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 _____.

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Quizplus · Accepted Answer

If the two tracers appeared in a single sieve-tube member, it would suggest that pressure is not the sole driving force behind phloem transport. The pressure-flow hypothesis proposes that pressure gradients move solutes from source to sink, but if both tracers are present in the same sieve-tube member, it suggests that there may be other forces at work, such as active transport or gradients of solute concentration. The appearance of the two tracers in different sieve-tube members, either adjacent or in different vascular bundles, would support the pressure-flow hypothesis.

Researchers Have Investigated Bidirectional Transport in Phloem by Applying Different