[Campbell Biology P.849] A plant is growing new leaves rapidly while simultaneously developi... | Practice Question

A plant is growing new leaves rapidly while simultaneously developing new fruits. Which of the following is most likely to be true regarding sugar transport in this plant?

  • A: The new leaves will primarily act as sugar sources, exporting sugar to other parts of the plant.
  • B: The developing fruits will compete with growing roots for sugar from nearby sugar sources.
  • C: The direction of sap flow in all sieve tubes connecting different parts of the plant will be unidirectional towards the roots.
  • D: Photosynthesis in mature leaves will decrease due to increased sugar demand from new leaves and fruits.

Explanation

Growing leaves and developing fruits are both significant sugar sinks, meaning they consume large amounts of sugar for growth. The text states that 'a growing fruit may monopolize the sugar sources that surround it' and 'growing roots... are sugar sinks'. Therefore, developing fruits and growing roots would compete for the available sugar supply from sugar sources like mature leaves . The direction of sap flow is not necessarily unidirectional towards the roots, as it depends on the specific source-sink relationship for each sieve tube. Increased demand for sugar would generally stimulate, not decrease, photosynthesis in mature leaves.