache, etc.

In addition to these tissue-specific effects, there will be some common effects, which can be divided into two types:

  1. Local effects: They include swelling, pain, joint stiffness, joint pain, etc. They occur only at the site of infection.
  2. General effects: They include fever, chills, headaches, fatigue, loss of appetite, etc. They occur in the body.

Let us now discuss, how these effects arise in the body.

  • Most of the mentioned effects depend upon the immune system of the body. An active immune system directs many cells to the site of infection to kill the pathogens or disease-causing microorganisms.
  • This response of the immune system is known as an inflmmatory response.
  • The general and local effects are caused due to inflmmation.

Inflammation:

Inflammation is the process by which the body’s immune system (white blood cells and some chemicals) show response to protect the body from infection. The immune system fights off these foreign substances by triggering general and local effects.

What happens when the immune system is damaged? If the immune system is damaged, then the body will not be able to fight infections. Then, any minor disease can prove fatal.

There are certain conditions where the immune system is unable to protect the body.

They are as follows:

  • Severe diseases: In HIV infection, the virus damages the immune system. Therefore, the body is not able to fight minor infections such as cold and cough. In such cases, a minor cold can become pneumonia. Similarly, a minor gut infection can lead to diarrhea. Thus, these minor infections can kill an HIV-AIDS patient.
  • Number of microbes: Severity of a disease also depends upon the number of microbes in the body. If the number of microbes is small, then the disease may be minor. However, if the number of microbes is large, then the disease can be life-threatening.

Principles of Treatment:

There are two ways to treat an infectious disease.

These are:

  1. By reducing the effect of disease without killing the infectious agents. This could be done by two methods:
    1. By taking medicines to reduce the fever or pain or to stop loose motion as the case may be.
    2. By taking complete bed rest. Bed rest is advised to conserve energy and to make the same available for healing.
  2. By eliminating or killing the cause of the disease. For complete recovery from the disease, it is essential that antibiotics specific to the disease-causing micro-organisms are taken. Antibiotics are drugs which can block the biochemical life processes of bacteria without harming human cells

Antibiotics:

  • Antibiotics are chemicals produced by micro-organisms mainly bacteria and viruses, to kill other disease-causing micro-organisms.
  • These medicines either kill or stop the growth of disease-causing microorganisms.
  • The first antibiotic was penicillin, which was developed in 1940s in response to the need to treat soldiers in the Second World War.
  • There are now about 50 to 100 commercially available antibiotics. Tetracycline, Streptomycin and Erythromycin are some other examples of antibiotics.

Antibiotics are characterized by their range of effectiveness and their mode of action against the pathogens.

  • Broad-spectrum antibiotics kill a wide range of bacteria.
  • Narrow-spectrum antibiotics are effective against only a few types of bacteria. To kill a specific pathogen, you have to use narrow spectrum antibiotics which are specific for the disease.

Antibiotics interfere with the growth or metabolism of the pathogen in a variety of ways. For example,

  1. The antibiotic, penicillin inhibits the enzymes that are involved in the formation of bacterial cell wall. As a result of weakened cell wall, the immune cells such as white blood cells enter into bacterial cell and causes cell lysis. Cell lysis is the process of destruction of cells such as blood cell and bacteria.
  2. Streptomycin binds to bacterial ribosomes, preventing protein synthesis and enzyme synthesis. The lack of protein affects bacterial function and result in its death. Streptomycin does not interfere with the synthesis of proteins in the cells of the patient taking the drug.

Principles of Preventing Diseases:

As we all know, prevention is always better than cure. Every infection brings about misery not only to the affected person but also to a number of others connected to the same.

