All Free Biology MCQs with Answers

2311. Bacteria protect themselves from viruses by fragmenting viral DNA with ____________?

• A. Ligase
• B. Endonuclease
• C. Exonuclease
• D. Gyrase

Explanation: Restriction endonucleases protect bacteria by cutting invading viral DNA at specific internal recognition sequences, thereby disabling the viral genome. Exonuclease is the likely distractor because it also degrades DNA, but it removes nucleotides from an end rather than making the characteristic internal cuts.

2312. Link between living and non-living organisms?

• A. Bacteria
• B. Virus
• C. Cyanobacteria
• D. Plants

Explanation: Viruses are considered a link between living and non-living matter because they show living activity only inside host cells, while outside cells they are inert and can be crystallised. Students may choose bacteria because bacteria are microscopic, but bacteria are complete cellular organisms and are always considered living.

2313. Which of the following CANNOT be transmitted via infectious droplets?

• A. Rubella
• B. Common cold
• C. Influenza
• D. None of the above

Explanation: Rubella, the common cold and influenza can all spread through infectious respiratory droplets, so none of the listed diseases is excluded. Students may choose influenza because they associate it mainly with airborne spread, but respiratory droplets are also an important route of influenza transmission.

2314. Nutritionally Viruses are__________?

• A. Obligate parasite
• B. Autotrophs
• C. Heterotrophs
• D. Absorptive heterotrophs

Explanation: Viruses are obligate parasites because they lack the cellular machinery needed for independent metabolism and reproduction, so they must use a living host cell. Students may choose heterotrophs because viruses obtain materials from hosts, but heterotrophy describes cellular organisms that feed on organic matter, whereas viruses are acellular.

2315. Which of the following viruses has caused thousands of deaths globally as an 'emergent' virus?

• A. MERS
• B. SARS-CoV-2
• C. OC43
• D. HKUt

Explanation: SARS-CoV-2 is an emergent coronavirus that caused the COVID-19 pandemic and millions of deaths worldwide. Students may choose MERS because it is also an emergent coronavirus, but its global death toll and spread were far lower than those of SARS-CoV-2.

2316. Term the time during which an orgnism is present in the body before causing disease ?

• A. Rest period
• B. Incubation period
• C. Sleeping period
• D. Inclubation time

Explanation: The incubation period is the time between entry of a pathogen into the body and the appearance of disease symptoms. A rest period is not a medical term for this interval, while “inclubation” is simply a misspelling; students may choose the latter because it resembles the correct word.

2317. Sporogony of malaria parasite occurs in _______ ?

• A. Liver of man
• B. RBC of man
• C. Stomach wall of mosquito
• D. Salivary glands of mosquito

Explanation: Sporogony is the sexual stage of Plasmodium and occurs in the female Anopheles mosquito, mainly in its stomach wall after fertilisation. Students may choose the liver because Plasmodium multiplies there in humans, but that stage is schizogony, not sporogony.

2318. Tobacco mosaic virus was crystallized by__________?

• A. Pasteur
• B. Chamberland
• C. Stanely
• D. Ivanowski

Explanation: Wendell M. Stanley crystallized tobacco mosaic virus in 1935, demonstrating that viruses could behave like chemical substances outside living cells. Ivanovsky is a likely alternative because he first showed that the agent causing tobacco mosaic disease passed through bacteria-proof filters, but he did not crystallize the virus.

2319. Malarial parasite is injected into man as__________?

• A. sporozoites
• B. merozoites
• C. zygote
• D. none of these

Explanation: The female Anopheles mosquito injects Plasmodium sporozoites into human blood during a bite, and these first travel to liver cells. Merozoites are released later from infected liver or red blood cells, so students may choose them by confusing the next stage with the injected stage.

2320. In human beings influenza is caused by_________?

• A. bacteria
• B. protist
• C. virus
• D. fungi

Explanation: Influenza is caused by influenza viruses, which are enveloped RNA viruses that infect the respiratory tract. Students may choose bacteria because influenza commonly causes fever and respiratory symptoms, but symptoms do not identify the pathogen type.