6XylemCarries water from the roots to the rest of the plant
7Explain Capillarity….. Cohesion of water molecules! See Information Sheet
8XylemHow does it’s structure enable the transport of water from the root to the leaf Dead cell + hollow to…… Thin to…… Pits to….. Lignified walls to… The movement of water is not impeded!
9Write a paragraph to show you understand the adaptations of xylem to its function….share with you partner, add to your notestissue support transport of waterlignin strong / resists tension impermeable to waterno cytoplasm or nucleus less resistance to or end walls water movementpitsvesselsadhesioncapillarity
10Looking at xylem vessels Place one Bizzie Lizzie leaf stem on microscope slide on a folded paper towel.Add 2 drops conc hydrochloric acid (care).Then 2 drops phloroglucinol (care).Place 2 coverslips side by side over stem and fold paper towel over the top.Press gently sideways to squash out and flatten tissues along stem.Observe xylem tissue under microscope
11PhloemFunction : Transports sugars from one part of the plant to another. Transport can be up or down the stemStructure: 2 types of cellsSieve tube elementsCompanion cells
13Phloem Why are they called Sieve tubes? ‘Semi’ empty. Have sieve plates to allow sap to flow.What is SAP?
14Why do we have companion cells? Sieve tube elements are alive, but have no nucleus, few organelles and only strands of cytoplasmHave to be aided by companion cells which respire, excrete, etc. on their behalfCytoplasm of the companion cells and sieve tube element is joined through pores in side wallsContain many Mitochondria to provide ATP for loading!
15Stop and recap, demonstrate Why …….Are the sieve tube not ‘true cells’?Why do they only contain a thin layer of Cytoplasm?Copy and complete this tableComplete page 4 of your booklet.Ext: read : how trees lift waterXYLEMPHLOEM (sieve tube)Tubular VesselLivingTransports sugarsOne way flowNo contentsEnd walls adapted as sieve platesNo companion cell
16Comparing xylem and phloem make a table and draw diagrams to compare and contrast the following features:-functionnames of the cellsare the cells living or dead?molecules transporteddirection of transportmolecules in cell wallsend walls between cellscell contentsPages 44 and 45 Revision Guide
17Next objective Movement of water in plant cells Movement of water through the plant
18Exam ObjectiveExplain, in terms of water potential, the movement of water between plant cells, and between plant cells and their environment
19Water always moves from a region of Water Potential (ψ) recap…finish these sentences with a white board/ scrap paper- discuss with your partnerWater always moves from a region ofhigher water potential to a region of lower water potentialPure water has a water potential ofzeroIn a plant cell, the cytoplasm contains dissolved salts and sugars (solutes) that willreduce the water potentialAs a result water potential in plant cells is always negativeWater molecules move from less negative regions (higher water potential)to more negative regions (lower water potential)If you want to recap these notes ..page 72 of new book: come to me for PC
20Recap Transport Question A pair of adjacent cells, A and B, have water potentials of and kPa, respectively.Which cell will gain water from the other?
21So how do water and mineral ions reach the xylem in the root So how do water and mineral ions reach the xylem in the root? Root Hairs
23Movement of water between cells When plant cells are touching each other, water molecules can pass from one cell to anotherWater molecules will move from the cell with the higher water potential (less negative value) to the cell with the lower water potential (more negative)3 pathways that water molecules can take between cells:Apoplast pathway – can also carry dissolved minerals and saltsSymplast pathway –passes through cytoplasmVacuolar pathway (water able to pass through cytoplasm and vacuole)
24Draw the routes taken by water from a root hair to the xylem.
25Movement through the Roots and PlasmadesmataMovement through the Roots
28This needs to be in on Monday HLA: start in classRead page the book online (sounds a lot but lots of diagrams!) or (page may need to refer to page 73 as well)Write notes (at least 1 ½ pages long) summarising the journey of water fromThe soil into the root hairThe root hair into the xylemUp through the Xylem vesselsFrom the leaf into the airThis will take you at least an hour. Draw diagrams etc .to help explanations. Use page 6 as a guide.Key words : Transpiration, Cohesion, Symplast Pathway, Plasmodesmata, Apoplast PathwayThis needs to be in on Monday
29Starter – Key Definitions CohesionIs the attraction of water molecules to one another- due to intermolecular forces / hydrogen bondsAdhesionIs the attraction of water molecules to the walls of the xylemSymplast pathwayWater moving through the cell cytoplasmApoplast pathwayWater moving via the cell walls and between the cellsCasparian stripStip of waterproof material (suberin) in walls of root epidermal cells. Blocks the apoplast pathway forcing water to the symplast pathwayTranspirationThe loss of water vapour from the arial parts of a plant due to evaporation
31Water diffuses from the xylem into the spaces inside the spongy mesophyll--> stoma-->atmosphere. This drives the Transpiration Stream
32Water movement from xylem in root to air around leaves add labels to the leaf diagram (link to diagram)draw arrows to show the path of a water molecule from xylem in leaf vein to airRelate this to the leaf overview sheet given out last week
33Exam Objectives: have we addressed these? Describe, with the aid of diagrams, the pathway by which water is transported from the root cortex to the air surrounding the leaves, with reference to the Casparian strip, apoplast pathway, symplast pathway, xylem and stomataExplain the mechanism by which water is transported from the root cortex to the air surrounding the leaves, with reference to adhesion, cohesion and the transpiration stream
34So lets recap/ complete the transpiration stream er_movement.htm (link to animation of transpiration)Water moves up the stem due to….Root pressureTranspiration pullCapillary action
36The water potential gradient is maintained by the movement of water away up the Xylem and by the active transport of minerals at the ……………….. and the ………………… The movement of water onto the Xylem like this provides an upwards pushing ROOT PRESSURE.
