Immuno - deficiencies are the diseases which occur due to impaired immune responses. These immuno - deficiencies may be primary or secondary. AIDS is a secondary immunodeficiency caused by a retrovirus Human Immunodeficiency Virus (HIV). Following diagram is that of HIV. Observe the diagram and answer the questions listed below the diagram :

(i) State one difference primary immunodeficiency and secondary immunodeficiency.
(ii) Why is HIV called a retrovirus?
(iii) Identify the parts of the diagram labelled as A and B.

Explanation

(i) Primary immunodeficiency is the congenital immunodeficiency of the children e.g. SCID caused by a recessive gene mutation leading to deficiency of enzyme adenosine deaminase , while secondary immunodeficiency is an acquired immunodeficiency which develops after birth e.g. AIDS caused by HIV.
(ii) HIV (Human Immunodeficiency Virus) is called retrovirus as it has single stranded RNA genome which has the power of reverse transcription.
(iii) A = RNA (Genetic material)
B = Reverse transcriptase enzyme