Stimuli, Receptors and Responses - Part 3

A tropic response is

• a growth response.

• produced by certain part of a plant.

• a response to a unilateral stimulus.

• a slow response.

Phototropic response

• is a response to uniform light.

• is positive in root tip.

• is negative in shoot tip.

• allows the maximum absorption of light by leaves.

By comparing the results of experiments 1, 2 and 3, what conclusion can you made?

• Shoot is positively phototropic.

• The shoot tip is the receptor of unilateral light.

• The region just below the shoot tip is the receptor of unilateral light.

• None of them listed.

Gelatin block inserted in between the shoot tip and the shoot is permeable to chemical but not to electrical signal. What deduction(s) can be made from the experimental result?

• A chemical is diffusing from shoot tip to the region below to cause the bending of the shoot.

• An electrical signal is diffusing from shoot tip to the region below to cause the bending of the shoot.

Mica barrier allows electrical signal to pass through but not a chemical signal. A mica barrier is inserted to left side of the shoot and another mica barrier is inserted to right side of another shoot. Both shoots are exposed to unilateral light. The results are shown in the diagram. What deduction(s) can be made from the experiments?

• The signal that causes bending of the shoot is an electrical one.

• The signal that causes bending of the shoot is a chemical one.

• Unilateral light may cause an uneven distribution of auxins on the left and right sides of the shoot.

• Unilateral light has no effect on the distribution of chemical on the left and right sides of the shoot.

The shoot tip was cut and placed back on the left side of the shoot. The shoot was then bend towards the right in complete darkness. What deduction(s) could you made?

• Left side of the shoot (with the shoot tip) has a higher concentration of a chemical which causes faster elongation growth just below.

• Left side of the shoot grew faster than the right side which causes the bending of the shoot towards the right

• The signal which causes bending of the shoot is an electrical one.

If the concentration of auxins is 10^-4 ppm, this will

• stimulate the growth of root.

• stimulate the growth of shoot.

• have no effect on the growth of shoot.

• inhibit the growth of shoot.

If the auxins concentration is 6 ppm, this

• stimulates the growth of root.

• has no effect on the growth of root.

• inhibits the growth of root.

• stimulates the growth of shoot.

If uniform light is provided to the shoot,

• auxins diffuse evenly from the shoot tip to the region of elongation below on both left and right side of the shoot.

• the same concentration of auxins causes the same elongtation growth as observed on both left and right side of the shoot.

• left and right side of the shoot grow evenly and there is an upright elongation of the shoot.

If light is illuminated from one side,

• this causes lateral diffusion of auxins from lighted/illuminated side to the shaded/unilluminated side of the shoot.

• a higher concentration of auxins at the shaded side of the shoot stimulates faster elongation growth.

• a lower concentration of auxins at the lighted side of the shoot stimulates slower elongation growth.

• lighted and shaded sides of the shoot elongate differently and causes the bending of the shoot towards the light.