Diseases and First Aid Chapter Notes | Biology Class 8 ICSE PDF Download

Introduction

This chapter teaches us about health, diseases, and how to help someone in an emergency. We learn what makes a person healthy, the different types of diseases, how they spread, and how to prevent them. It also explains first aid steps for common problems like burns, bleeding, and snake bites. Understanding these topics helps us stay healthy and safe.

Health

• Normally, a person is healthy if they are not suffering from any disease.
• A healthy person can work hard, get along well with others, enjoy free time, and handle stress to live a good life.
• Health means being completely well in body, mind, and social life, not just being free from disease or weakness.
• Physical health and mental health are connected; a healthy mind needs a healthy body, and a healthy body needs a healthy mind.
• A healthy person usually has these features:
  • Clear skin.
  • Bright and clear eyes.
  • Not too fat or too thin body.
  • Fresh breath.
  • Good appetite (eating well).
  • Deep and sound sleep.
  • Regular activity of bladder and bowels (good toilet habits).
  • Coordinated body movements (moving easily and well).
• Disease means a change from normal health due to a problem in the body’s structure or function.

Categories of diseases

There are two main types of diseases:

• Non-communicable or non-infectious diseases: These do not spread from one person to another and are not caused by germs.
• Communicable or infectious diseases: These spread from a sick person to a healthy person through germs or pathogens.

Types of non-communicable or non-infectious diseases

Below is a simplified classification of non-infectious diseases along with common examples:

• Metabolic – e.g., diabetes mellitus, goitre
• Genetic – e.g., haemophilia, thalassemia
• Allergies – e.g., hay fever, asthma
• Dietary deficiency – e.g., beri-beri, scurvy, goitre
• Cancer – e.g., breast cancer, leukemia
• Degenerative (due to ageing) – e.g., arthritis, cataract
• Caused by physical or chemical factors – e.g., injury, heat, cold, radiation, poisoning
• Mental disorders – e.g., depression

Metabolic Diseases (also called Organic Diseases)

• These are caused by improper functioning of body organs. One example is diabetes, where the pancreas fails to release enough insulin, the hormone that regulates blood sugar. As a result, excess sugar is eliminated through urine.
• Heart diseases, such as a heart attack (coronary thrombosis), occur when the blood supply to heart muscles is blocked, preventing the heart from working properly.
• You may also recall learning about kidney malfunction, where the nephrons—which filter harmful nitrogenous wastes—fail. This leads to the accumulation of toxic substances in the blood, causing a condition known as uraemia.

Genetic Diseases or Congenital Diseases

• These arise during embryonic development due to defective genes or chromosomes passed down from parents.
• In haemophilia, blood clotting happens very slowly because certain necessary clotting factors are missing.
• Thalassemia involves abnormal hemoglobin in red blood cells. Affected children often need regular blood transfusions to survive.

Allergy

• An allergy is an abnormal and unpredictable reaction to a specific substance, known as an allergen. Individuals may react differently to various allergens. 
• Common triggers include dust, fungal spores, pollen, specific fabrics, medicines, and cosmetics. Allergic reactions commonly impact the skin, respiratory system, and digestive tract. Conditions such as asthma, eczema, diarrhoea, vomiting, and nausea are frequent symptoms resulting from allergic responses.

Dietary Deficiency Diseases

• When the diet lacks essential nutrients like proteins, which are vital for body growth and tissue repair, it can lead to muscle wasting and weight loss. Diseases caused by protein deficiency include kwashiorkor and marasmus.
• A lack of vitamins in the diet can result in various deficiency diseases such as night blindness, pellagra, scurvy, and beri-beri.

Neoplastic Diseases or Uncontrolled Cell Growth

These diseases involve abnormal and excessive growth of body cells, such as in cancers or tumors. Factors that may lead to cancer include smoking, chewing tobacco, drug abuse, pollution, radiation, and even certain viruses. Substances that trigger cancer are known as carcinogens.

Degenerative Diseases

As people age, the structure and function of body cells and organs gradually weaken. Age-related conditions include:

• Cataract – the eye lens becomes cloudy, leading to vision loss
• Arthritis – swelling and pain in the joints
• Arteriosclerosis – stiffening of artery walls, which restricts blood flow

​Diseases Caused by Physical and Chemical Agents

Some diseases arise due to environmental or chemical exposure. Examples of physical causes include sunburn and heat stroke. Harmful chemical agents include substances like lead, mercury, potassium cyanide, as well as snake venom and toxic plants, all of which can lead to serious health conditions or poisoning.

