Which one of the following is essential for thyroid gland to make thyroxin?
- A.NaCl
- B.KCl
- C.Cholesterol
- D.Iodine
Correct answer
Explanation
The correct answer is D, Iodine. Thyroxine is an iodine-containing hormone, so the thyroid gland cannot make it without iodine from the diet.
The thyroid is a butterfly-shaped gland in the neck. It takes up iodine from the blood and joins it to the amino acid tyrosine to make thyroxine (T4), which has four iodine atoms, and triiodothyronine (T3). These hormones control the body's rate of metabolism, growth and the development of the brain in children. When the diet lacks iodine, the gland swells as it tries to make more hormone, causing goitre; severe lack in pregnancy can cause cretinism in the child. This is why India adds iodine to common salt.
A is wrong because sodium chloride is only the carrier in iodised salt; it is not part of the hormone. B is wrong because potassium chloride plays no part in making thyroxine. C is wrong because cholesterol is the raw material for steroid hormones such as cortisol and sex hormones, not for thyroxine.
Exam tip: iodine deficiency causes goitre; thyroxine is T4, with four iodine atoms.
Practice Questions
View allIn plant cells, RNA is present in
- A.cytoplasm only
- B.nuclei and cytoplasm only
- C.nuclei, cytoplasm, mitochondria, chloroplast and endoplasmic reticulum
- D.nuclei, cytoplasm, mitochondria, chloroplast and ribosomes
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In plant cells RNA is found in the nucleus, the cytoplasm, mitochondria, chloroplasts and ribosomes. RNA is made in the nucleus, where DNA is copied into messenger, transfer and ribosomal RNA; the nucleolus in particular is rich in ribosomal RNA.
Read the full explanation →Cell wall is absent in which one of the following organisms ?
- A.Bacteria
- B.Diatom
- C.Mushroom
- D.Tapeworm
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The tapeworm is an animal, and animal cells have no cell wall, only a cell membrane. A rigid cell wall lies outside the cell membrane in plants, fungi, most bacteria and many protists, giving the cell shape and protection.
Read the full explanation →Methanol is toxic because
- A.methanol coagulates the protoplasm
- B.methanol gets oxidised to methanal in liver which coagulates the protoplasm
- C.methanol gets oxidised to acetic acid in liver which coagulates the protoplasm
- D.methanol gets oxidised to CO in liver which coagulates the protoplasm
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In the liver, methanol is oxidised to methanal (formaldehyde), which coagulates protoplasm and damages cells. Methanol, CH3OH, is the simplest alcohol and is sometimes mixed into illicit liquor.
Read the full explanation →In which one of the following types of connective tissues in animals does fat get stored?
- A.Adipocyte
- B.Chondrocyte
- C.Osteocyte
- D.Reticulocyte
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Adipocytes are the fat cells of adipose tissue, a loose connective tissue that stores fat in animals. Adipose tissue lies mainly beneath the skin and around organs such as the kidneys and heart.
Read the full explanation →Which one of the following agents does not contribute to propagation of plants through seed dispersal?
- A.Wind
- B.Fungus
- C.Animal
- D.Water
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Seeds are carried away from the parent plant by wind, water and animals, but fungi play no part in seed dispersal.
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