Therefore, it is necessary to prevent the infectious diseases. A disease can be prevented by two ways:

1. General Ways of Preventing Infectious Diseases:

These are:

  1. Preventing the spread of a disease:
    1. To prevent airborne diseases
      1. Stay away from the diseased person.
      2. Wear a mask when you need to contact a diseased person.
      3. Cover your mouth and nose while coughing or sneezing to prevent the spread of the disease.
    2. To prevent waterborne diseases:
      1. Ensure proper disposal of sewage.
      2. Ensure safe drinking water supply.
    3. To prevent vector-borne diseases:
      1. Provide a clean environment, which helps in preventing vectors like mosquitoes from breeding.
      2. Availability of proper nutrition. If proper and suffiient nutrition is not available, the immune system of the body will not function properly.

Immune System:

  • How does immune system help in fighting against diseases? The immune system develops strength in the body to fight off microbes.
  • It is made up of special cells, proteins, and organs which protect the body against micro-organisms.
  • White blood cells are a part of the immune system. These cells destroy disease-causing micro-organisms.
  • They are produced in the thymus, bone marrow, and spleen (lymphoid organs).
  • These white blood cells or leukocytes defend the body against antigens.
  • Antigens are foreign substances (e.g. bacteria, virus) that invade our body.
  • Antigens trigger the production of antibodies by the immune system.
  • Antibodies are body’s defensive cells that fight against several infectious foreign substances i.e. antigens.
  • Each type of antibodies is specific to a particular antigen and makes it harmless.

Reaction between antibody and antigen:

It involves three main steps:

  • The lymphocytes recognize antigens on the surface of bacteria as foreign and produce antibodies against them.
  • Antibodies and antigens form immune complexes on surface of bacteria, making the bacteria clump together.
  • This stimulates the phagocytosis (engulfment) of bacteria, which are then destroyed inside the vacuole.

Immunity:

Immunity is Defined as protection of the body against an infectious (foreign) agent. The immunity developed by the body against a disease after the vaccination is divided into two types:

  • Temporary Immunity: It is the immunity developed for a short period of time.
    Example: Cholera vaccine, where immunity lasts for about 6 months.
  • Permanent Immunity: It is immunity that last throughout life.
    Example: Small Pox vaccine where immunity lasts throughout life

2. Specific ways of Preventing Diseases: It refers to the defense provided by the immune system of a person.

You must have observed that if you are suffering from cold and cough, others around you try to keep away? This is because people around may get exposed to infection. But at the same time, sometimes, it is observed that all of them do not catch infection. Have you ever thought why it happens so? This is because our bodies have an immune system that protects us from various microorganisms.

Immunity is the ability of body to protect itself from infection and diseases. The immune response varies from person to person. This is why; some people are more sensitive or prone to infection than other. For example, if a child has suffered from smallpox once, then there is almost no chance of him suffering from it again. This happens because, when the immune system of the body encounters a virus or an antigen for the first time, it reacts against it and remembers it.

Therefore, when the virus enters the body for a second time, the immune system reacts more strongly to prevent the chances of suffering from the disease again. Therefore, it can be concluded that if we infect the body of a person with something that mimics the microbe, then the immune system will remember it and will prevent the actual disease-causing microbe from causing any disease

Vaccination

  • You must have seen on television or read in the newspapers about Pulse Polio Day when children between the age group of 0-5 years are given the polio vaccine. So, what is a vaccine? What is meant by the term vaccination? Let us explore.
  • Vaccination may be Defined as the protection of the body from communicable diseases by the administration of some agents that mimic the microbe. The agent can be a suspension of killed or attenuated microbes or a substance that mimics the disease-causing microbes. This is known as a vaccine.
  • Vaccines protect humans and other animals from several diseases such as Cholera, Typhoid, Tuberculosis, Hepatitis, Chicken pox, Measles, Polio, and Small pox.

In vaccination, a vaccine containing an antigen is injected inside the body of an organism.

