Researchers have investigated bidirectional transport in phloem by applying different radioisotope tracers to two source leaves and monitoring a point between the two sources for the presence of the tracers. Which of the following observations would not support the pressure- flow hypothesis? Appearance of the two tracers in

Question

Quizplus · Accepted Answer

The pressure-flow hypothesis suggests that phloem sap moves directionally from source to sink driven by differences in pressure between the two. Appearance of the two tracers in a single sieve-tube member would indicate a lack of directionality and support an alternative hypothesis such as the diffusion hypothesis. Tracers appearing in sieve-tube members of different vascular bundles or adjacent sieve-tube members of the same vascular bundle would still support the pressure-flow hypothesis as they indicate directional transport from source to sink.

Researchers Have Investigated Bidirectional Transport in Phloem by Applying Different