Translocation in phloemAQA A-Level Biology: Mind map

Exam questions on Translocation in phloem

1. A potato plant makes sugars in its leaves during the summer. Over the same period its underground tubers swell with stored starch, while the shoot tips continue to grow.
   Explain why the concentration of sucrose in the phloem is higher in the leaves than in the tubers.2 marks
2. In a sugar beet plant, sucrose made in the leaves is moved to the storage root through sieve tube elements. Each sieve tube element has a companion cell beside it.
   Explain why the hydrostatic pressure in the sieve tube elements is higher in the leaf than in the storage root.2 marks
3. Two students investigated transport in a woody shrub in summer. Student A removed a complete ring of bark, including the phloem but leaving the xylem intact, from one stem and observed it for two weeks. Student B supplied one leaf on a similar shrub with air containing radioactively labelled carbon dioxide (¹⁴CO₂) for 30 minutes. After 24 hours she cut thin sections of the stem and placed them against X-ray film.
   Explain the changes Student A would observe in the stem, above and below the ring, over two weeks.3 marks