The World Health Organization [WHO] defines health as a state of complete physical, mental and social wellbeing and not merely absence of diseases.

Personal hygiene, regular exercise, and a balanced diet are very important to maintain good health.

Atropa belladonna and Datura

(i) Male Ascaris is shorter than female Ascaris
(ii)The posterior end of the male worm is carried whereas in female worm this is not found.

(i) An organism which completes its life cycle in two hosts is said to be digenic,
(ii) Eg : plasmodium vivax which casues malaria is a digenic parasite invading man as secondary host and female Anopheles mosquito as primary host.

Mosquito vector	Disease
(a) Aedes aegypti	Dengue fever
(b) Female Anopheles mosquito	Malaria

Rubella Virus - causes Measles
Polio virus - causes Poliomyelitis

Non-infection diseases are not transmitted from an infected person to a healthy person. In origin they may be genetic (cystic fibrosis), nutritional (vitamin deficiency diseases) and degenerative (arthritis, heart attack, stroke).

Autoimmunity is due to an abnormal immune response in which the immune system fails to properly distinguish between self and non-self and attacks its own body. Our body produces antibodies (autoantibodies) and cytotoxic T cells that destroy our own tissues. If disease-state results, it is referred to as auto-immune disease.
Thus, autoimmunity is a misdirected immune response. Eg., Rheumatoid arthritis and multiple sclerosis

Interferons: These are the proteins made and released by host cells in response to the presence of pathogens such as viruses, bacteria, parasites etc
RoIe: They inhibit viral infections and stimulate the entire immune system to fight disease. They also regulate many kinds of cell functions

Life cycle of Plasmodium :
(i) The life cycle of Plasmodium involves three phases namely schizogony,gamogony and sporogony.
(ii) The parasite enters the human blood stream through the bite of an infected female Anopheles mosquito.
(iii) As it feeds, the mosquito injects the saliva containing the sporozoties.
(iv) The sporozoite within the blood stream enter the hepatic cells of the liver.
(v) It undergoes multiple asexual fission (schizogony) and produces merozoties which are released from liver cells.
(vi) The merozoites penetrate the RBC's. Inside the RBC of blood, the merozoite begins to develop unicellular trophozoites. The trophozoite grows in size and a central vacuole develops p them to one side of cytoplasm and becomes the signet ring stage.
(vii) The trophozoite nucleus divides asexually to produce the schizont.

(viii) The schizont divides and produces mononucleated merozoites.
(ix) Eventually the erythrocyte lyses, releasing the merozoites and haemozoin toxin into the blood stream to infect other erythrocytes.
(x) Lysis of red blood cells results in fever and other symptoms.
(xi) This erythrocytic stage is cyclic and repeats itself approximately every 48 to 72 hours or longer depending on the species of Plasmodium involved.
(xii) The sudden release of merozoites triggers an attack on the RBCs.
(xiii) Occasionally, merozoites differentiate into macrogametocytes and microgametocytes. when these are ingested by a mosquito, they develop into male and female gametes respectively.

1. Effectively dealing with peer pressure:
The biggest reason for teens to start on drugs is due to their friends/peer groups imposing pressure on them. Hence, it is important to have a better group of friends to avoid such harmful drugs and alcohol.
2. Seeking help from parents and peers:
Help from parents and peer group should be sought immediately so that they can be guided appropriately. Help may even be sought from close and trusted friends. Getting proper advice to sort out their problems would help the young to vent their feelings of anxiety and guilt.
3. Education and counselling:
Education and counselling create a positive attitude to deal with many problems and to accept disappointments in life.
4. Looking for danger signs:
Teachers and parents need to look for a sign that indicates a tendency to go in for addiction.
5. Seeking professional and medical assistance:
Assistance is available in the form of highly qualified psychologists, psychiatrists and deaddiction and rehabilitation programmes to help individuals to overcome their problems.

Different types of antigen and antibody reactions: The reaction between soluble antigen and antibody leads to the visible precipitate formation, which is called a precipitin reaction. Antibodies that bring about precipitate formation on reacting with antigens are called as precipitins. Whenever a particulate antigen interacts with its antibody, it would result in clumping or agglutination of the particulate antigen, which is called agglutination reaction. The antibody 'involved in bringing about agglutination reaction is called agglutinin. Opsonisation or enhanced attachment is the process by which a pathogen is marked of ingestion and destruction by a phagocyte. Opsonization involves the binding of an opsonin i.e., antibody, to a receptor on the pathogens. cell membrane. After opsonin binds to the membrane, phagocytes are attracted to the pathogen. So, opsonization is a process in which pathogens are coated with a substance called an opsonin, marking the pathogen out for destruction by the immune system. This results in a much more efficient phagocytosis. The neutralization reactions are the reactions of antigen-antibody that involve the elimination of the harmful effects of bacterial exotoxins or a virus by specific antibodies. These neutralizing substances i.e. antibodies are known. as antitoxins. This specific antibody is produced by a host cell in response to a bacterial exotoxin or corresponding toxoid (inactivated toxin).