Communicable or infectious diseases

• Communicable diseases spread from a sick person to a healthy person through microorganisms like viruses, bacteria, fungi, or protozoa.
• These germs, also called pathogens, spread through air, water, food, physical contact, cuts, sexual contact, or insects like mosquitoes and flies.

1. Diseases caused by viruses

• Cold: The most common disease that spreads through tiny droplets when a sick person sneezes or coughs.
• Influenza (flu): A common disease with symptoms like cold, fever, and chills. Spreads through droplets when a sick person coughs or sneezes.
• Mumps: Caused by swelling of the parotid glands (salivary glands below the ears). Spreads through contact, handkerchiefs, crockery, or utensils used by the sick person.
• Smallpox: A serious disease with small pustules (bumps) all over the body. Spreads by contact and discharge from these pustules. It has almost been removed from India.
• Poliomyelitis (polio): Causes paralysis of the limbs (arms or legs). Spreads by contact through discharge from the nose, throat, or fecal matter.
• Measles: Spreads by contact, causing nasal discharge, red eyes, and coughing.
• Rabies/hydrophobia: Caused by the bite of a rabid dog, fox, or other animals. The virus spreads through the saliva of the animal. A serious disease that affects the central nervous system. Pet dogs must be vaccinated to prevent this.
• Jaundice/hepatitis: Affects the liver, causing yellow skin and eyes. Spreads by eating unhygienic food or drinking contaminated water.
• AIDS (Acquired Immune Deficiency Syndrome): Caused by the HIV (Human Immunodeficiency Virus). Weakens the body’s immune system (ability to fight diseases). Spreads to many people through unsafe practices like sharing needles or unsafe sexual contact. Infectious diseases spread through sexual contact, blood transfusion, and infected needles. Children can get them from the mother during pregnancy or breastfeeding.

2. Diseases caused by bacteria

• Tuberculosis (TB): It is caused by bacteria. It mostly affects the lungs but can also affect other body parts. An infected person spreads it through the sputum (cough droplets).
• Diphtheria: It is usually a disease of children and affects the throat. The jaws get locked, and germs enter through open and unclean cuts and wounds.
• Whooping Cough (Pertussis): It occurs in children and spreads through the cough droplets of an infected person. The patient coughs with a peculiar sound.
• Pneumonia: It is a disease of the lungs caused by bacteria. It spreads through the sputum of an infected person. It causes vomiting and breathing problems.
• Cholera: It is due to the infection in the intestines caused by bacteria. It spreads through contaminated food and water.

3. Diseases Caused by Moulds and Fungi

• Fungi enter the body through the skin in the form of spores (tiny particles).
• Ringworm causes a disease with ring-shaped patches on the skin, hair, or nails, marked by ring-shaped patches.
• Athlete’s foot attacks the skin of the foot, between the toes.

4. Diseases Caused by Protozoa

• Malaria is caused by a protozoan called Plasmodium, spread by the bite of a female Anopheles mosquito.
• It causes symptoms like chills and high fever.
• It is caused by Entamoeba and attacks large intestines.
• Symptoms include loose motions with gripping pain in the stomach, discharge of mucus, and blood in stools in severe cases.
• In acute conditions, blood accumulates in the faeces.
• It is caused by consuming contaminated food.

5. Diseases Caused by Worms

• Elephantiasis is caused by worms, leading to swollen legs and scrotum in males and breasts in females.
• It spreads by the bite of female Culex mosquito.
• Ascariasis is caused by parasites in the intestines, absorbing digested food, leading to stomach pain.
• Eggs of parasites may be found in unwashed fruits and vegetables in the soil.
• Taeniasis is caused by the tapeworm in the intestine, found in improperly cooked pork or beef.

Spread of Communicable Diseases

Try to race out the body of an infected person and reach out to healthy hosts for survival. These pathogens transfer from a patient to a healthy person in different ways.

Direct Method

Certain diseases, such as measles, chickenpox, and fungal infections, can spread through direct physical contact with an infected individual.

Indirect Method

Disease transmission can also occur indirectly through several ways:

• Sharing personal items: Using the same towel, handkerchief, bed, or utensils as an infected person can transfer germs to a healthy individual, leading to illness.
• Consuming contaminated food or water: Many digestive system-related diseases are spread by eating unwashed vegetables or fruits, or consuming items rinsed in polluted water. Once the germs enter the digestive tract, they multiply and cause disease.
• Vectors and carriers: These are organisms, like mosquitoes and houseflies, that carry disease-causing germs without being infected themselves. For instance, a mosquito feeding on a person with malaria picks up the parasite and can later transmit it to a healthy person through its bite.
• Air: Many viral and bacterial diseases like tuberculosis spread through the air. For example, germs of tuberculosis pass into the air during sneezing or coughing of the patient. These germs remain suspended in the air for some time, and a healthy person gets the infection by inhaling them. Tuberculosis, chickenpox, and diphtheria spread in this way.

