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Question
The following diagram shows four coleoptiles set up at the start of an experiment.
Which two coleoptiles will both bend towards the light source?
The following diagram shows four coleoptiles set up at the start of an experiment.
Which two coleoptiles will both bend towards the light source?
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Solution
The correct option is D III and IV
Auxin concentration increases in shaded area, i.e., auxins are collected on the opposite side of light. Increased concentration of auxin is stimulatory for shoot growth and for this reason, shaded side shows more growth than the lighted side. Hence, bending of the shoot takes place towards light.
In the coleoptile experiment, if light is shown on a coleoptile, it starts bending from one side towards light. The bending occurs due to elongation of the part just below the coleoptile, some influence is transmitted from tip to basal region which results in curvature. So, here in thegiven sets of experiment only in III and IV, the coleoptiles will bend towards the unlilateral light source, as in III the razor blade is used in the right side and the unlilateral source is also in the same direction, which causes secretion of auxin in the shaded direction, which causes bending. While in experiment IV, no razor blade is used, so there will be secretion of auxin in the shaded direction and this causes bending of coleoptile.
In experiment I, the direction of light is direct, because the other part is removed by the razor blade and hence no auxin synthesis will take place, and so there will be no bending. While in II experiment the apical portion of coleoptile is removed, and so there will be no bending.
Thus, the correct answer is 'III and IV.'
Auxin concentration increases in shaded area, i.e., auxins are collected on the opposite side of light. Increased concentration of auxin is stimulatory for shoot growth and for this reason, shaded side shows more growth than the lighted side. Hence, bending of the shoot takes place towards light.
In the coleoptile experiment, if light is shown on a coleoptile, it starts bending from one side towards light. The bending occurs due to elongation of the part just below the coleoptile, some influence is transmitted from tip to basal region which results in curvature. So, here in thegiven sets of experiment only in III and IV, the coleoptiles will bend towards the unlilateral light source, as in III the razor blade is used in the right side and the unlilateral source is also in the same direction, which causes secretion of auxin in the shaded direction, which causes bending. While in experiment IV, no razor blade is used, so there will be secretion of auxin in the shaded direction and this causes bending of coleoptile.
In experiment I, the direction of light is direct, because the other part is removed by the razor blade and hence no auxin synthesis will take place, and so there will be no bending. While in II experiment the apical portion of coleoptile is removed, and so there will be no bending.
Thus, the correct answer is 'III and IV.'
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