Many secondary metabolites obtained from plants are used for their medicinal properties, e.g. opiates derived from poppy plant are used as drugs to relieve pain. 
The problem starts when these metabolites are misused for having pleasure and are taken in doses above the prescribed limit, e.g. opium addict loses weight, fertility and interest in work.

Passive smoking can be equally dangerous because it exposes the person to the same harmful effects of smoke. Passive smoking means being in the same room or place, where some one is smoking and getting exposed to smoke in the surrounding area.
Once inhaled, the smoke can trigger mucus release in the bronchioles that blocks the airways. This induces coughing. But prolonged exposure can lead to bronchitis, emphysema, respiratory tract infections and eventually lung cancer.

The symptoms of ascariasis include internal bleeding, muscular pain, fever, anaemia and blockage of intestinal passage. A healthy person may acquire this infection by consuming food and water, etc., contaminated with faeces of infected person.

Mother's milk is considered most appropriate or a boon for a newborn infant as it provides immunity in the initial period of baby's life. The yellowish fluid colostrum secreted by mother during the intial days of lactation has abundant antibodies (IgA) to protect the infant.

When the body encounters a pathogen for the first time, it triggers an immune response by generating antibodies.

This response is of low intensity. Subsequent encounter with same pathogen elicits a highly intensified secondary response.

This is ascribed to the fact that our body appears to have memory of the first encounter. this types of secondary immune response is elicited by memory T-cells, B-cell which keep ready to mount a rapid and vigorous attack as soon as the same pathagen infects the body again.

H₂,L₂ represent two small light chains and two large heavy chains in an antibody molecule.

RNA pathogenic viruses are more mutable because RNA is less stable biomolecule than DNA.RNA is single stranded with no complimentary nucleotide pairing.So the nucleotides are readily affected by mutagenic factors.

For successful organ transplantation, the transplant organ should have histocompatibility and blood group compatibility with the recipient,the chances of which are very high if the donor is an identical twin having genetic similarity.

Mostly Stimulant drugs (caffeine) and alcohol give feeling of intoxication and euphoria for only brief period soon after use.However, prolonged use for long-term causes permanent damage to vital body parts like liver, kidneys, lungs,cardiovascular system etc.

1. Proper vaccination
2. Taking in of clean food, pure potable water a inhalation of clean air.
3. Maintain personal an community hygiene.