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Difficulty: HardTransport Mechanisms in Plants

Match each plant transport mechanism or pathway in Column A with its corresponding physiological process or driving force in Column B.

  • Transpiration pullUnidirectional ascent of water driven by leaf evaporation and water molecule cohesion
  • Active translocationHydrostatic pressure gradient generated by energy-dependent sucrose loading into phloem
  • Root pressurePositive osmotic pressure in root xylem resulting in guttation through hydathodes
  • Symplast pathwayMovement of water and mineral ions through living cytoplasm connected by plasmodesmata

Answer

Transpiration pull pairs with unidirectional water ascent driven by evaporation and cohesion; Active translocation pairs with hydrostatic pressure gradients generated by energy-dependent sucrose loading; Root pressure pairs with positive osmotic pressure resulting in guttation; Symplast pathway pairs with movement of water and ions through cytoplasm connected by plasmodesmata.
Each mechanism is accurately paired with its primary driver: Transpiration pull drives mass xylem flow via cohesion-tension; Active translocation drives phloem transport via pressure gradients; Root pressure causes guttation via active ion pumping; Symplast pathway conducts water through living cytoplasm via plasmodesmata.

Step-by-Step Solution

1
Analyze the primary tension mechanism in xylem transport.
Transpiration pull relies on evaporative water loss at stomata and cohesive attraction between water molecules for mass flow upward.
This establishes the main driving force for bulk water transport against gravity.
2
Analyze the energy requirement and direction of phloem transport.
Active translocation involves ATP-driven loading of organic nutrients, establishing high pressure at source tissues relative to sink tissues.
Sugar movement in phloem is bidirectional and requires metabolic energy.
3
Examine positive hydrostatic forces in roots under low transpiration conditions.
Active mineral absorption into root xylem cells builds positive root pressure, causing liquid water loss through hydathodes (guttation).
Root pressure acts as a pushing force, distinct from cohesive tension pull.
4
Identify the cellular pathway that crosses cytoplasm.
The symplast pathway utilizes intracellular movement through living cell cytoplasm connected by cytoplasmic strands known as plasmodesmata.
This contrasts with the apoplast pathway, which moves water exclusively through non-living cell wall spaces.

Key Concept

Plant Transport Mechanisms and Vascular Pathways
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Topics

Transport Mechanisms in Plants

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