Which one among the following hormones inhibits the growth activity in plants?
- A.Auxins
- B.Cytokinins
- C.Abscisic acid
- D.Gibberellins
Correct answer
Explanation
The correct answer is C, Abscisic acid. It is the main growth inhibitor among plant hormones and works against the growth promoters. Abscisic acid, or ABA, is called the stress hormone because it helps plants survive drought, cold and salt: it makes the stomata close to save water, keeps seeds and buds dormant so they do not sprout in bad weather, and helps leaves and fruits to age and fall. So when a question asks which hormone slows or stops growth, ABA is the answer; ethylene is the other hormone linked with ageing and ripening. A is wrong, because auxins promote growth by making cells elongate, and they make shoots bend towards light. B is wrong, because cytokinins promote cell division and delay the ageing of leaves. D is wrong, because gibberellins promote stem elongation, break seed dormancy and are sprayed on grapes to increase their size. Exam tip: the growth promoters are auxin, gibberellin and cytokinin; the inhibitor is abscisic acid, the stress hormone.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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