Preventive Measures for Diseases

We must observe the following preventive measures for good health.

1. Prevention of Deficiency Diseases

• Eat healthy and proper diet with seasonal fruits and vegetables to develop body resistance against diseases.
• Cereals should be cooked well.
• Cut vegetables immediately, otherwise, vitamins may get destroyed.
• Wash vegetables before peeling and eat whole fruits as far as possible.
• Avoid too much frying of vegetables.

2. Public Hygiene

• It involves proper disposal of human excreta and domestic wastes.
• Sewage and chemical wastes should not be thrown into nearby water bodies.
• Water bodies should be cleaned to avoid water-borne diseases.

3. Healthy Environment

• Maintain a healthy environment to prevent the spreading of diseases due to breeding of mosquitoes and house flies.
• Do not allow water to remain stagnant outside your house and in your neighborhood.
• All the drains should also be covered.

4. Immunization

• Immunization and vaccination on time can prevent infectious diseases.

5. Personal Hygiene

Hygiene refers to the science and practice of maintaining good health, and personal hygiene means taking proper care of one’s own body.

• Skin Care: Bathing regularly with a good soap helps keep the skin clean, removes dirt, and prevents body odour.
• Hands and Nails: It's important to wash hands thoroughly before meals. Nails should be trimmed short, and nail-biting should be avoided, as it can transfer dirt and harmful microbes into the mouth.
• Hair: Hair should be washed frequently using shampoo to eliminate dirt, dandruff, and lice. Personal grooming items like combs and brushes should not be shared.
• Teeth and Gums: Brushing after every meal and gently massaging the gums helps prevent tooth decay and gum bleeding. Good oral hygiene is essential for a healthy mouth.
• Eyes: Rinse eyes daily with clean water. Read in proper lighting and limit time spent on screens like TVs, computers, and video games. Avoid direct exposure to sunlight. Eye infections such as trachoma and conjunctivitis can spread through contaminated items like towels and handkerchiefs.
• Nose: Clean the nose regularly to remove trapped dirt and mucus. Cover your nose and mouth while sneezing or coughing to prevent the spread of germs through airborne droplets.
• Ears: Avoid using sharp objects to clean the ears, as this may damage the eardrum and lead to hearing problems. Ears naturally clean themselves through wax, which traps dust and germs.
• Physical Exercise: Regular exercise keeps muscles strong and supports the healthy functioning of the heart, lungs, and blood circulation.
• Rest: Adequate sleep and rest are important for good health. Most healthy individuals need 6–8 hours of sleep each night.
• Healthy Habits: Good habits include eating meals on time, going to bed early (but not immediately after eating), and avoiding harmful substances like alcohol, tobacco, and drugs, which can disrupt sleep and harm the body. Excessive consumption of fast food (like burgers and pizza) should be avoided, as these are low in vitamins and can lead to obesity.

First Aid

As the name implies, first aid refers to the immediate help provided to someone during an emergency before medical professionals arrive. This is essential in situations like accidents, heart attacks, snake bites, burns, and more.

• Burns: The treatment depends on how severe the burn is.
• Do not remove clothing stuck to the burn or pop blisters. You may apply ointments, butter, or vaseline.
• For minor burns, run cold water over the area, pat it dry, and cover it with a sterile dressing.
• For serious burns, do not use water. Just cover the wound with clean dressing.
• For chemical burns (from acid or other substances), rinse the area under running water for 10 minutes, then apply a clean dressing.
• Bleeding: Elevate the injured limb to reduce blood flow. Clean the wound with water, apply gentle pressure using clean cotton, and if available, use a mild antiseptic.
• Fractures: Keep the injured person still and comfortable. Loosen or remove clothing near the injured area. Avoid moving the fractured part. If it's the arm, support it with a sling.
• Eye Injuries: If a foreign object gets into the eye, do not rub it. Gently wash the eye with clean water.
• Unconsciousness: Lay the person flat and comfortably, loosen tight clothing, and ensure the room is well-ventilated to allow fresh air.
• Heart Attack: Lay the person down horizontally and ensure there's plenty of fresh air around.
• Swallowing Poison: If someone consumes a poisonous substance, have them drink saltwater to trigger vomiting.
• Snake Bite: Try to squeeze out some blood from the wound and apply a tight band (tourniquet) above the bite to slow the spread of venom.
• Stings (Bee/Wasp): If the sting remains, remove it, then gently squeeze out some blood to release venom. Apply an alkaline substance like baking soda to the area.

