Consider statements about genetics: 1. DNA is double-stranded. 2. RNA contains thymine. 3. Genes are located on chromosomes. Which are correct? MCQ with Answer and Explanation

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Consider statements about genetics: 1. DNA is double-stranded. 2. RNA contains thymine. 3. Genes are located on chromosomes. Which are correct?

A. 1 and 2 only

B. 1, 2 and 3

C. 1 and 3 only

D. 2 and 3 only

Answer: Option C

Solution (By JKSSB Mock Tests)

DNA is typically a double-stranded helical molecule carrying genetic information. Genes are specific sequences of DNA located linearly on chromosomes. RNA is generally single-stranded and contains the nitrogenous base uracil instead of thymine, which is found in DNA. Therefore, statements 1 and 3 are correct, while statement 2 is incorrect.

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Question #1

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The vitamin that is a component of the coenzymes FMN and FAD is:

A. Niacin

B. Pantothenic acid

C. Riboflavin

D. Thiamine

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Correct Answer: Option C

Explanation:
Riboflavin (vitamin B₂) is the precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are electron carriers in redox reactions. Thiamine is TPP, niacin NAD/NADP, pantothenic acid CoA.

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Question #2

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Which of the following is a fungal disease of plants?

A. Crown gall

B. Tobacco mosaic

C. Citrus canker

D. Late blight of potato

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Correct Answer: Option D

Explanation:
Late blight of potato is caused by the oomycete Phytophthora infestans (historically considered a fungus). It caused the Irish Potato Famine. Tobacco mosaic is viral, citrus canker is bacterial (Xanthomonas), crown gall is bacterial (Agrobacterium tumefaciens). Fungal plant diseases also include rust, smut, and powdery mildew. Oomycetes are now classified under Chromista but traditionally studied in mycology.

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Question #3

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Which of the following pairs is a symbiotic nitrogen fixer in leguminous plants?

A. Anabaena - Azolla

B. Rhizobium - Soybean

C. Azotobacter - Wheat

D. Frankia - Casuarina

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Correct Answer: Option B

Explanation:
Rhizobium species form root nodules in leguminous plants like soybean, pea, and bean, where they fix atmospheric nitrogen symbiotically. Azotobacter is free-living, Anabaena associates with Azolla (a fern), Frankia with non-leguminous plants like Casuarina and Alnus. This symbiosis reduces the need for nitrogen fertilizers in agriculture.

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