  • Antigens once inside the body, stimulate the body’s defensive mechanism to produce antibodies.
  • Antibodies arse body’s defensive cells that fight against several infectious foreign substances mostly germs. This is the primary immune response and thereby lymphocytes are generated.
  • When the vaccinated person is attacked by the same pathogen, the memory cells recognise the antigen quickly and control the invaders by producing a larger number of lymphocytes and antibodies.
  • These fight against the antigen, thus protecting the organism against the disease

NEET Biology Class 9 Why Do We Fall Ill Disease causing pathogens

NEET Biology Class 9 Why Do We Fall Ill vaccination

  • Vaccination is based on specific ways of defense provided by the immune system of a person. For example, if a child has suffered from smallpox once, then there is almost no chance of him/her suffering from it again. This happens because when the immune system of the body encounters a virus for the first time, it reacts against it and remembers it.
  • Therefore, when smallpox virus attacks the body for a second time, the immune system reacts strongly to prevent the chances of suffering from the disease again.
  • Therefore, it can be concluded that if we infect the body of a person with something that mimics the microbe, then the immune system will remember it, and prevent the actual disease-causing microbe from causing any disease. It forms the basis of vaccination.
  • Vaccines are available against many diseases like tetanus, polio, measles, hepatitis B, whooping cough, yellow fever etc.

Question 1. What are the vaccinations that you have received?
Answer: Hepatitis B, DTP, polio, chickenpox, and MMR are some of the vaccines that you must have received.

Question 2. While going abroad, Sonia was asked to get vaccinated against certain diseases. Why?
Answer:

  • An individual, as Sonia in this case, maybe a carrier of some disease and may take that particular disease to a foreign country.
  • Therefore, all visitors to a foreign country are vaccinated against the disease which is not prevalent in that country.
  • Diseases are caused by different causative agents. These agents are known as pathogens. Hence, the pathogen is Defined as living organisms that cause disease.
  • Let us discuss various types of diseases, their mode of transmission and preventive measures.

Viral Diseases

1. Jaundice/Hepatitis:

Pathogen: Hepatitis virus.

Mode of transmission: Hepatitis A is transmitted mostly by contaminated food and water while hepatitis B is transmitted by contact with infected body secretions.

Symptoms:

  1. Fever and loss of appetite
  2. Nausea and vomiting
  3. Yellowness of skin
  4. Itching of skin due to bile pigments
  5. Urine deep yellow in colour
  6. Enlarged liver
  7. Headache and joint pains

Prevention and Cure:

  1. Adequate bed rest.
  2. Carbohydrate-rich diet should be given to the patients. Consumption of protein and fat should be limited.
  3. Eating hygienic food and drinking disinfected water.

2. Rabies (Also known as hydrophobia):

Pathogen: Rabies virus

Mode of transmission: Biting of rabid dog or cat.

Symptoms:

  1. Severe headache and high fever.
  2. Painful contraction of muscles of throat and chest.
  3. Choking feelings and fear of death.

Prevention and cure:

  1. Compulsory immunization of pet dogs and cats with anti-rabies vaccine.
  2. Killing of rabid animals if it shows excessive salivation and tries to seek isolation.
  3. It can be treated by Pasteur treatment in which 14 injections are given one by one on each day. However, these days, fie dose of anti-rabies vaccine are given at an interval of 0. 3, 7, 14 and 30th day of a dog bite.

3. Polio:

Pathogen: Poliovirus

Mode of transmission: Through food or water contaminated with stool and urine of patients.

  • The polio virus enters the body through food and water and reaches the intestine and from there, it enters the central nervous system (brain and spinal cord) via bloodstream and lymphatic systems.
  • In central nervous system, the virus destroys the motor nerve cells of spinal cord that is responsible for the muscular control. Therefore, the muscles of a polio-infected person become unable to carry out the normal functions.

Symptoms:

  • Headache and fever followed by loss of head support.
  • As the virus damages the brain and nerves of the spinal cord, the legs become paralyzed.
  • Stiffness of neck and convulsions.