Lymph node has three zones. They are the cortex, paracortex, and medulla. The outer most layer of the lymph node is called cortex, which consists of B-lymphocytes, macrophages, and follicular dendritic cells. The paracortex zone is beneath the cortex, which is richly populated by T lymphocytes and interdigitating dendritic cells. The innermost zone is called the medulla which is sparsely populated by lymphocytes, but many of them are plasma cells, which actively secrete antibody molecules. As the lymph enters, it slowly percolates through the cortex, paracortex, and medulla, giving sufficient chance for the phagocytic cells and dendritic cells to trap the antigen brought by the lymph. The lymph leaving a node carries enriched antibodies secreted by the medullary plasma cells against the antigens that enter the lymph node. Sometimes visible swelling of lymph nodes occurs due to active immune response and increased the concentration of lymphocytes. Thus swollen lymph nodes may signal an infection. There are several groups of lymph nodes. The most frequently enlarged lymph nodes are found in the neck, under the chin, in the armpits, and in the groin.

Thymus is most active during the neonatal and pre-adolescent periods. The. thymus is a fiat and bilobed organ located behind the stemun, above the heart. Each lobe of the thymus contains numerous lobules, separated from each other by connective tissue called septa. Each lobule is differentiated into an outer cortex and an inner medulla. Within each lobule, the developing T cells called thymocytes are arranged into outer cortex and inner medulla. The inner medulla contains immature thymocytes and outer cortex has matured thymocytes. One of its main secretions is the hormone thymosin. It stimulates the T cell to become mature and immunocompetent. By the early teens, the thymus begins to atrophy and is replaced by adipose tissue.

S. No	Active Immunity	Passive Immunity
1.	Active immunity is produced actively by host's immune system	Passive immunity is received passively and there is no active host participation
2.	It is produced due to contact with pathogen or by its antigen.	It is produced due to antibodies obtained from outside
3.	It is durable and effective in protection.	It is transient and less effective
4.	Immunological memory is present	No memory
5.	Booster effect on subsequent dose is possible.	Subsequent dose is less effective
6.	Immunity is effective only after a short period	Immunity develops immediately

Helminths are mostly endoparasitic in the gut and blood of human beings and cause diseases called helminthiasis. The two most prevalent helminthic diseases are Ascariasis and Filariasis. Ascaris is a monogenic parasite and exhibits sexual dimorphism. Ascariasis is a disease caused by the intestinal endoparasite Ascaris lumbricoides commonly called the roundworms. It is transmitted through ingestion of embryonated eggs through contaminated food and water. Children playing in contaminated soils are also prone to have a chance of transfer of eggs from hand to mouth. The symptoms of the disease are abdominal pain, vomiting, headache, anemia, irritability, and diarrhoea. A heavy infection can cause nutritional deficiency and severe abdominal pain and causes stunted growth in children. It may also cause enteritis, hepatitis, and bronchitis.
Filariasis is caused by Wuchereria bancrofti, commonly called filarial worm. It is found in the lymph vessels and lymph nodes of man. Wuchereria bancrofti is sexually dimorphic, viviparous and digenic. The life cycle is completed in two hosts, man and the female Culex mosquitoes. The female filarial worm gives rise to juveniles called microfilariae larvae. In the lymph glands, the juveniles develop into adults. The accumulation of the worms blocks the lymphatic system resulting in inflammation of the lymph nodes. In some cases, the obstruction of lymph vessels causes elephantiasis or filariasis of the limbs, scrotum and mammary glands

