All Free Biology MCQs with Answers

381. A mother infected with HIV can pass the virus to her child

• A. during pregnancy, during delivery and through breastfeeding
• B. only through the genes she passes on
• C. only if the child is vaccinated
• D. never, since HIV requires a needle to spread

Explanation: Mother to child transmission can occur across the placenta, at birth and in breast milk, which is why antiretroviral treatment during pregnancy sharply cuts the risk. HIV is never inherited through genes, since it infects cells rather than the germ line.

382. Which everyday contact does NOT transmit HIV?

• A. Sharing needles contaminated with infected blood
• B. Sexual contact with an infected person
• C. Transfusion of infected blood
• D. Sharing a meal with an infected person

Explanation: HIV needs direct access to blood or mucous membranes, so casual contact such as meals, handshakes and sneezing carries no risk. Knowing this is essential both for prevention and for ending the isolation of infected people.

383. Combination antiretroviral therapy uses several drugs at the same time because

• A. single drugs are too expensive to manufacture
• B. the drugs increase each other's side effects
• C. HIV develops resistance rapidly to any single drug
• D. they kill the virus directly by oxidation

Explanation: HIV mutates so fast that a population resistant to one drug soon appears, but becoming resistant to three at once is far harder. That is why cocktail therapy suppresses the virus for years even though it cannot eliminate the provirus.

384. HIV is classified within which subgroup of retroviruses?

• A. Oncoviruses
• B. Lentiviruses
• C. Spumaviruses
• D. Adenoviruses

Explanation: Lentiviruses, meaning slow viruses, cause long incubation, persistent infections, which fits HIV's years long course from infection to AIDS. Oncoviruses cause cancers and adenoviruses are DNA viruses, so neither group contains HIV.

385. Blood banks test every donated unit of blood for HIV primarily to

• A. prevent transmission of the virus through transfusion
• B. increase the storage life of the blood
• C. raise the red cell count of the unit
• D. detect anaemia in the donor

Explanation: One unit of infected blood can transmit HIV directly into the recipient's circulation, so screening donated blood is one of the most effective barriers to spread. The tests used have nothing to do with storage or cell counts.

386. The envelope glycoprotein gp120 of HIV is important because it

• A. makes vaccination unnecessary
• B. destroys the host's red blood cells
• C. binds to receptors on host cells and allows the virus to enter
• D. makes the virus resistant to heat

Explanation: gp120 projects from the envelope and locks onto CD4 receptors, the first step of infection, which is why it is also the main target researchers aim antibodies at. It has no role against heat or red cells.

387. Which statement about HIV is correct?

• A. It can be cured with a course of antibiotics
• B. It survives for weeks on dry surfaces
• C. It is commonly spread by mosquito bites
• D. It destroys helper T cells and progressively weakens immunity

Explanation: HIV replicates inside helper T lymphocytes and destroys them, so immunity collapses and opportunistic infections follow. Antibiotics cannot touch a virus, the virus dies quickly outside the body, and mosquitoes do not transmit it.

388. The overall equation of aerobic respiration is C6H12O6 + 6O2 giving

• A. 6CO2 + 6H2O + energy
• B. C2H5OH + 6CO2 + energy
• C. 2C3H6O3 + energy only
• D. 6CO2 + energy only

Explanation: Complete oxidation of glucose yields six molecules each of carbon dioxide and water with the release of energy, largely captured as ATP. Alcohol and lactate appear only in the incomplete breakdown of anaerobic respiration.

389. Although glucose stores far more energy, the immediate energy currency used directly for cellular work is

• A. glucose
• B. ATP
• C. glycogen
• D. NADH

Explanation: ATP releases a small, manageable packet of energy when one phosphate is hydrolysed, so it can power single reactions without waste. Glucose must first be respired to recharge ATP, which is why ATP is called the currency and glucose the reserve.

390. One molecule of ATP is composed of

• A. adenine, ribose and three phosphate groups
• B. adenine, deoxyribose and three phosphate groups
• C. guanine, ribose and two phosphate groups
• D. adenine, glucose and three phosphate groups

Explanation: ATP is a nucleotide: the base adenine joined to the sugar ribose and a chain of three phosphates. The sugar is ribose rather than deoxyribose, which is why ATP belongs to the RNA family of nucleotides.