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AS Biology UNIT F Transport in Plants

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1 AS Biology UNIT F211 1.2.3 Transport in Plants
Amy Dicksee E – mail:

2 Starter – less than 10 min Can you state 3 ways in which xylem vessels are adapted for their function?

3 Exam Objectives Describe with the aid of diagrams and photographs the structure and function of xylem vessels, and phloem sieve tube elements and companion cells

4 Xylem in young stems – what is the strengthening made from?
Spirals, rings or broken rings. Provide……….. Strength, no collapsing, flexibility

5 Xylem Why pits and perforations?

6 Xylem Carries water from the roots to the rest of the plant

7 Explain Capillarity….. Cohesion of water molecules!
See Information Sheet

8 Xylem How 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!

9 Write a paragraph to show you understand the adaptations of xylem to its function….share with you partner, add to your notes tissue support transport of water lignin strong / resists tension impermeable to water no cytoplasm or nucleus less resistance to or end walls water movement pits vessels adhesion capillarity

10 Looking 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

11 Phloem Function : Transports sugars from one part of the plant to another. Transport can be up or down the stem Structure: 2 types of cells Sieve tube elements Companion cells

12 Sieve tubes and companion cells

13 Phloem Why are they called Sieve tubes? ‘Semi’ empty.
Have sieve plates to allow sap to flow. What is SAP?

14 Why do we have companion cells?
Sieve tube elements are alive, but have no nucleus, few organelles and only strands of cytoplasm Have to be aided by companion cells which respire, excrete, etc. on their behalf Cytoplasm of the companion cells and sieve tube element is joined through pores in side walls Contain many Mitochondria to provide ATP for loading!

15 Stop 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 table Complete page 4 of your booklet. Ext: read : how trees lift water XYLEM PHLOEM (sieve tube) Tubular Vessel Living Transports sugars One way flow No contents End walls adapted as sieve plates No companion cell

16 Comparing xylem and phloem
make a table and draw diagrams to compare and contrast the following features:- function names of the cells are the cells living or dead? molecules transported direction of transport molecules in cell walls end walls between cells cell contents Pages 44 and 45 Revision Guide

17 Next objective Movement of water in plant cells
Movement of water through the plant

18 Exam Objective Explain, in terms of water potential, the movement of water between plant cells, and between plant cells and their environment

19 Water always moves from a region of
Water Potential (ψ) recap…finish these sentences with a white board/ scrap paper- discuss with your partner Water always moves from a region of higher water potential to a region of lower water potential Pure water has a water potential of zero In a plant cell, the cytoplasm contains dissolved salts and sugars (solutes) that will reduce the water potential As a result water potential in plant cells is always negative Water molecules move from less negative regions (higher water potential) to more negative regions (lower water potential) If you want to recap these notes 72 of new book: come to me for PC

20 Recap 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?

21 So 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

22 Movement of water….getting to the Xylem

23 Movement of water between cells
When plant cells are touching each other, water molecules can pass from one cell to another Water 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 salts Symplast pathway –passes through cytoplasm Vacuolar pathway (water able to pass through cytoplasm and vacuole)

24 Draw the routes taken by water from a root hair to the xylem.

25 Movement through the Roots
and Plasmadesmata Movement through the Roots


27 Lesson 2

28 This needs to be in on Monday
HLA: start in class Read 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 from The soil into the root hair The root hair into the xylem Up through the Xylem vessels From the leaf into the air This 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 Pathway This needs to be in on Monday

29 Starter – Key Definitions
Cohesion Is the attraction of water molecules to one another- due to intermolecular forces / hydrogen bonds Adhesion Is the attraction of water molecules to the walls of the xylem Symplast pathway Water moving through the cell cytoplasm Apoplast pathway Water moving via the cell walls and between the cells Casparian strip Stip of waterproof material (suberin) in walls of root epidermal cells. Blocks the apoplast pathway forcing water to the symplast pathway Transpiration The loss of water vapour from the arial parts of a plant due to evaporation

30 Do we get this diagram of a leaf section?

31 Water diffuses from the xylem into the spaces inside the spongy mesophyll--> stoma-->atmosphere. This drives the Transpiration Stream