Fever

When you feel body ache, cold and your body temperature is more than 98.6°F, it indicates that you are suffering from a fever. A fever is not a disease but it is a symptom of some disease.

Fever with High Temperature

• In case of a high fever, you can immediately apply an ice pack or a piece of cloth dipped in ice-cold water on the forehead of the patient to bring down the body temperature.
• If the fever persists for more time, consult the doctor immediately.

Vaccination

The concept of vaccination was introduced by Edward Jenner (1749–1823). He noticed that milkmaids exposed to cowpox did not contract smallpox. To test this observation, he took material from a cowpox sore and injected it into an eight-year-old boy. The boy developed mild pustules which healed on their own, leaving a scar.

• Two months later, Jenner injected the boy with smallpox, but the boy did not develop the disease, confirming Jenner's theory. Jenner called the substance used a "vaccine" (from the Latin word vacca, meaning cow), and the process was named vaccination. 
• His discovery was later validated by Louis Pasteur, who created vaccines for diseases like anthrax, chickenpox, and cholera.
• Vaccination refers to the artificial introduction of germs or germ substances into the body to help it develop immunity against certain diseases. This preventive method is scientifically known as prophylaxis, and the substance introduced is called a vaccine. Vaccines are commonly injected (e.g., TAB vaccine) or given orally (e.g., polio drops). 
• Once inside the body, the vaccine stimulates white blood cells (WBCs) to produce antibodies that fight the targeted germs.
  

Though the terms "vaccine" and "vaccination" were originally used in relation to smallpox, they now apply to many diseases. Vaccines can be created in four main ways:

• Killed Germs: These vaccines contain dead germs and are used in vaccines such as TAB (typhoid), Salk’s vaccine (polio), and the rabies vaccine.
• Weakened Live Germs: In this method, germs are weakened so they can't cause disease but can still trigger antibody production. Examples include vaccines for measles and the freeze-dried BCG vaccine for tuberculosis.
• Fully Active Germs: In the case of smallpox, vaccination involved the use of the cowpox virus, which is similar to the smallpox virus. However, smallpox vaccines are no longer administered as the disease has been nearly eradicated in India.
• Toxoids: These are made from harmless forms of bacterial toxins, treated with formalin to neutralize their harmful effects while retaining their ability to stimulate antitoxin production. Toxoid vaccines are used for diseases like diphtheria and tetanus.

Immunization

• Immunization is an artificial way of achieving protection from infections.
• Scientists have been able to manufacture vaccines for various diseases (attenuated) pathogens that the pathogens release, which have been rendered harmless (toxoids), the body makes antibodies to such vaccines, the body makes antibodies.
• Latin means cow and the process was confirmed by Louis Pasteur, and he produced vaccine for anthrax, chickenpox, cholera, etc.
• ics for developing resistance to particular disease.
• The idea of vaccination was conceived by Edward Jenner (1749-1823), he observed that milkmaids who were in contact with cows suffering from cowpox never got small pox.
• He tested his theory on an eight-year-old boy, he injected small pox into the boy’s body, and he developed pustules which later on formed a scab and healed leaving only a scar.
• To further test his idea, he injected the boy with small pox after two months, and he found no sign of small pox on the boy, in this way, Jenner’s vaccination experiment was successful, he used the term ‘vaccine’ for immunity inducing preparation (Vaccin in Latin means cow).
• The polio programme is going on till date, so far, you all must be quite familiar with it, it is followed to eradicate polio curse from our country.

Bad Habits to be Avoided

• Harmful effects of consuming tobacco or tobacco products increases the risk of lung cancer, heart attacks, irritation in eyes, cough, and many others in active smokers may suffer from such diseases, this is known as passive smoking.
• Alcohol affects the mental and physical processes of the body, alcohol may affect the central nervous system, stomach, liver, kidneys, and blood vessels, the consumption of the body resulting in self-control, it also affects muscular coordination.
• Harmful effects of drugs, which cause insensible condition in human beings are called narcotic drugs, e.g., cocaine, heroin, morphine, marijuana, opium, such drugs cause serious damage to the nervous system and cause respiratory and heart problems, addiction to these drugs may cause a variety of health problems and early death.