Resource acquisition and transport in plants — A/L Biology

How do I practise Resource acquisition and transport in plants?

1 question with a worked solution

1. According to the pressure-flow hypothesis of phloem translocation, what directly drives the bulk flow of sap from source to sink?
   1. A) Active pumping of sucrose along the sieve plate pores
   2. B) Turgor pressure gradient generated by osmotic water movement
   3. C) Capillary action in sieve tube elements
   4. D) Transpirational pull from the stomata
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   Correct answer: B) Turgor pressure gradient generated by osmotic water movement

   Active loading of sucrose at source cells lowers water potential, causing water to enter by osmosis and generating high turgor pressure. At the sink, sucrose unloading increases water potential, water leaves, and low turgor pressure results. The resulting hydrostatic turgor pressure gradient drives bulk flow.

   Show worked solution

   Step 1: Review Ernst Münch pressure-flow mechanism. Step 2: High sucrose concentration at source → water enters → high hydrostatic pressure. Step 3: Low sucrose concentration at sink → water exits → low hydrostatic pressure. Step 4: Hydrostatic pressure difference drives mass bulk flow of phloem sap. Answer: Turgor pressure gradient generated by osmotic water movement.
   Modelled on: the A/L Biology examination pattern

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Where does Resource acquisition and transport in plants fit in the syllabus?

Year 1 · Term 3