Plant Carbohydrate Transport Quiz

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6 Questions

What is one advantage of mass flow in transporting organic solutes in plants?

It moves organic solutes faster than diffusion.

Why are carbohydrates generally transported in plants in the form of sucrose?

Sucrose is a disaccharide and contains more energy.

How is the pressure difference that causes mass flow in xylem tissues generated?

By a water potential gradient between the soil and leaf.

What process requires energy input for creating pressure differences in phloem tissue?

Active loading of sucrose into sieve elements.

How does the active loading of sucrose into sieve elements impact water movement?

It lowers water potential in the sap.

Why does the presence of water within the sieve elements increase hydrostatic pressure at the source?

Water exerts osmotic pressure within the sieve elements.

Study Notes

Phloem Sap Transport

  • Phloem sap, containing sucrose and other organic solutes, moves up and down the plant through mass flow.
  • Sucrose is the primary carbohydrate transported in plants due to its:
    • Efficient energy transfer and increased energy storage as a disaccharide.
    • Non-reactive nature as a non-reducing sugar, preventing intermediate reactions during transport.

Mass Flow Advantage

  • Mass flow transports organic solutes faster than diffusion.

Xylem vs. Phloem Transport

  • In xylem tissue, mass flow occurs due to a water potential gradient between the soil and leaf, requiring no energy input from the plant.
  • In phloem tissue, energy is required to create pressure differences for mass flow.

Pressure Difference Generation

  • Pressure difference in phloem tissue is generated by actively loading sucrose into sieve elements at the source (e.g., photosynthesizing leaf or storage organ).
  • This lowers the water potential in the sap, causing water to move into the sieve elements by osmosis.
  • The presence of water in the sieve elements increases the hydrostatic or turgor pressure at the source.

Test your knowledge on how carbohydrates are transported in plants, specifically focusing on the advantages of transporting sucrose compared to glucose. Learn about the efficiency of energy transfer and storage when using sucrose as the main carbohydrate for transportation.

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