Symptoms of AIDS:
 (i) Swollen lymph nodes.
 (ii) Fever
 (iii) Night sweats.
(iv) Loss of body weight
(v) Infection by pathogen.

Components of Our Immune System:
(i) Lymphoid organs.
(ii) Lymphoid tissues
(iii) Lymphoid cells.
 (iv) Antibodies.

(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.

Two special types of lymphocytes in humans are B-lymphocytes and T-lymphocytes. B-lymphocytes execute antibody-mediated response while T-lymphocytes show cell-mediated response.

B-lymphocytes and T-lymphocytes

Both these types of cella multiply and produce a clone of cells.

B-lymphocytes produce an array of proteins,called antibodies.

The T-lymphocytes stimulate the B-cells to produce antibodies.

Memory B-cells and T-cells remain inthe body,for secondary immune response,in case of subsequent encounter by the pathogen.

HIV  can also be transmitted to a healthy person by
(i) Sharing of infected needles & sergical instruments.
(ii) From infected mother to the foetus 
(iii) Transfusion of infected Blood
(b) Leads to complication in life later; pelvic inflammatory diseaes (p1D)/abortion/infertility/ cancer of reproductive trait still birth, ectopic prequencies STDs are curable if detected early & treated preperly otherwise they may etc

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

Symptoms of Common Cold:
(i) Nasal congesion and discharge.
(ii) Sore throat and hoarseness.
(iii) Cough.
(iv) Headache.
It is caused by rhinoviruses.

Factors to achieve good health:
(i) Awareness about diseases and their effects on different body functions.
(ii) Vaccination/immunisation against many infectious diseases.
(iii) Control of vectors.
(iv) Proper disposal of wastws/excreta.
(v) Periodic cleaning and disinfecting of water reservoirs,tanks,etc. to avoid water-borne diseases.
(vi) Consumption of clean food and drinking water.
(vii) Exercise and relaxation.

1. After entering the body of a person,the virus enters the macrophages.
2. The viral genome (RNA) undergoes replication and reverse transcription  to become viral DNA with the help of reverse transcriptase.
3. The viral DNA gets incorporated into the DNA of the cells and directs these cells to produce virus particles.
4. The macrophages function as HIV factory and produce a number of HIV particles.
5. These HIV particles move out of macrophages and infect the helper T-lymphocytes and replicant to produce progeny viruses.
6. The progeny viruses released in the blood attack new helper T- cells.
7. This process is repeated and there is a progressive decrease in the number of helper T-cells. 

Primary atypical pneumonia is a community-acquired pneumonia caused by Mycoplasma pneumoniae which lacks the cell wall.Due to absence of cell wall,it is resistant to enzymes and penicillin

(i) Ascariasis
Cause. It is caused by Ascaris lumbricoides.(round worm).
Symptoms.Its symptoms include:
(a) Blockage of intestinal passage,
(b)Anaemia,
(c)Abdominal/muscular pain,
(d)Internal bleeding,
(e)Nausea and headache.
Modes of transmission. Infection is through contaminated vegetables, fruits and water as eggs of parasite excreted by the infected persons contaminate soil, plants and water
(ii) Filariasis/Elephantiasis
Cause. It is caused by wuchereria bancrofti and wuchereria malayi(filarial worms)
They normally cause inflammation of the organs in which they live for many years.
They normally affect the lymph vessels of the lower limbs (causing them to swell like that of an elephant, hence called elephantiasis).
Genital organs may also be affected leading to gross deformation.
Modes of transmission. The female culex mosquito is the vector.
(iii)Ringworms
Cause. These are caused by fungi like microsporum, Epidermophyton and Trichophyton
Symptoms. The symptoms include
(i) dry scaly lesions on skins, nails and scalp.
(ii)lesions are accompanied by itching.
Modes of transmission. Ringworms are generally acquired from soil or by direct contact with the contaminated articles used by the infected persons.

It is true that once a person gets entangled in the deadly whirlpool of alcohol or drugs, it is very difficult to get rid of this habit because, in the absence of a continuous supply of alcohol/drugs, the person starts showing certain symptoms called withdrawal signs which are listed below:
(1) Anxiety  
(2) Shakiness
(3) Nausea  
(4)Sweating.

Treatment of cancer:
The following methods (one or in combination) can help to treat cancer.
(i) Surgery
The tumour cells are surgically removed to reduce the load of cancerous cell.
(ii) Radiotheraphy
The tumour cells are irradiated wholly (but taking care of the surrounding normal cells) with safe doses of radiations.
(iii) Chemotherapy
Certain drugs are used to kill the cancerous cells,but majority of the drugs have side effects like hair fall,anaemia,etc.
(iv) Immunotherapy
This involves the use of biological response-modifiers,like alpha-interferon,which activate the immune system and help in destroying the tumour.