Translocation in phloemAQA A-Level Biology: Flashcards
What these 13 flashcards ask
- What is translocation?
- Name the two main cell types in phloem.
- Why do companion cells have many mitochondria?
- What is a source?
- What is a sink?
- How is sucrose loaded into companion cells?
- What happens to water when sucrose is loaded into the sieve tube?
- What drives mass flow in the phloem?
- What is the role of sieve plates?
- What does ringing a stem remove?
- What is seen above a ring and why?
- How does a ¹⁴CO₂ tracer experiment show phloem transport?
- Give one piece of evidence against mass flow.
Exam questions on Translocation in phloem
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).