Prevention and Cure:

  • Polio vaccine drops are given to children at certain intervals.
  • The Pulse Polio program is a program organized in our country to give polio vaccines to children. It was launched in 1995-1996 to cover all children below the age of 3 years.

4. Influenza (commonly known as flu): Compared to the common cold, influenza is a more severe illness.

Pathogen: Myxivirus influenza (influenza virus), which attacks our body’s cells.

Mode of transmission: Through air.

Symptoms:

  1. Fever
  2. Respiratory tract infection symptoms such as cough, sore throat, running nose, headache, pain in muscles, and fatigue.

Prevention and Cure:

  1. By annual influenza vaccination.
  2. Person suffering from inflenza should drink plenty of water.
  3. Consult a doctor immediately for treatment.

Influenza Virus:

There are many strains of influenza virus. The virus mutates all the time and new variations (strains) arise. This constant change enables the virus to evade the immune system of its host.

Unfortunately, immunity against one strain (which is conferred by exposure or immunization) does not protect against other strains. A person infected with influenza virus develops antibodies against that virus; as the virus changes, the antibodies against the virus do not recognize the changed virus, and influenza can recur, caused by the changed or mutated virus.

5. Dengue:

Pathogen: Virus

Symptoms:

  1. Sudden onset of high fever, which may last for 4-5 days.
  2. Severe headache mostly in the forehead.
  3. Pain in muscles, and joints. Body aches.
  4. Pain behind the eyes which worsens with eye movement.
  5. Vomiting or nausea.

Prevention and Cure:

  1. Avoid water stagnation for more than 72 hours so that the mosquitoes do not breed there.
  2. Prevent mosquito breeding in stored water bodies, like ponds, wells etc,
  3. Destroy discarded objects like old tires, bottles, etc. as they collect and store rainwater.
  4. Use mosquito repellents and wear long-sleeved clothes to curtail exposure.
  5. Use mosquito nets, also during the daytime.
  6. Avoid outdoor activities during dawn or dusk when these mosquitoes are most active.

Dengue:

Dengue is of two types:

  1. Dengue fever: It is characterized by an onset of sudden high fever, severe headache, and pain behind the eyes and in the muscles and joints.
  2. Dengue hemorrhagic fever: It is an acute infectious viral disease. It is an advanced stage of dengue fever. It is characterized by fever during the initial phase and other symptoms like headache, pain in the eye, joint pain, and muscle pain, followed by signs of bleeding, red tiny spots on the skin, and bleeding from the nose and gums.

How does Dengue spread?

Dengue spreads through the bite of an infected Aedes aegypti mosquito. The transmission of the disease occurs when a mosquito bites an infected person and subsequently bites a healthy person. In doing so, it transmits blood containing the virus to the healthy person and the person becomes infected with dengue. The first symptoms of the disease occur about 5 to 7 days after the infected bite.

Aedes mosquito rests indoors, in closets and other dark places, and is active during the daytime. Outside, it rests where it is cool and shaded. The female mosquito lays her eggs in stagnant water containers such as coolers, tires, empty buckets etc., in and around homes, and other areas in towns or villages. These eggs become adults in about 10 days.

Question 1. Wearing socks and full sleeves at night will prevent the attack from dengue. Do you agree with this statement?
Answer:

No, Dengue is caused by the biting of an Aedes mosquito which is active during the time only.

6. Chickenpox:

Pathogen: Varicella virus

Modes of transmission: By contact

Symptoms:

  1. Fever, headache, and loss of appetite.
  2. Dark red-coloured rash on the back and chest which spreads on the whole body. Later, rashes change into vesicles. After few days these vesicles start drying up and scabs (crusts) are formed. These scabs start falling.

Prevention and Cure:

There is no vaccine against chicken pox as yet.

But precautions must be taken as follows:

  1. The patient should be kept in isolation.
  2. Clothing, utensils, etc. used by the patient should be sterilized.
  3. Fallen scabs should be collected and burnt.

