1. Recap - Starter State 3 differences between xylem and phloem structures State the differences between the symplast and apoplast pathways Define transpiration and state where does this occurs

2. Starter – Challenge! X-word on keywords on plant transport learnt last lesson 8 min

3. Last Lesson.... Movement of water in plant cells Movement of water through the plant Movement of assimilates (sugars and other chemicals made by the plant cell) by translocation

4. Explain how translocation happens translocation

5. Task Describe how sucrose moves along the phloem from source to sink using the following keywords: mass flow water potential osmosis hydrostatic pressure

6. Exam Objectives Describe, with the aid of diagrams, the mechanism of transport in phloem involving active loading at the source and removal at the sink, and the evidence for and against this mechanism (HSW1, 7a).

7. The evidence for translocation How we know phloem used for movement of sucrose:- Use of radioactively labelled carbon dioxide (which will be used in photosynthesis), the labelled carbon soon appears in the phloem Ringing tree to remove phloem results in sugars collecting above the ring Aphid feeding on plant stem, mouthparts are taking food from the phloem How we know energy from ATP needed for translocation:- Companion cells have many mitochondria Use of poison to prevent synthesis of ATP The rate of flow of sugars is so high that energy must be needed to drive the flow, rather than diffusion

8. Evidence for translocation How we know it is Source / sink mechanism:- pH of companion cells is higher than that of the surrounding cells Electrical potential difference across membrane of companion cells Higher sucrose concentration in the source than in the sink Evidence against this mechanism Not all the solutes in the phloem sap move at the same rate Sucrose is moved to all parts at the same rate, rather than going more quickly to areas with alow concentration The role of sieve plates is unclear

9. Homework Check Complete plant transport booklet pages 5, 6, 7 Try some practice exam Qs Revise for Mock exams for Monday and Thursday next week on all of F211 – Use Moodle to do practice exam Qs and revision activities