32 Water 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 air Relate this to the leaf overview sheet given out last week

33 Exam 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 stomata Explain 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

34 So lets recap/ complete the transpiration stream
er_movement.htm (link to animation of transpiration) Water moves up the stem due to…. Root pressure Transpiration pull Capillary action

35 Apoplast and Symplast Pathways

36 The 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.

37 So: 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?


39 Rise of water up the Xylem

40 Transpiration Pull Once water reaches the xylem it moves upwards as a result of transpiration Transpiration is the loss of water from the aerial parts of the plant (particularly from the stomata in the leaves) as a result of evaporation The evaporation of water from the top of the plant creates a pulling force drawing the water up the xylem This pulling force is called tension The water molecules are strongly attracted to each. This is called cohesion So the two forces together give us the cohesion-tension model for the movement of water in xylem 


42 Demonstrate Complete pages 5 and 7 in work booklet
Extension: Answer questions on back of Water Movement in Plants Ensure you have all your key words done:

43 Q. 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!!!!

44 Transpiration and factors affecting it.
About 99% of all water entering the roots is lost via transpiration A single plant can transpire about 60L of water in a single growing season Survival of the plant depends on balancing the uptake and loss of water

45 Exam Objective Define the term transpiration
Explain why transpiration is a consequence of gaseous exchange Describe the factors that affect transpiration

46 Exam Objective Describe, with aid of diagrams, how a potometer is used to estimate transpiration See Handout

47 Transpiration Involves... (Copy?)
Osmosis from the xylem to the mesophyll cells Evaporation from the surface of the mesophyll cells into the intercellular spaces Diffusion of water vapour from the intercellular spaces out through the stomata

48 Water Losses The loss of water by transpiration is unavoidable
Plant exchange gases with the atmosphere via their stomata

49 Transpiration stream Is the continuous movement of water from the roots up through the xylem into the leaves, and out to atmosphere

50 Evaporation is endothermic and is driven by solar energy, which is therefore the ultimate source of energy for all the water movements in plants:

51 RATE OF TRANSPIRATION Is driven by evaporation at the leaf and the water potential gradient

52 In today’s lesson... Overview of the movement of water through the plant and transpiration Factors that affect transpiration How to use a potometer to estimate transpiration rates Practice for the next assessed practical

53 Factors effecting transpiration
Hand-out sheet – work in pairs just to discuss 5 mins


55 Video on Experiment 4Q2NxiNE&feature=endscreen&NR=1

56 Task 2: Copy the table and fill using books
Factors that affect the rate of water loss How it affects water loss Task – use Page 48 Revision Guide /pg 98 Green OCR Draw diagram of potometer Outine how it is set up Describe what it does Complete page 14 / 15 Complete q 2, 3 and 4 in booklets: exam questions peer mark with answer booklets

57 Exam Practice Complete q 2, 3 and 4 in booklets: exam questions peer mark with answer booklets

58 Explore the concept of how to use a potometer to measure transpiration rate using this web site
_place/labbench/lab9/design.html Work through the explanations/ animations /tasks and use it to outline an experiment you would plan


60 Measuring the rate of transpiration from a stem

61 Actually 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.

62 the 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 mins Method the independent variable and how to change it the dependent variable and how to measure it the controlled factors and how to control them What 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?)

63 Describe briefly how you would set the equipment up to estimate the pattern of transpiration over 30 minutes in two different species of plant.

64 HLA : Xerophytes Make notes on adaptations of Xerophytes and draw outline diagram of Marram grass to show adaptations Go onto Moodle F211 Specimen Paper; Do potometer question (5) (pages 12-14) Mark against mark scheme :true evaluation please!

65 They 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 photosynthesis They must also remove oxygen which is by- product of photosynthesis So the stomata must be open during the day While they are open, there is an easy route for the water to be lost HOW 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


67 Homework The root hairs of a plant and the alveoli of the lungs are exchange surfaces What molecules or ions are involved? Describe the features the root hairs and alveoli have in common

68 Plant Cells and their Environment
Can you explain what is happening to the cells in terms of water potential and osmosis?

69 Transpiration Review z4HHk

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