(1) Allergy is due to the release of chemicals like histamine and serotonin from the mast cells. Common examples of allergens are mites in dust, pollens, animal dander, etc.
(2)The use of drugs like anti-histamine, adrenaline and steroids quickly reduces the symptoms of allergy.

Cells infected with HIV.
1.Macrophages
2.Helper T-cells(T-lymphocytes).
Events
1.After entry,RNA genome of virus replicates to form viral DNA with help of reverse transcriptase.
2.Viral DNA gets incorporated into host cell's DNA and directs the infected cells to produce viruses.
3.The macrophages produce virus and act like a HIV factory.

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

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.

Health is defined as a state of complete physical,mental and social well-being.
People should be healthy for the following reasons:
(i) Health increases longivity.
(ii) Health reduces infant mortality and maternal mortality.
(iii) Healthy people are more efficient in work and this increases the productivity and economic prosperity.

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. 

The life cycle of a malarial parasite is shown below:

Major groups of psychotropic drugs,examples and effects

Cancer-Diagnosis:
Cancer can be diagnosed/detected by:
(i) Biopsy and histopathological studies of the tissue.
(ii) Blood and bone marrow tests for increased cell counts as in leukaemia.
(iii) Use of techniques like radiography,Magnetic Resonance Imagine (MRI) and computed tomography (CT) for cancer of internal organs.
(iv) Use of antibodies against cancer specific antigens.
(v) Applying principles of molecular biology to detect genes in individuals with inherited susceptibility to certain types of cancer.

Asexual Phase
It occurs in the human host. The sporozoites enter the human body through the bite of an infected female Anopheles mosquito.
They reach the liver through blood and multiply within the liver cells.
Such liver cells burst and release the parasite into blood.
The parasite enters RBCs, multiply in them and cause their rupture.
The rupture of RBCs is associated with the release of a toxin, called haemozoin, which is responsible for the chill/shivering and the high temperature (fever) of the body. Sexual Phase
It starts with the formation of gametocytes in the RBCs of man.
The parasite then enters the female Anopheles mosquito, along with the blood when it bites the infected person.
Further development occurs in the stomach wall of mosquito.
The gametes fuse to form a zygote. The zygote undergoes further development to form sporozoites.
Sporozoites are transported to and stored in the salivary glands of the mosquito and are transferred to a human body during the bite of the mosquito.