The HIV virus weakens the immunity of a person because it destroys
- A.mast cells
- B.platelets
- C.erythrocytes
- D.lymphocytes
Correct answer
Explanation
The correct answer is D, lymphocytes. HIV infects and destroys helper T lymphocytes, the white blood cells that coordinate the body's immune response, so immunity steadily collapses.
HIV, the human immunodeficiency virus, is a retrovirus: it carries RNA and uses the enzyme reverse transcriptase to make DNA copies of its genome inside host cells. Its main target is the helper T cell, also called the CD4 cell. As the virus multiplies, the CD4 count falls, and the body can no longer fight ordinary infections such as tuberculosis and pneumonia. This late stage is AIDS, acquired immunodeficiency syndrome. ELISA is the usual screening test, and antiretroviral therapy keeps the virus in check but does not cure the infection.
A is wrong: mast cells release histamine during allergic reactions and are not HIV's main target.
B is wrong: platelets help blood clot.
C is wrong: erythrocytes, or red blood cells, carry oxygen.
Exam tip: HIV = retrovirus attacking helper T (CD4) cells; screening by ELISA, confirmation by Western blot; World AIDS Day is 1 December.
Practice Questions
View allSyngamy results in formation of
- A.haploid zygote
- B.diploid zygote
- C.non-motile male gametes
- D.motile male gametes
Show answer
Syngamy is the fusion of a male and a female gamete, and since each gamete is haploid, their union gives a diploid zygote.
Read the full explanation →Human insulin molecule is composed of one α-chain having 21 amino acids and one β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?
- A.One
- B.Two
- C.Three
- D.Four
Show answer
Humans have a single functional insulin gene, INS, on the short arm of chromosome 11, and both chains of insulin come from it.
Read the full explanation →Which one of the following is the value of one nanometer?
- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
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One nanometre is 10⁻⁹ metre, and since one metre is 100 (10²) centimetres, it equals 10⁻⁷ centimetre. The prefix nano means one billionth.
Read the full explanation →Which of the following is the general formula for saturated hydrocarbons?
- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
Show answer
Saturated open-chain hydrocarbons are the alkanes, and every alkane fits the formula CₙH₂ₙ₊₂. In a saturated hydrocarbon every carbon atom is joined to others only by single bonds, so each carbon holds the largest possible number of hydrogen atoms.
Read the full explanation →Which one of the following is not an epidemic disease?
- A.Cholera
- B.Malaria
- C.Smallpox
- D.Elephantiasis
Show answer
Elephantiasis, or lymphatic filariasis, is an endemic disease: it stays steadily present in certain regions and develops slowly over years, rather than breaking out suddenly in a large number of people.
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