37So: stop and recap What is root pressure? Does root pressure provide enough push to move water far up the Xylem?What type of environment would root pressure play a more important role in?
40Transpiration PullOnce water reaches the xylem it moves upwards as a result of transpirationTranspiration is the loss of water from the aerial parts of the plant (particularly from the stomata in the leaves) as a result of evaporationThe evaporation of water from the top of the plant creates a pulling force drawing the water up the xylemThis pulling force is called tensionThe water molecules are strongly attracted to each. This is called cohesionSo the two forces together give us the cohesion-tension model for the movement of water in xylem
42Demonstrate Complete pages 5 and 7 in work booklet Extension: Answer questions on back of Water Movement in PlantsEnsure you have all your key words done:
43Q. What does the tension created by the transpiration stream have to do with lignified walls? Lignin prevents the vessel from collapsing under the tension created.Trees do go thinner when transpiring!!!!
44Transpiration and factors affecting it. About 99% of all water entering the roots is lost via transpirationA single plant can transpire about 60L of water in a single growing seasonSurvival of the plant depends on balancing the uptake and loss of water
45Exam Objective Define the term transpiration Explain why transpiration is a consequence of gaseous exchangeDescribe the factors that affect transpiration
46Exam ObjectiveDescribe, with aid of diagrams, how a potometer is used to estimate transpirationSee Handout
47Transpiration Involves... (Copy?) Osmosis from the xylem to the mesophyll cellsEvaporation from the surface of the mesophyll cells into the intercellular spacesDiffusion of water vapour from the intercellular spaces out through the stomata
48Water Losses The loss of water by transpiration is unavoidable Plant exchange gases with the atmosphere via their stomata
49Transpiration streamIs the continuous movement of water from the roots up through the xylem into the leaves, and out to atmosphere
50Evaporation is endothermic and is driven by solar energy, which is therefore the ultimate source of energy for all the water movements in plants:
51RATE OF TRANSPIRATIONIs driven by evaporation at the leaf and the water potential gradient
52In today’s lesson...Overview of the movement of water through the plant and transpirationFactors that affect transpirationHow to use a potometer to estimate transpiration ratesPractice for the next assessed practical
53Factors effecting transpiration Hand-out sheet – work in pairs just to discuss5 mins
55Video on Experiment4Q2NxiNE&feature=endscreen&NR=1
56Task 2: Copy the table and fill using books Factors that affect the rate of water lossHow it affects water lossTask – use Page 48 Revision Guide /pg 98 Green OCRDraw diagram of potometerOutine how it is set upDescribe what it doesComplete page 14 / 15Complete q 2, 3 and 4 in booklets: exam questions peer mark with answer booklets
57Exam PracticeComplete q 2, 3 and 4 in booklets: exam questions peer mark with answer booklets
58Explore the concept of how to use a potometer to measure transpiration rate using this web site _place/labbench/lab9/design.htmlWork through the explanations/ animations /tasks and use it to outline an experiment you would plan
61Actually measures the rate of water uptake by the cut stem, not the rate of transpiration; and these two are not always the same. During the day plants often transpire more water than they take up (i.e. they lose water and may wilt), and during the night plants may take up more water than they transpire (i.e. they store water and become turgid). The difference can be important for a large tree, but for a small shoot in a potometer the difference is usually trivial and can be ignored.
62the independent variable and how to change it Outline an experiment that you would set up to measure the effect of differenty environmental conditions on transpiration rate using a potometer: 30 minsMethodthe independent variable and how to change itthe dependent variable and how to measure itthe controlled factors and how to control themWhat type of graph would you draw?Evaluation What are the limitations of using a potometer to measure the rate of transpiration? (Hint: What is the definition of transpiration? Does a potometer measure this?)
63Describe briefly how you would set the equipment up to estimate the pattern of transpiration over 30 minutes in two different species of plant.
64HLA : XerophytesMake notes on adaptations of Xerophytes and draw outline diagram of Marram grass to show adaptationsGo onto Moodle F211 Specimen Paper; Do potometer question (5) (pages 12-14)Mark against mark scheme :true evaluation please!
65They must also remove oxygen which is by- product of photosynthesis During the day, plants take up a lot of carbon dioxide and use it in photosynthesisThey must also remove oxygen which is by- product of photosynthesisSo the stomata must be open during the dayWhile they are open, there is an easy route for the water to be lostHOW COULD THEY REDUCE TRANSPIRATION?Most plants can reduce these losses by structural and behavioural adaptation i.e. close stomata at night, waxy cuticle, stomata on under surface of leaves