TRANSPORT IN THE PHLOEM OF PLANTS Structure and function are correlated in the phloem of plants. AHL Topic 9.2 IB Biology Miss Werba

TOPIC 9 – PLANT BIOLOGY 9.1 9.2 9.3 GROWTH IN PLANTS TRANSPORT IN THE XYLEM OF PLANTS 9.2 TRANSPORT IN THE PHLOEM OF PLANTS 9.3 GROWTH IN PLANTS 9.4 REPRODUCTION IN PLANTS J WERBA – IB BIOLOGY 2

THINGS TO COVER Statement Guidance U.1 U.2 U.3 U.4 U.5 A.1 S.1 S.2 Plants transport organic compounds from sources to sinks. U.2 Incompressibility of water allows transport along hydrostatic pressure gradients. U.3 Active transport is used to load organic compounds into phloem sieve tubes at the source. U.4 High concentrations of solutes in the phloem at the source lead to water uptake by osmosis. U.5 Raised hydrostatic pressure causes the contents of the phloem to flow towards sinks. A.1 Structure–function relationships of phloem sieve tubes. S.1 Identification of xylem and phloem in microscope images of stem and root. S.2 Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-labelled carbon dioxide. NOS 1.8 Developments in scientific research follow improvements in apparatus — experimental methods for measuring phloem transport rates using aphid stylets and radioactively-labelled carbon dioxide were only possible when radioisotopes became available. J WERBA – IB BIOLOGY 3

PHLOEM SIEVE TUBES A.1 The structure of phloem sieve tubes relates to its function. J WERBA – IB BIOLOGY 4

PHLOEM SIEVE TUBES A.1 The structure of phloem sieve tubes relates to it’s function. J WERBA – IB BIOLOGY 5

PHLOEM SIEVE TUBES A.1 Sieve element: conducting element of the phloem;  form tubes to transport water and solutes; have reduced cytoplasm and no nucleus, ribosomes or vacuole Companion Cell: "life support" cell for the sieve element cells;  perform metabolic functions for sieve elements J WERBA – IB BIOLOGY 6

PHLOEM SIEVE TUBES A.1 Fibres: made of sclerenchyma cells; provides structural support for the plant  Parenchyma cells: acts as packing material between other cell types; helps transfer materials to the SE/CC complex  J WERBA – IB BIOLOGY 7

PHLOEM SIEVE TUBES The sieve elements cells have rigid cell walls. This allows high pressure to build up and create flow inside the tube. The ends of sieve element cells are connected to each other. They form a sieve plate with large pores to facilitate the flow of substances between the cells.   J WERBA – IB BIOLOGY 8

TRANSLOCATION U.1 U.2 Translocation: the movement of sugars and amino acids from one part of a plant to another Translocation occurs through the phloem. The fluid in the phloem is called sap. Watch this: http://www.pearsoned.ca/school/science11/biology11/sugartransport.html And this: http://highered.mheducation.com/sites/9834092339/student_view0/chapter 38/animation_-_phloem_loading.html J WERBA – IB BIOLOGY 9

TRANSLOCATION Translocation in the phloem is active U.1 U.2 Translocation in the phloem is active phloem cells have to use energy to make the substances move Sugars and amino acids are loaded into the phloem in parts of the plant called sources... eg. leaves & stems ...and are translocated to sinks, where they are unloaded eg. roots, fruits & seeds J WERBA – IB BIOLOGY 10

ACTIVE TRANSPORT Sucrose is actively transported into the phloem Protons are actively transported out of the phloem cell through a proton pump (using ATP) Proton motive force used to transport sucrose across the membrane, against it’s concentration gradient J WERBA – IB BIOLOGY 11

OSMOSIS High concentrations of sucrose in the phloem cells Results in water moving by osmosis from the xylem to the phloem cells J WERBA – IB BIOLOGY 12

HYDROSTATIC PRESSURE Water is incompressible – has a fixed volume Sieve tubes have rigid cells walls This builds up hydrostatic pressure at the source. Water and solutes will flow down the hydrostatic gradient from the source to the sink. The low pressure near the sink is a result of the active unloading of sucrose & the resultant loss of water. J WERBA – IB BIOLOGY 13

DATA ANALYSIS S.2 Skill: you need to be able to analyse data from experiments measuring phloem transport rates using aphid stylets and radioactively-labelled carbon dioxide. J WERBA – IB BIOLOGY 14

DATA ANALYSIS S.2 Aphids are insects that have evolved the ability to feed on plant sap. Aphid stylet is the piercing / sucking mouthpart that they insert into the phloem to extract the sap. Scientists can cut the stylet after feeding has begun to sample the sap and measure its flow. J WERBA – IB BIOLOGY 15

DATA ANALYSIS Process: Plant grown in presence of radioactively-labelled CO2 (carbon-14) Plant uses CO2 to make glucose. Glucose is converted into sucrose for translocation via the phloem. Aphids are encouraged to feed on the phloem at different points along the stem. The phloem is then analysed for carbon-14. J WERBA – IB BIOLOGY 16

Developments in scientific research follow improvements in apparatus DATA ANALYSIS S.2 NOS 1.10 Developments in scientific research follow improvements in apparatus Experimental methods for measuring phloem transport rates were only possible when radioisotopes (carbon-14) became available. J WERBA – IB BIOLOGY 17

TRANSPORT IN PHLOEM Q1. When a farmer sprays a chemical on to crop plants, how does the chemical travel to the roots of the plants? In the phloem, by active translocation In the phloem, by transpiration pull In the xylem, by transpiration pull In the xylem, by active translocation J WERBA – IB BIOLOGY 18

TRANSPORT IN PHLOEM Q2. Which direction does the phloem transport materials? Up the plant at night and down the plant during the day Up and down the plant all the time Up the plant only Down the plant only J WERBA – IB BIOLOGY 19

TRANSPORT IN PHLOEM Q3. Outline the role of the phloem in the active translocation of biochemicals. [5] J WERBA – IB BIOLOGY 20