7. AIDS (Acquired Immuno Deficiency Syndrome): The word “immune deficiency” signifies that the immune system becomes very weak. It is a disorder of the cell-mediated immune system of the body.

Lymphocytes are the main cells of the immune system i.e. T-lymphocytes and B-lymphocytes. ‘Helper T’ lymphocytes play a great role in regulating the immune system. Damages or destruction of ‘Helper’ lymphocytes lead to the development of a cellular immune deficiency which makes the patient susceptible to a wide variety of infections.

Pathogen: HIV (Human Immunodeficiency Virus)

Mode of transmission:

  1. Sexual contact with the affected person. In India, the most common route of HIV transmission is through unprotected sex.
  2. Using the same syringe as that of the affected person.
  3. Transfusion of blood contaminated with human immune deficiency virus.
  4. From mother to newborn baby during pregnancy or during birth.

Symptoms:

  1. A type of lung disease develops (tuberculosis).
  2. Skin cancer may be observed.
  3. Nerves are affected.
  4. The brain gets badly damaged with the loss of memory, loss of ability to speak and to think.
  5. The number of platelets (thrombocytes) becomes less which may cause hemorrhage.
  6. In severe cases, the patient shows swollen lymph nodes, fever and loss of weight.

A full-blown (disease at its peak) AIDS patient, may die within three years.

Prevention and Cure:

No medicine or vaccine is known to be available against HIV infection. Therefore, care has to be taken through the following measures:

  1. There should not be any sexual contact with the person who has HIV infection
  2. Use a disposable syringe and needle.
  3. Before receiving blood for transfusion, one should ensure that it has been screened for HIV.
  4. Condom should always be used during intercourse.
  5. People should be educated about AIDS transmission.

Facts About Hiv Transmission:

  • HIV is a weak virus and hard to get infected with. It cannot be transmitted through air or water outside the human body.
  • A person cannot get AIDS by hugging or sneezing of an infected person, insect bites (including mosquitoes), or sharing the same comb, plates, glass, handkerchiefs, knives or cutlery.
  • A person cannot get AIDS by using public toilets, swimming pools, showers, and telephones.
  • HIV is not transmitted by being near to someone, touching someone or working with someone who is suffering from AIDS.

Question 1. Why AIDS is considered a “syndrome” and not a ‘disease’?
Answer:

A syndrome is a group of symptoms, signs, or physical or physiological disturbances that are due to a common cause. AIDS is considered as a syndrome because it is a complex of disease and symptoms that develop due to the failure of the immune system of the body. HIV that causes AIDS damages the immune system of the patient. As a result, even a small cold leads to pneumonia; a minor infection leads to severe diarrhea and blood loss and simple skin rashes develop into ulcers.

Bacterial Diseases

1. Tuberculosis:

Pathogen: Mycobacterium tuberculosis. The bacterium releases a toxin called tuberculin.

Mode of transmission: Directly by sneezing, coughing or spitting or indirectly by air-borne pathogen discharged through sputum, cough, and sneeze of an infected person.

Symptoms:

  1. Persistent fever and cough
  2. Chest pain and breathlessness
  3. Sputum containing blood
  4. Loss of weight and weakness.

Prevention and Cure:

  1. Isolation of TB patients to avoid the spread of disease.
  2. Use of handkerchief while coughing and sneezing
  3. BCG (Bacillus Calmette Guerin) vaccine provides immunity.
  4. Living rooms should be clean, neat, and airy.

2. Typhoid:

Pathogen: Salmonella typhi bacteria.

Mode of transmission: Through contaminated food and water and house flies.

Symptoms:

  1. Continuous fever, headache, and slow pulse rate.
  2. Reddish rashes appear on the upper abdomen.
  3. Diarrhea which becomes hemorrhagic (loss of blood)

Prevention and Cure:

  1. Proper sanitation and cleanliness should be maintained.
  2. Proper disposal of excreta of the patient.
  3. Antibiotics should be administered.
  4. Disinfection of water and proper cooking of food should be done.
  5. TAB-vaccine provides immunity for 3 years.

