Recap - StarterRecap - StarterState 3 differences between

xylem and phloem structures

State the differences between the symplast and apoplast pathways

Define transpiration and state where does this occurs

Starter – Challenge!Starter – Challenge!X-word on keywords on plant

transport learnt last lesson

8 min

Last Lesson....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

Explain how Explain how translocation happens happens

TaskTaskDescribe how

sucrose moves along the phloem from source to sink using the following keywords:

mass flow water potentialosmosis hydrostatic

pressure

Exam ObjectivesExam 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).

The evidence for translocationThe 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 mitochondriaUse of poison to prevent synthesis of ATPThe rate of flow of sugars is so high that energy

must be needed to drive the flow, rather than diffusion

Evidence for translocationEvidence for translocation

How we know it is Source / sink mechanism:-pH of companion cells is higher than that of

the surrounding cellsElectrical potential difference across

membrane of companion cellsHigher sucrose concentration in the source

than in the sinkEvidence against this mechanismNot all the solutes in the phloem sap move at

the same rateSucrose 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

Homework CheckHomework CheckComplete 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