[Campbell Biology P.896] Based on the experiments described in Figure 39.5, which of the fol... | Practice Question

Based on the experiments described in Figure 39.5, which of the following conclusions is best supported?

  • A: The entire coleoptile perceives light and directly initiates the bending response.
  • B: Light perception occurs at the coleoptile tip, and the signal for bending is a mobile chemical substance.
  • C: The phototropic signal is transmitted through an impermeable physical connection from the tip to the bending region.
  • D: Removing the coleoptile tip or covering it with any cap prevents phototropic bending due to a lack of light exposure.

Explanation

The combined findings of Darwin and Boysen-Jensen, as summarized in the conclusion, strongly support that the coleoptile tip is where light is perceived, and a mobile chemical signal is then transmitted from the tip to cause bending. Options A and D contradict Darwin's findings regarding the specific role of the tip and the effect of transparent caps. Option C contradicts Boysen-Jensen's finding that the signal passes through a permeable barrier.