All Free Biology MCQs with Answers

1901. The air spaces may comprise upto _________ of total volume of leaf surface?

• A. 30%
• B. 20%
• C. 40%
• D. 50%

Explanation: Intercellular air spaces can occupy about 40% of a leaf's total volume, providing pathways for carbon dioxide and oxygen movement between the stomata and photosynthetic cells. Students may choose 30% because they underestimate the extensive air spaces present between mesophyll cells.

1902. There are _________ stomata per square cm of leaf surface in Tobacco plants?

• A. 1200
• B. 12000
• C. 100,000
• D. 1000

Explanation: Tobacco leaves may have about 100,000 stomata per square centimetre of leaf surface, allowing substantial exchange of carbon dioxide, oxygen and water vapour. Students may choose 12,000 per square centimetre because that value is a plausible stomatal density for some other plants, but it is too low for the stated textbook value for tobacco.

1903. Water is _________ times viscous than air?

• A. 50
• B. 1000
• C. 5000
• D. 8000

Explanation: At ordinary temperature, water is approximately 50 times more viscous than air, so gases diffuse much more readily through air than through water. Students may choose 1000 because water feels much thicker than air, but viscosity is a measured physical ratio rather than a comparison based on sensation.

1904. Of the following, which one is better respiratory medium___________?

• A. Air
• B. Water
• C. Soil
• D. None of these

Explanation: Air is a better respiratory medium than water because it contains a much higher concentration of oxygen and gases diffuse more rapidly through it. Students may choose water because aquatic animals also respire successfully, but water is a poorer medium and must be passed over respiratory surfaces continuously.

1905. Gaseous exchange in birds occurs at level of_______________?

• A. Alveoli
• B. Air sacs
• C. Bronchi
• D. Parabronchi

Explanation: Birds exchange gases across the thin walls of parabronchi, where air flows continuously through tubes surrounded by capillaries. Air sacs act mainly as bellows for ventilation and are not the principal exchange surface, so b is the common mistake.

1906. Morgan studied how many traits of Drosophila?

• A. 7
• B. 67
• C. 85
• D. All

Explanation: Morgan studied about 85 inherited traits and mutations in Drosophila, using them to investigate genes, chromosomes and linkage. Students may choose 67 because it is another large number, but it is not the commonly cited number of traits in this historical account.

1907. First time crossing over was observed in ___________?

• A. 1811
• B. 1927
• C. 1911
• D. 1990Educational Resources

Explanation: Crossing over was first observed and reported in 1911, during early genetic studies of linked genes and chromosome exchange. Students may choose 1927 because that date is associated with other important genetics research, but it was not the first observation of crossing over.

1908. How many types of genomic mapping are there?

• A. 2
• B. 4
• C. 5
• D. None of these

Explanation: Genomic mapping is commonly divided into two main types: genetic mapping, based on recombination frequency, and physical mapping, based on actual DNA distances. Students may choose 4 because several individual mapping techniques exist, but the broad categories are two.

1909. The appendix is situated in the ____________?

• A. Left Lower Quadrant
• B. Right Upper Quadrant
• C. Right lower Quadrant
• D. Left Upper Quadrant

Explanation: The appendix is a narrow, finger-like projection from the caecum, which lies in the right lower quadrant of the abdomen. Students may choose the left lower quadrant by confusing the appendix with the descending or sigmoid colon. Therefore, option c matches its normal anatomical location.

1910. Enzyme present in the saliva is_____________?

• A. lipase
• B. trypsin
• C. ptyalin
• D. invertase

Explanation: Ptyalin is the salivary enzyme, also called salivary amylase, and it begins the digestion of starch into smaller carbohydrates in the mouth. Trypsin acts in the small intestine, while lipase mainly digests fats, so students often choose trypsin because it is another well-known digestive enzyme. Invertase is not the standard enzyme identified with saliva.