Eutrophication in a water body leads to: MCQ with Answer and Explanation

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Eutrophication in a water body leads to:

A. Increased oxygen levels

B. Increased biodiversity

C. Algal blooms and hypoxia

D. Decreased nutrient levels

Answer: Option C

Solution (By JKExamLibrary)

Eutrophication is the excessive enrichment of water bodies with nutrients (primarily nitrates and phosphates from fertilizers and sewage). This leads to rapid growth of algae, known as an algal bloom. When the algae die, their decomposition by bacteria consumes large amounts of dissolved oxygen, leading to hypoxia (low oxygen levels) or anoxia, causing the death of fish and other aquatic organisms.

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Question #1

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Consider statements about plant reproduction: 1. Pollination is the transfer of pollen to the stigma. 2. Double fertilization is unique to gymnosperms. 3. Seeds develop from ovules. Which are correct?

A. 1 and 2 only

B. 1, 2 and 3

C. 1 and 3 only

D. 2 and 3 only

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Correct Answer: Option C

Explanation:
Pollination is the mechanism of transferring pollen grains from the anther to the stigma of a flower. After fertilization, the ovule develops into a seed and the ovary into a fruit. Double fertilization, involving syngamy and triple fusion, is a unique characteristic of angiosperms, not gymnosperms. Therefore, statements 1 and 3 are correct.

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Question #2

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The element that is a key component of the thyroid hormones T₃ and T₄ is:

A. Phosphorus

B. Iodine

C. Iron

D. Calcium

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Correct Answer: Option B

Explanation:
Iodine atoms are incorporated into thyroxine (T₄, 4 iodine atoms) and triiodothyronine (T₃, 3 iodine atoms) synthesized by thyroid follicular cells. Iodine deficiency leads to goiter and hypothyroidism. Iron is in hemoglobin, calcium in bones, phosphorus in ATP and bones.

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Question #3

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In the recombinant plasmid pBR322, the 'rop' gene codes for a protein that:

A. Confers resistance to ampicillin

B. Produces proteins that restrict the growth of the host cell

C. Helps in the replication of the plasmid

D. Confers resistance to tetracycline

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Correct Answer: Option C

Explanation:
pBR322 is a widely used cloning vector. The 'rop' gene (Repressor Of Primer) codes for a small polypeptide that regulates and helps in the replication of the plasmid by inhibiting the synthesis of the RNA primer required for plasmid DNA replication. The 'ampR' and 'tetR' genes confer resistance to ampicillin and tetracycline, respectively, serving as selectable markers. Exam tip: 'rop' = replication control; 'R' = resistance.

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