3. Cholera:

Pathogen: Vibrio cholerae (Comma shaped bacterium)

Mode of transmission: Through contaminated food and water. House fl is the carrier.

Symptoms:

  1. Acute diarrhoea
  2. Muscular cramps
  3. Loss of minerals through urine
  4. Dehydration, which can lead to the death of an individual

Prevention and Cure:

  1. Cholera vaccination should be given.
  2. Proper washing and cooking of food should be done.
  3. Electrolytes (Na, K, sugar, etc.) dissolved in water should be given to the patient to check dehydration. In market it is available as ORS (Oral Rehydration solution).
  4. Underground disposal of excreta.
  5. Proper covering of eatables to prevent contamination.

Oral Rehydration Solution (ORS):

It is an ideal solution to prevent dehydration in child. It can be prepared as follows:

  1. Take a glass of water and add
    1. Three teaspoonfuls of sugar
    2. A quarter teaspoonful of common salt.
    3. A pinch of sodium bicarbonate
    4. A few drops of lemon juice
  2. Mix the entire content well and give this solution to the patient having cholera or diarrhoea at least fie to six times a day to prevent dehydration.

NEET Biology Class 9 Why Do We Fall Ill ideal solution to prevent dehydration in child

Protozoan Diseases

1. Malaria:

Pathogen: Malarial parasite, Plasmodium

Mode of transmission: By bite of female Anopheles mosquito. Male Anopheles mosquito feed upon plant juices.

Symptoms:

  1. Headache, nausea and muscular pain
  2. Feeling of chill and shivering followed by fever which becomes normal along with sweating after some time.
  3. Patient becomes weak, exhausted and anaemic.
  4. The malaria may secondarily cause enlargement of liver and spleen.

Prevention and Cure:

  1. Wire-gauzing of doors, windows etc to check the entry of mosquitoes.
  2. Use of mosquito net and mosquito repellents.
  3. Taking care of coolers, flwer pots and uncovered water containers to prevent breeding of mosquitoes.
  4. Sprinkling of kerosene oil in ditches or other open spaces where water gets collected.
  5. All the mosquito breeding places like ponds and ditches should be destroyed or covered.
  6. Use of insect repellants to prevent mosquito bite.

2. Amoebiasis (Amoebic dysentery):

Pathogen: Entamoeba histolytica

Mode of transmission: Through contaminated food and water.

Symptoms:

  1. Formation of ulcers in intestine.
  2. Feeling of abdominal pain and nausea.
  3. Acute diarrhoea and mucus in stool.

Prevention and Cure:

  1. Proper sanitation should be maintained.
  2. Vegetables and fruits should be properly washed before eating.
  3. Antibiotics may be given to the patients.

Helminthal Diseases (Worms)

1. Filariasis:

Pathogen: Wuchereria bancrofti, fiarial worm

Mode of transmission: Biting of mosquitoes- Aedes and Culex

Symptoms:

  1. Fever
  2. Collection of endothelial cells and metabolites in the wall of lymph vessels.
  3. Swelling of legs which appear as the legs of an elephant, so this disease is also called elephantiasis

Prevention and Cure:

  1. Wire gauzing of doors, windows etc to check the entry of mosquitoes.
  2. The water collected in tanks or other articles should be properly covered to prevent the breeding of mosquitoes.
  3. A sprinkling of kerosene oil on ponds and ditches to kill the larva.

Question 1. “Precaution is always better than cure.” What precautions would you take to prove this statement?
Answer:

Precaution is always better than cure as diseases always cause some damage to the body.

Important precautions for preventing diseases are:

  1. Hygienic environment
  2. Personal hygiene
  3. Intake of proper nutrition
  4. Intake of clean food and clean water
  5. Regular exercise
  6. Sound sleep

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