It is called allergy.

It is due to the release of histamine and serotonin by mast cells.

(a) Retroviruses
They have RNA as the genetic material and can make DNA on RNA template with the help of enzyme reverse transcriptase;hence they are called retroviruses.
(d) Transmission of HIV infection
(i) by transfusion of blood and blood products contaminated with HIV.
(ii) by sharing infected needles as in the case of intravenous drug abusers.
(iii) from the infected mother to the foetus,through placenta.

(a) Contact inhibition is the property shown by normal cells,by the virtue of which contact with other cells inhibits their uncontrolled proliferation and growth.
(b) All normal cells have cellular oncogenes (c-onc) or proto-oncogenes;when activated under certain conditions,such genes could lead to oncogenic transformation of cells,i.e.they become cancerous.

(i) (vi);
(ii) (v);
(iii) (iv);
(iv) (iii);
(v) (ii);
(vi) (i);
(vii) (viii);
(viii) (vii)

He exhibits withdrawal syndrome.
(i) Withdrawal syndrome refers to the characteristic and unpleasant manifestations of the body of an addict, when regular dose of drugs/alcohol is abruptly discontinued.
Characterstics :
(i) Anxiety
(ii) Excess sweating
(iii) Shakiness
(iv) Nausea
 In some cases, withdrawal symptoms can be severe and even life-threatening.

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.

(a) Amoebiasis is caused by Entamoeba histolytica.
(b) Symptoms:
(i) Constipation 
(ii) Abdominal cramps and pain.
(iii) Stool with excess mucus and blood clots.
Transmission 
Drinking water and food contaminated with the faeces of infected persons.
Houseflies act as mechanical carriers and transmit the parasite from faeces to food and water.

1. Life cycle of Plasmodium in human body.
2. When an infected female Anopheles mosquito bites a person,the sporozoites are injected into the body.
3. They reach the liver cells through blood.
4. The parasite reproduces asexually in the liver cells and by the bursting of liver cells,new cells are released into the blood.
5. They enter the red blood cells (RBCs) and reproduce asexually;by bursting the red blood cells,the cells of the parasite release haemozoin,which causes the cycles of fever,chill and shivering.
6. The released parasite cells infect new red blood cells;some continue the asexual reproduction and cause the cycles of fever.
7. Others enter the sexual stage and form gametocytes in the RBCs,which are picked by the Anopheles mosquito, along with the blood meal.

(i) Histamines cause reactions of the immune system against allergens.
(ii) Interferons protect the non-infected cells of our body from viral infections.
(iii) B-cells produce antibodies against antigens/pathogens.

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 process by which retrovirus gains entry into human host body or the mechanism by which AIDS virus causes immunodeficiency is as follows:

Types and functions.

(i) Normal cells have genes called cellular oncogenes (c-onc) or proto-oncogenes, which are present in inactive state. Also 'contact inhibition' is the property exhibited by normal cells.
It prevents their uncontrolled proliferation when they are in contact with other neighbouring cells.
Thus,when due to certain conditions like mutation oncogenes are turned on, this makes the cells to lose the property of contact inhibition and they continue to divide despite being in contact with other cell, which Jeads to masses of cells called tumours and lead to cancer.
(ii) Cancer can be detected by the following methods
(a) Biopsy In this method a suspected tissue is studied by cutling it into thin sections and staining it for cell examination.
(b) Histopathology lt is the study of diseased cells and tissues taken from the body during biopsy by using amicroscope.
(c) MRI (Magnelic Resonance Imaging) It uses strong magnelic fields and non-ionising radiations to accurately detect pathological and physiological changes in the living tissue.
(iii) Treatment of Cancer
Most cancers are treated by the combination of procedures, surgery, radiotherapy and chemotherapy and immunotherapy. These are explained below
(i) Surgery Tumours are removed by surgery to check further sprcad of cancer cells.
(ii) Radiotherapy Tumour cells are irradiated by lethal doses of radiation while protecting the surrounding normal cells.

(c): Severe combined immunodeficiency (SCID) represents a group of rare, sometimes fatal, congenital disorders characterized by little or no immune response. The defining feature of SCID, commonly known as "bubble boy" disease, is a defect in the specialized white blood cells (B-and T-Iymphocytes) that defend us from infection by viruses, bacteria and fungi. SCID is caused by a defect in the gene that codes for the enzyme adenosine deaminase on chromosome number 20. Lack of the enzyme adenosine deaminase (ADA), means that the substrates for this enzyme accumulate in the cells. Immature lymphoid cells of the immune system are particularly sensitive to the toxic effects of these unused substrates, so fail to reach maturity. As a result, the immune system of the afflicted individual is severely compromised or completely lacking. Lack of this enzyme makes the body defenseless against infections. SCID is the first genetic disorder to be combated with gene therapy.

(b): Allergy is non-infectiousunusual reaction or hypersensitivity of an individual to a foreign substance or agent that may be harmless to other individuals (thus it is considered as immunity disorder). It is non-communicable as it is confined to a person only and does not spread from one person to another. The foreign substance or allergen on first contact functions as mild antigen. It produces antibodies which remain attached with the mast cell. Lysis of mast -cells occur which releases histamine as allergy mediator

(i)

(ii) Primary response appears mainly in the lymph nodes and spleen. Whereas the secondary response appears mainly in the bone marrow, followed by spleen and lymph nodes.
(iii) Trajectory of the above graph is explained as follows In prinary immune response the lag phase is often longer. Level of antibody reaches peak in 7 to 10 days. The first antibody produced is mainly IgM. Although small amount of IgG are also produced. In secondary immune response, lag phase is shorter (1-4 days) due to the presence of memory cell. Level of antibody reaches peak in 3-5 days. Mainly IgG is produced. Usually 1000 times more antibodies are produced here.
(iv) IgG level is higher in secondary response as it can divide faster and produce high-affinity antibodies such as IgG, in response to antigen.

(i) IgE antibody is released in allergic reactions.
(ii) Watery eyes, running nose, wheezing, sneezing, etc.
(iii) Adrenaline and steroids help to suppress and serotonin from the mast cells upon the entry of allergens in body. Thus, the allergic symptoms are either suppressed or reduced.
(iv) Autoimmune diseases are those in which the body begins to attack self-cells, e.g. rheumatoid arthritis, Addison's disease, etc.
(v) There are no permanent cures for autoimmune histamine diseases, but standard treatments available to reduce the signs and symptoms to a certain level.