Aids to Health — ICSE Class 9 Biology Important Questions

Answer: (c) Alexander Fleming.

Alexander Fleming discovered penicillin in 1928 from the mould $Penicillium\ notatum$Penicillium notatum. Edward Jenner developed the smallpox vaccine, while Pasteur and Koch pioneered the germ theory of disease.

Answer: (b) Antiseptic.

Antiseptics such as Dettol and tincture of iodine are mild enough to be applied on living tissue. Disinfectants are stronger and used only on non-living surfaces.

Answer: (c) Natural passive immunity.

The baby receives ready-made antibodies from the mother's milk without making them itself, and this transfer occurs naturally, so it is natural passive immunity.

Answer: (b) Immediate but short-lived protection.

Antivenom is an antiserum containing ready-made antibodies (artificial passive immunity). It acts immediately, which is vital in an emergency, but the protection is short-lived because the body has not made its own antibodies or memory cells.

Answer: (a) The common cold is a viral infection; antibiotics such as penicillin act only on bacteria and have no effect on viruses, so they cannot cure a cold. R correctly explains A.

(i) Immunity: The ability of the body to resist and fight against disease-causing organisms and their harmful products.

(ii) Vaccine: A preparation containing weakened, killed or attenuated germs or their products, introduced into the body to stimulate it to produce antibodies and develop immunity against a particular disease.

Antiseptic: Dettol (or tincture of iodine) — applied to living tissue such as skin and wounds to check germs.

Disinfectant: Phenol (or bleaching powder) — used on non-living things such as floors, toilets and drains to kill germs.

Antibiotic: Penicillin (or streptomycin) — taken into the body to kill or check disease-causing bacteria.

Active immunity

• The body produces its own antibodies in response to an antigen or vaccine.
• Develops slowly but lasts long (often lifelong).
• Memory cells are formed.
• Example: immunity after recovering from measles, or after vaccination.

Passive immunity

• Ready-made antibodies are received from an outside source.
• Acts immediately but lasts only a short time.
• No memory cells are formed.
• Example: antibodies passed from mother to baby through milk, or an antiserum injection.

Thus active immunity is self-produced and durable, whereas passive immunity is borrowed and temporary.

Antiseptic

• A mild chemical that checks the growth of germs.
• Applied on living tissues such as skin, wounds and cuts.
• Examples: Dettol, savlon, tincture of iodine.

Disinfectant

• A strong chemical that kills germs.
• Used on non-living objects such as floors, drains and toilets.
• Examples: phenol, bleaching powder, formalin.

A disinfectant cannot be used on the skin because it is too strong (corrosive) and would damage or destroy the living cells of the tissue. Antiseptics are specially made mild so that they harm the germs but not the living tissue.

The tetanus vaccine contains a modified (toxoid) form of the toxin that is harmless but still acts as an antigen.

When introduced into the body, the immune system recognises this antigen and produces antibodies against it. At the same time, memory cells are formed and stored.

If the person is later exposed to the real tetanus germ or its toxin, the memory cells quickly recognise it and produce antibodies rapidly and in large amounts, destroying the pathogen before disease develops. This is active artificial immunity.

Booster dose: Over time the level of antibodies falls and the memory response may weaken. A booster dose re-exposes the body to the antigen, raising antibody levels again and strengthening memory, so protection continues to be effective.

Immunity is the ability of the body to resist disease. It is broadly of two types:

1. Innate (natural/inborn) immunity: Present from birth and non-specific. It includes barriers such as the skin, mucus, tears (containing lysozyme), stomach acid and white blood cells that engulf germs.

2. Acquired (adaptive) immunity: Developed during a person's life and specific to a particular pathogen. It is further divided into:

• Active immunity — the body makes its own antibodies. It is natural (after suffering from a disease) or artificial (after vaccination).
• Passive immunity — ready-made antibodies are received. It is natural (mother to baby through placenta/milk) or artificial (injection of antiserum).

Innate immunity is the first line of defence, while acquired immunity gives specific, longer protection.

Antibiotics are chemical substances produced by micro-organisms (such as certain fungi and bacteria), or made synthetically, which kill or check the growth of disease-causing bacteria within the body. Examples are penicillin, streptomycin and tetracycline.

Usefulness:

• They cure many serious bacterial diseases such as pneumonia, tuberculosis and typhoid.
• They prevent infection of wounds and after surgery.
• They have greatly reduced deaths from bacterial infections.

Precautions while using antibiotics:

1. Take only on a doctor's advice — never self-medicate, as the wrong antibiotic or dose can be harmful.
2. Complete the full course — stopping early lets some bacteria survive and become resistant.
3. Do not overuse or misuse them — unnecessary use leads to antibiotic resistance and destroys useful bacteria in the body.

(Also, antibiotics do not work against viral diseases like colds and flu, so they should not be taken for such infections.)

(i) Such a preparation is called a vaccine, and the process is called vaccination (immunisation).

(ii) The boy developed active (artificial) immunity, because his own body produced antibodies in response to the introduced cowpox material rather than receiving ready-made antibodies.

(iii) The cowpox material acted as an antigen closely resembling the smallpox germ. The boy's immune system recognised it and produced antibodies and memory cells. When he was later exposed to the smallpox germ, the memory cells rapidly produced large amounts of antibodies that destroyed the germ before it could cause disease.

(iv) Any one of: polio, measles, tuberculosis (BCG), tetanus, hepatitis-B — all prevented by vaccination.