Transport in plants (xylem, phloem, transpiration) Knowledge-Based Download PDF

Questions

1. 1.

   Which physiological event directly causes guard cells to become turgid and bow outward, facilitating the opening of stomata for transpiration?

   • A) Passive efflux of potassium ions from guard cells into surrounding epidermal cells
   • B) Conversion of soluble sugars into insoluble starch within the guard cell cytoplasm
   • C) Active accumulation of potassium ions into guard cells, followed by osmotic influx of water
   • D) Rapid synthesis and accumulation of abscisic acid within the guard cell vacuoles
2. 2.

   During the radial transport of water from the soil into the root vascular cylinder, which structural feature forces water and dissolved minerals out of the apoplastic pathway and across a selectively permeable plasma membrane?

   • A) The waxy cuticle of the root epidermis
   • B) The perforated sieve plates of the phloem
   • C) The secondary cell walls of cortical parenchyma
   • D) The suberin-impregnated Casparian strip of the endodermis
3. 3.

   According to the pressure-flow hypothesis of phloem transport, which event directly causes the generation of high hydrostatic pressure inside sieve-tube elements at a source?

   • A) Passive diffusion of water out of sieve-tube elements into adjacent companion cells
   • B) Active transport of potassium ions out of sieve tubes into surrounding parenchyma
   • C) Osmotic influx of water following the active loading of sugars into sieve tubes
   • D) Transpirational pull creating negative tension in neighboring tracheids
4. 4.

   According to the cohesion-tension model of xylem transport, which event provides the primary pulling force for the upward movement of water through a plant stem?

   • A) Active accumulation of mineral ions in root vessels that produces continuous positive root pressure
   • B) Generation of high hydrostatic pressure via the active loading of sucrose at source tissues
   • C) Evaporation of water from the surfaces of leaf mesophyll cells into intercellular air spaces
   • D) Osmotic influx of water caused by potassium ion efflux from guard cells into subsidiary cells
5. 5.

   Which of the following statements correctly distinguishes the structure and transport mechanism of xylem from that of phloem in vascular plants?

   • A) Xylem conducts organic solutes bidirectionally using hydrostatic pressure, whereas phloem transports inorganic ions unidirectionally via bulk flow.
   • B) Xylem vessel elements are living cells that utilize ATP to move water upward, whereas phloem sieve tube elements are dead and passive at maturity.
   • C) Xylem consists of dead cells that transport water and minerals unidirectionally driven by transpiration pull, whereas phloem consists of living cells that translocate sugars bidirectionally between sources and sinks.
   • D) Xylem transport depends on active loading by companion cells at the roots, whereas phloem transport is powered entirely by negative pressure generated by stomatal evaporation.