Read the given passage and answer the following questions:
Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs. As a result of the infection, the alveoli get filled with fluid leading to severe problems in respiration. The symptoms of pneumonia include fever, chills, cough and headache. In severe cases, the lips and finger nails may turn gray to bluish in colour. A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person. Dysentery, plague, diphtheria, etc., are some of the other bacterial diseases in man. Many viruses also cause diseases in human beings. Rhino viruses represent one such group of viruses which cause one of the most infectious human ailments – the common cold. They infect the nose and respiratory passage but not the lungs. The common cold is characterised by nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc., which usually last for 3-7 days. Droplets resulting from cough or sneezes of an infected person are either inhaled directly or transmitted through contaminated objects such as pens, books, cups, doorknobs, computer keyboard or mouse, etc., and cause infection in a healthy person.
Like the common cold in the passage, AIDS is caused by a virus.
Statement I: There is a time-lag between HIV infection and the appearance of AIDS symptoms, which may vary from a few months to many years.
Statement II: After getting into the body of the person, HIV enters into macrophages where the RNA genome of the virus replicates to form viral DNA with the help of the enzyme RNA polymerase.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is correct but Statement II is incorrect.
AIDS (Acquired Immuno Deficiency Syndrome) is caused by HIV (Human Immuno deficiency Virus), a retrovirus with an RNA genome. To make its home in a human cell, the virus must first copy its RNA into DNA.
Statement I: There is a time-lag between HIV infection and the appearance of AIDS symptoms, which may vary from a few months to many years. — True. After infection the virus multiplies quietly, first in macrophages and then in helper T-lymphocytes. Symptoms appear only after the number of helper T-cells has fallen, which can take months to many years.
Statement II: After getting into the body of the person, HIV enters into macrophages where the RNA genome of the virus replicates to form viral DNA with the help of the enzyme RNA polymerase. — False. Making DNA from an RNA template needs reverse transcriptase, an RNA-dependent DNA polymerase. RNA polymerase does the opposite job: it makes RNA from a DNA template during transcription.
NCERT Extract:
AIDS – “… There is always a time-lag between the infection and appearance of AIDS symptoms. This period may vary from a few months to many years (usually 5-10 years). 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. This viral DNA gets incorporated into host cell’s DNA and directs the infected cells to produce virus particles (Figure 7.6).”