All Free Biology MCQs with Answers

1371. Ozone depletion occurs commonly due to_______________?

• A. Carbon dioxide
• B. Chlorofluorocarbons
• C. UV rays
• D. Deforestation

Explanation: Chlorofluorocarbons release chlorine radicals in the stratosphere, and these radicals catalytically destroy ozone molecules. UV radiation is absorbed by ozone rather than being the usual cause of its depletion, so c reflects a cause-and-effect confusion.

1372. Destruction of all life forms is called___________?

• A. Sterilization
• B. Disinfection
• C. Antisepsis
• D. Preservation

Explanation: Sterilization destroys or removes all forms of microbial life, including resistant spores, from an object or material. Students may choose disinfection, but disinfection reduces harmful microbes on non-living surfaces and does not necessarily eliminate every organism.

1373. Bacteria which grow either in the presence or absence of oxygen___________?

• A. Aerobic bacteria
• B. Anaerobic bacteria
• C. Facultative bacteria
• D. Microaerophilic

Explanation: Facultative bacteria can grow when oxygen is present and can also switch to anaerobic metabolism when oxygen is absent. Students may choose aerobic bacteria because the question mentions growth with oxygen, but strict aerobes cannot grow without it.

1374. ___________ is used to relieve one kind of headache, migraine?

• A. Pencillin
• B. Lovastatin
• C. Cyclosporine
• D. Ergotin

Explanation: Ergotin, an ergot alkaloid preparation, has been used to constrict cranial blood vessels and relieve migraine attacks. Students may choose penicillin because it is a well-known medicine, but it is an antibiotic and has no specific role in treating migraine.

1375. Control of organisms by using living organisms is called_______?

• A. Bioremediation
• B. Integrated disease management
• C. Antisepsis
• D. Biological control

Explanation: Biological control means managing or reducing a harmful organism by using another living organism, such as using natural predators against crop pests. Bioremediation uses organisms to remove pollutants, so students may select it if they mistake pest control for pollution cleanup.

1376. PCR stand for _________?

• A. Polymerase chain reaction
• B. Poly carbomyl reaction
• C. Peptide chain reaction
• D. Pentapeptide chain reaction

Explanation: PCR stands for Polymerase Chain Reaction, a laboratory method that repeatedly copies a selected DNA segment using primers, nucleotides and a heat-stable DNA polymerase. Students may select peptide chain reaction because “chain reaction” sounds chemically plausible, but PCR specifically concerns polymerase-driven DNA amplification.

1377. The tumours which are of small size and localized are___________?

• A. benign
• B. malignant
• C. gentle
• D. nasty

Explanation: Benign tumours are usually localized, remain relatively small and do not invade nearby tissues in the manner of malignant tumours. Students may choose malignant because it is the medically familiar term for cancer, but malignancy is associated with uncontrolled invasion and possible metastasis.

1378. Blood is carried towards the heart by __________?

• A. Arteries
• B. Capillaries
• C. Veins
• D. none of these

Explanation: Veins return blood towards the heart, using valves and surrounding muscle contractions to prevent backflow, although pulmonary veins are an exception to the usual oxygen-content pattern. Students may choose arteries because they carry blood away from the heart, which is the opposite direction asked here.

1379. Path of Blood present in vessels called __________?

• A. Capillaries
• B. Lumen
• C. Platelates
• D. Plasma

Explanation: The lumen is the hollow internal space of a blood vessel through which blood flows. Capillaries are vessels, whereas plasma is the liquid part of blood and platelets are cellular fragments, so those terms do not name the passage itself. Students often choose capillaries because they are the smallest vessels, but the question asks for the internal channel.

1380. Variation in the size of red blood cells is called __________?

• A. hypochromia
• B. Anisocytosis
• C. Poikilocytosis
• D. Polychromatophilia

Explanation: Anisocytosis means variation in the size of red blood cells, whereas poikilocytosis means variation in their shape. Students often select poikilocytosis by confusing size variation with shape variation.