Assertion (A): Plant cells possess a large central vacuole. Reason (R): The vacuole stores waste products and maintains turgor pressure. MCQ with Answer and Explanation

Question

Assertion (A): Plant cells possess a large central vacuole. Reason (R): The vacuole stores waste products and maintains turgor pressure.

A. A is true, but R is false.

B. Both A and R are true, but R is not the correct explanation.

C. A is false, but R is true.

D. Both A and R are true, and R is the correct explanation.

Answer: Option D

Solution (By JKExamLibrary)

Mature plant cells contain a large central vacuole that stores water, ions, pigments, and waste products, and is critical for maintaining turgor pressure against the cell wall, providing structural support. The vacuole can occupy up to 90% of cell volume. The reason correctly explains the function of the vacuole, so both statements are true and linked.

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The restriction enzyme EcoRI recognizes the palindromic DNA sequence 5'-GAATTC-3' and cuts the DNA between the:

A. C and G

B. G and A

C. T and C

D. A and T

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Correct Answer: Option B

Explanation:
Restriction enzymes are molecular scissors that cut DNA at specific recognition sites. EcoRI, isolated from Escherichia coli strain RY13, recognizes the 6-base pair palindromic sequence 5'-GAATTC-3'. It cuts the phosphodiester bond between the G and the A on both strands, leaving single-stranded overhangs called 'sticky ends' (5'-AATT-3'). These sticky ends are crucial for joining DNA fragments from different sources using DNA ligase.

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The process by which nitrogen gas is converted to ammonia by bacteria is called:

A. Nitrification

B. Denitrification

C. Nitrogen fixation

D. Ammonification

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Correct Answer: Option C

Explanation:
Biological nitrogen fixation, carried out by symbiotic (Rhizobium) and free-living (Azotobacter) bacteria, reduces atmospheric N₂ to ammonia. Nitrification converts ammonia to nitrates, denitrification returns N₂ to air, ammonification releases ammonia from organic matter.

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The element that is a constituent of the amino acids methionine and cysteine is:

A. Sulfur

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Correct Answer: Option A

Explanation:
Sulfur is present in the amino acids methionine and cysteine (which forms disulfide bonds in proteins). Nitrogen is in all amino acids, phosphorus in nucleic acids and ATP, iron in heme. Sulfur is also in vitamins biotin and thiamine. Disulfide bonds are crucial for protein tertiary structure.

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