(i) A vaccine is a biological preparation that provides active acquired immunity to a particular disease and resembles a disease-causing microorganism and is often made from weakened or attenuated or killed forms of the microbes, their toxins, or one of its surface proteins.
(ii) Vaccines "teach" our body how to defend itself when viruses or bacteria, invade it.
(iii) Vaccine initiates the immunization process. The vaccines are classified as first, second and third generation vaccines.
First generation vaccine:
(i) First generation vaccine is further subdivided into live attenuated vaccine, killed vaccine and toxoids.
(ii) Live attenuated live vaccines use the weakened (attenuated), aged, less virulent form of the virus
(iii) Eg. Measles, Mumps and Rubella (MMR) vaccine and the Varicella (chickenpox) vaccine, killed (inactivated) vaccines are killed or inactivated by heat and other methods. Eg. Salk's polio vaccine.
(iv) Toxoid vaccines contain a toxin or chemical secreted by the bacteria or virus.
(v) They make us immune to the harmful effects of the infection, instead of to the infection itself.
(vi) Eg. DPT vaccine (Diphtheria, pertussis and Tetanus), (Triple antigen).
Second generation vaccine: contains the pure surface antigen of the Pathogen. :
Eg. Hepatitis-B vaccine 
Third generation vaccine: contains the purest and the highest potency vaccines which are synthetic in generation. The latest revolution in vaccine is DNA vaccine (or) recombinant vaccine

(i) After getting into the body of the person, the virus enters into macrophages where RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase.
(ii) This viral DNA gets incorporated into the DNA of host cells and directs the infected cells to produce viral particles.
(iii) The macrophages continue to produce viral particles and act like a HIV factory. simultaneously, HIV enters into helper T-lymphocytes (T_H), replicates and produces progenies viruses.
The progenies viruses are released into the blood attack other helper T-lymphocytes. This is repeated, leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person.
(v) During this period, the person suffers from bouts of fever, diarrhea and weight loss. Due to decrease in the number of helper T-lymphocytes, the person starts suffering from infections that could have been otherwise overcome, such as those due to bacteria especially mycobacterium viruses; fungi and even parasites like toxoplasma.
(vi) The patient becomes so immune deficient that he/she is unable to protect himself/herself against infections.

Sporozoites.
After entering the bloodstream of host it finally reaches the liver cell.

The secondary immune response occurs when a person is exposed to the same antigen again. During this time, immunological memory has been established and the immune system can start producing antibodies immediately. Within hours after recognition of the antigen, a new army of plasma cells are generated. Within 2 to 3 days, the antibody concentration in the blood rises steeply to reach much higher level than primary response. This is' also called as "booster response".

Innate immunity is the natural phenomenon of resistance to infection which an individual possesses right from the birth. The innate defense mechanisms are non-specific in the sense that they are effective against a wide range of potentially infectious agents. It is otherwise known as non-specific immunity or natural immunity

Kala-azar or visceral leishmaniasis is caused by Leishmania donovani, which is transmitted by the vector Phlebotomus (sand fly). Infection may occur in the endothelial cells, bone marrow, liver, lymph glands and blood vessels of the spleen. Symptoms of Kala-azar are weight loss, anaemia, fever, enlargement of spleen and liver

Several people complain of stomach discomfort or pain and trouble with bowel movements, causing diarrhoea. This is called irritable bowel syndrome and caused by stress or other illnesses

According to the World Health Organization (WHO), hygiene refers to "conditions and practices that help to maintain health and prevent the spread of diseases."

Inside the human RBC, the merozoite of plasmodium begins to develop as unicellular trophozoites. The trophozoite grows in size and a central vacuole develops pushing them to one side of cytoplasm and becomes the signet ring stage.

In the 1950s, experiments conducted by Porter and Edelman revealed the basic structure of the immunoglobulin.
An antibody molecule is Y shaped structure that comprises of four polypeptide chains, two identical light chains (L) of molecular weight 25,000 Da (approximately 214 amino acids) and two identical heavy chains (H) of molecular weight 50,000 Da (approximately 450 amino acids). The polypeptide chains are linked together by di-sulphide (S-S) bonds. One light chain is attached to each heavy chain and two heavy chains are attached to each other to form a Y shaped structure. Hence, an antibody is represented by H₂L₂.
The heavy chains have a flexible hinge region at their approximate middles.
Each chain (L and H) has two terminals. They are C - terminal (Carboxyl) (or) -COOH and amino or N-terminal (or NH₂). Each chain (L and H) has two regions and they have variable (V) region at one end and a much larger constant (C) region at the other end.
Antibodies responding to different antigens have very different (V) regions but their (C) regions are the same in all antibodies.
In each arm of the monomer antibody, the (V) : regions of the heavy and light chains combine to form an antigen - binding site shaped to 'fit' a specific antigenic determinant.
Consequently each antibody monomer has two such antigen - binding regions.
The (C) regions that forms the stem of the antibody class and serve common functions in all antibodies.
The functions of immunoglobulin are agglutination, precipitation, opsonisation neutralization etc.