Revision Notes: Aids To Health | Biology Class 9 ICSE PDF Download

Aids to Health

Health refers to a state of complete physical, mental, and social well-being, not just the absence of disease or weakness.

Immunity

Immunity is the ability of an organism to fend off harmful substances such as pollutants and pathogens that can enter the body. Our body's defense system operates on two levels:

(A) Local Defence System : This system acts as the first line of defense, preventing the entry of germs into the body.

(B) Immune System : This system comes into play once germs have breached the initial barriers and entered body tissues.

Local Defence System

The Local Defence System consists of various protective mechanisms that work to keep harmful microorganisms at bay.

1. Protective Mechanical Barriers

• Skin: The skin, composed of the protein keratin, acts as a formidable barrier against germs. Any break in the skin, such as a cut or scratch, can allow germs to enter. When the skin is injured, blood clots form to seal the cut, preventing the ingress of harmful microorganisms.
• Hair: Hair located inside the nostrils plays a crucial role in trapping dust and germs, preventing them from entering the respiratory system.

2. Thrown Out if Entered

• Coughing, Sneezing, and Vomiting: These are direct methods the body uses to expel germs or foreign particles that have managed to enter.

3. Germ-Killing Secretions

• Saliva, Sweat, Tears, and Nasal Secretions: These bodily fluids contain substances that help kill germs.
• Hydrochloric Acid: Secreted by the stomach, hydrochloric acid plays a vital role in killing germs that enter the body with food.

4. Germ-Fighting White Blood Cells (WBCs)

• WBCs: White blood cells are a crucial part of the body’s defense system. They engulf and destroy germs through a process known as phagocytosis, helping to protect the body from infections.

Merits of the Local Defence System

• Works instantaneously.
• Effective against a wide range of potentially infectious agents.

Immune System

Immunity can be broadly classified into two main categories: (a) Innate Immunity (b) Acquired Immunity

(a) Innate Immunity: This type of immunity is inherited from parents and is present from birth.

I. Non-specific Innate Immunity: This refers to the general natural resistance to all infections, regardless of the specific pathogen.

II. Specific Innate Immunity: This is the natural resistance to a particular kind of germ or pathogen.

(b) Acquired Immunity: This type of immunity is developed during the lifetime of an organism and involves resistance to specific diseases.

I. Actively Acquired Immunity: This immunity is developed due to a previous infection or exposure to a pathogen.

II. Passively Acquired Immunity: This type of immunity is provided from an outside source in the form of antibodies.

a. Naturally Acquired Passive Immunity: This occurs when a mother’s antibodies reach the fetus through the placenta, providing immunity to the newborn.

b. Artificially Acquired Passive Immunity: This involves antiserum injections to stimulate the production of antibodies, providing temporary immunity.

Differences between Active Immunity and Passive Immunity

Antigen

An antigen is a substance that triggers an immune response in the body. It is typically a protein or a carbohydrate found on the surface of pathogens such as bacteria, viruses, and fungi. When the immune system detects an antigen, it produces antibodies to fight off the invading pathogen. Antigens can also be found on the surface of cancer cells, which is why some cancer treatments involve boosting the immune response against these specific antigens.

Toxin and Antitoxin/Antibodies

• Toxin: A toxin is a poisonous substance produced by living organisms such as animals, plants, or bacteria. Toxins can cause harm or even death to other organisms. For example, snake venom is a toxin produced by snakes that can cause severe harm to their prey. Similarly, some insects produce sting poisons that are toxic to other animals.
• Antitoxin/Antibodies: Antitoxins, also known as antibodies, are proteins produced by the immune system in response to toxins. When a toxin enters the body, the immune system recognizes it as a harmful substance and produces antibodies to neutralize it. For example, antivenins are used to treat snake bites. These antivenins are antibodies produced in response to snake venom and are injected into the patient to counteract the effects of the toxin.

Characteristics of Antibodies

• Antibodies are a type of protein known as immunoglobulins.
• They are produced by a type of white blood cell called lymphocytes.
• Our body has the ability to produce a wide variety of antibodies.
• Antibodies are specific to particular antigens, meaning they can only act on a specific antigen.

AIDS (Acquired Immunodeficiency Syndrome)

• AIDS is caused by the infection of the Human Immunodeficiency Virus (HIV).
• This virus attacks the immune system, specifically targeting T-cells.
• When T-cells are infected and die, they release new viruses that go on to infect more cells.
• HIV is transmitted through:
• Sexual intercourse
• Sharing contaminated needles
• Blood transfusion
• From an infected mother to her unborn fetus
• World AIDS Day is observed on December 1st to raise awareness about the severity of AIDS and the available protective measures.

Vaccination and Immunisation

Vaccination is the process of introducing dead or weakened germs into the body of a living being to develop immunity against a specific disease.

Kinds of Vaccines:

• Killed Germs (e.g., TAB Vaccine)
• Living Weakened Germs (e.g., BCG Vaccine)
• Living, Fully Poisonous Germs (e.g., Cowpox Vaccine)
• Toxoids

Immunisation is the process of developing resistance to disease-causing germs or their toxins by introducing killed germs or germ substances to induce the production of specific antibodies.

Antiseptics and Disinfectants

• Antiseptics: Mild chemical substances that kill germs when applied to the body. Examples include Lysol (dilute), carbolic acid, iodine, benzoic acid, mercurochrome, and boric acid.
• Disinfectants: Strong chemical substances applied to areas where germs thrive and multiply. Examples include cresol, phenol, Lysol, 40% formalin, lime, Bordeaux mixture, and DDT.
• Antibiotics are chemical substances produced by some microorganisms that can kill or inhibit the growth of other microorganisms.
• Penicillin, the first antibiotic discovered by Alexander Fleming, is an example of an antibiotic.

Sources of Antibiotics

Penicillin is commercially produced from the fungus Penicillium chrysogenum.

Streptomycin, a widely used antibiotic, is obtained from the bacterium Streptomyces.

Uses of Antibiotics

Antibiotics are used for various purposes, including:

• Fighting infections: Antibiotics are primarily used to combat bacterial infections in humans and animals.
• Food preservation: Antibiotics can be used to preserve food by preventing the growth of harmful bacteria.
• Animal feed treatment: Antibiotics are sometimes added to animal feed to promote growth and prevent disease in livestock.
• Controlling plant pathogens: Antibiotics can be used to control bacterial infections in plants.

In 1930, a group of chemicals known as sulphonamides was discovered, which proved effective against various bacterial diseases. Examples of sulphonamides include Sulphadiazine and sulphanilamide.