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Difficulty: MediumTransport Mechanisms in Plants

Match each specialized plant structure or transport term on the left with its corresponding physiological function or characteristic on the right.

  • HydathodesExudation of liquid water droplets driven by positive root pressure
  • Companion cellsATP-dependent active loading of sucrose into sieve tube elements
  • Casparian stripSuberized cell wall layer in the endodermis forcing water into the symplastic pathway
  • TranslocationMass flow of organic solutes along hydrostatic pressure gradients from source to sink

Answer

Hydathodes pair with liquid water exudation under root pressure; Companion cells pair with active sucrose loading into sieve tube elements; Casparian strip pairs with the suberized endodermal band blocking apoplastic transport; Translocation pairs with mass flow of organic solutes from source to sink.
Each structure or process is accurately matched: Hydathodes facilitate liquid water exudation (guttation); Companion cells drive active sucrose transport; the Casparian strip acts as an endodermal suberin filter; and Translocation is the bulk transport of organic nutrients in phloem.

Step-by-Step Solution

1
Analyze the function of hydathodes.
Hydathodes mediate guttation, releasing liquid water drops when atmospheric humidity is high and root pressure is elevated.
They are open pore structures at vein terminations, distinct from stomata.
2
Determine the role of companion cells in phloem transport.
Companion cells provide metabolic support and energy for proton-sucrose symport into sieve tubes.
Mature sieve tube elements lack nuclei and require metabolic assistance from adjacent companion cells.
3
Identify the physiological barrier posed by the Casparian strip.
The Casparian strip prevents unregulated solute movement via the apoplast, steering transport into living endodermal protoplasts.
Suberin deposition creates an impermeable ring around radial and transverse endodermal walls.
4
Define translocation in vascular plants.
Translocation is the multi-directional movement of sugar solutions driven by turgor pressure differences described by the pressure-flow hypothesis.
High solute concentration at the source draws water in, creating high hydrostatic pressure relative to the sink.

Key Concept

Plant Transport Mechanisms and Structural Adaptations
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Topics

Transport Mechanisms in Plants

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