The plant growth regulators are small, simple molecules of diverse chemical composition. They are
- A.carbohydrates, fats and proteins
- B.indole compounds, adenine derivatives, carotenoids and terpenes
- C.fatty acids, glucose and vitamins
- D.vitamin C, vitamin D and glucose
Correct answer
Explanation
The correct answer is B, indole compounds, adenine derivatives, carotenoids and terpenes. Plant growth regulators, or plant hormones, are small molecules that control growth even in tiny amounts, and each main group comes from a different chemical family. Auxins such as indole-3-acetic acid (IAA) are indole compounds; they cause cell elongation, apical dominance and rooting. Cytokinins such as kinetin are adenine derivatives; they promote cell division and delay ageing of leaves. Abscisic acid (ABA) is derived from carotenoids; it is the stress hormone that closes stomata and keeps seeds dormant. Gibberellins such as gibberellic acid (GA3) are terpenes; they lengthen stems and help seeds germinate. The fifth group is a gas, ethylene, which ripens fruit. Option A is wrong because carbohydrates, fats and proteins are the bulk food molecules of living things, not regulators. Option C is wrong because fatty acids, glucose and vitamins are nutrients and building blocks. Option D is wrong because vitamin C, vitamin D and glucose are not plant hormones. Exam tip: auxin is an indole, cytokinin an adenine derivative, ABA from carotenoids, gibberellin a terpene, and ethylene a gas.
Practice Questions
View allEqual volumes of all gases, under the same conditions of temperature and pressure, contain an equal number of molecules. This statement is known as
- A.Avogadro's law
- B.Boyle's law
- C.Charles's law
- D.Dalton's law of partial pressures
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It is the reason one mole of every gas occupies the same 22.4 litres at standard temperature and pressure, and it allowed chemists to settle the formulae of gases such as hydrogen and oxygen as having two atoms each.
Read the full explanation →Carbon forms two oxides, carbon monoxide and carbon dioxide, in which twelve grams of carbon combines with sixteen grams and thirty two grams of oxygen respectively. This illustrates
- A.The law of conservation of mass
- B.The law of constant proportions
- C.The law of multiple proportions
- D.Avogadro's law
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When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other bear a simple whole number ratio, and here the oxygen masses of sixteen and thirty two grams for the same twelve grams of carbon are in the ratio…
Read the full explanation →How many moles are present in 36 grams of water?
- A.One mole
- B.Two moles
- C.Three moles
- D.Half a mole
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The molecular mass of water is eighteen unified atomic mass units, two hydrogen atoms of 1 u each and one oxygen atom of 16 u, so one mole of water weighs eighteen grams.
Read the full explanation →One unified atomic mass unit, written as u, is defined as
- A.The mass of one hydrogen atom
- B.One twelfth of the mass of one atom of carbon twelve
- C.One sixteenth of the mass of one atom of oxygen
- D.The mass of one electron
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This standard was adopted so that the atomic masses of all elements could be compared on one relative scale, and on it hydrogen comes out as about 1 u, oxygen as 16 u and chlorine as 35.5 u. Option A is wrong because the hydrogen atom was the standard in…
Read the full explanation →At standard temperature and pressure, the volume occupied by one mole of any gas is
- A.11.2 litres
- B.22.4 litres
- C.24.4 litres
- D.1 litre
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It follows from Avogadro's law: since equal volumes of all gases at the same temperature and pressure contain an equal number of molecules, one mole of hydrogen, of oxygen or of carbon dioxide all take up the same space at standard temperature and pressure, even though their masses are two…
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