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Plant Water Relation — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYPlant Water Relation5 Marks
Question
Explain mechanism of sugar transport through phloem.
✓

Answer

  1. The part of plant where food is synthesized is known as source and where it is utilized is sink.
  2. Food is translocated through phloem tissue in the form of sucrose along the concentration gradient from source to sink.
  3. Munch’s pressure flow theory or mass flow hypothesis is widely accepted theory for sugar transport.
  4. Glucose is synthesized in photosynthetic cells hence endo-osmosis occurs due to increased osmotic concentration.
  5. With this turgor pressure increases and sugar is forced in sieve tube of vein from photosynthetic cell – Vein loading.
  6. At the sink, sugar is utilized and excess amount converted to starch, hence osmotic concentration is lowered and exosmosis takes place.
  7. Turgor pressure is lowered hence turgor pressure gradient is set and food is translocated passively against concentration gradient – Vein unloading.

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