Dr. Sharon Hood studies which phenotypic characteristics make pines more likely to survive in the presence of mountain pine beetle infestation. Currently, pine trees in the west are facing an unprecedented attack by mountain pine beetles. Females burrow into the bark of pines and lay their eggs immediately beneath the bark. When the larvae hatch, the chew extensive tunnels through the phloem. The tunnels destroy thick bands of phloem tissue and fully disconnect the top portion of the tree from the bottom resulting in tree death.

Which of the following accurately describes how destroying the phloem would kill the tree?

Taken from “Whitebark pine (Pinus albicaulis) growth and defense in response to mountain pine beetle outbreaks”

Question

Dr. Sharon Hood studies which phenotypic characteristics make pines more likely to survive in the presence of mountain pine beetle infestation. Currently, pine trees in the west are facing an unprecedented attack by mountain pine beetles. Females burrow into the bark of pines and lay their eggs immediately beneath the bark. When the larvae hatch, the chew extensive tunnels through the phloem. The tunnels destroy thick bands of phloem tissue and fully disconnect the top portion of the tree from the bottom resulting in tree death.

Which of the following accurately describes how destroying the phloem would kill the tree?

Taken from “Whitebark pine (Pinus albicaulis) growth and defense in response to mountain pine beetle outbreaks”

BlackTom AI · Accepted Answer

First, let’s anchor the idea of plant transport: phloem is the vascular tissue responsible for moving sugars (mainly sucrose) from photosynthesizing tissues to other parts of the plant that need energy, such as roots, developing shoots, or storage tissues. 
Option A states that destroying phloem would prevent the transport of sugars from the shoot where they’re produced to the roots. This aligns with the known function of phloem, making it the correct description of the effect. 
Option B claims disruption of water and nutrients movement from roots to shoots; that pathway is primarily the job of xylem, not phloem, so this option misidentifies the transport system involved. 
Option C suggests sugars would be transported from roots to the shoot; in most plants, roots are sinks for sugars rather than primary producers, and phloem movement is typically from shoot (source) to root (sink), not the reverse. Therefore this option is incorrect. 
Option D says sugars would move from the shoot to the roots, which is the correct directional flow, but since the option wording is identical to Option A, the intent is to identify the mechanism correctly; however, the phrasing in D appears to restate the same concept as A in the provided list. The key distinction to focus on is that phloem transports sugars from sources in the shoot to sinks like the roots, not water transport handled by xylem. 
In summary, the only option that correctly describes the consequence of phloem destruction is the one asserting the interruption of sugar transport from the shoot to the roots, which would starve roots and other tissues of energy and lead to death over time.

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