This document provides an overview of resource acquisition and transport in vascular plants. It describes the three scales of transport as (1) individual cells, (2) short-distance transport between tissues and organs, and (3) long-distance transport throughout the plant via xylem and phloem. Key mechanisms discussed include the proton pump, osmosis, water potential, and co-transport. Long-distance transport occurs via transpiration pull, where water is pulled up from the roots to the leaves through the xylem due to transpiration and cohesion-tension.

1. BIO 304
Objective: At the end of this section
the student will be able to:
describe resource acquisition and
modes of transport in vascular plants

2. Students will be able to:
• Describe 3 scales of transport in plants and
explain the mechanisms
• Describe the mechanism of the proton pump
and explain examples of where it is used
• Describe the process of osmosis and be able
to use water potential terminology correctly
• Analyse data and perform calculations about
water potential

3. A1 The 3 scales of transport in plants
1) transport of water and solutes by individual
cells, such as root hairs.
2) short–distance transport of substances from
cell to cell at the levels of tissues and organs,
e.g. such as the loading of sugar into the
sieve tubes of the phloem.
3) long–distance transport within xylem and
phloem at the level of the whole plant

4. Revise!
You know that:
• Water and minerals are transported in
•Sucrose solution and other substances are
transported in

5. An important mechanism: the proton
pump
• “flow” of H+
can do work
• makes the inside of cell negative relative to the outside.
This voltage is a membrane potential

6. Proton pump

7. A2:How the energy can be used
• The membrane potential generated by proton
pumps contributes to the uptake of K+
by root
cells.
• K+
is attracted to negative charge inside
Uses of K+
Control opening of stomata
Activation of enzymes
Involved in production of ATP

8. Cotransport of anions
• ‘downhill passage’ of (H+
is coupled to the
‘uphill’ passage of another for example NO3
−
)
Downhill means with the
concentration gradient,
from high conc to low
Uphill means against the
concentration gradient
Downhill means with the
concentration gradient,
from high conc to low
Uphill means against the
concentration gradient

9. Co-transport

10. Cotransport of solutes
• membrane protein cotransports sucrose with
the H+
that is moving down its gradient, for
example loading into phloem
They are
complementary
to the shape of
the molecule
entering
They are
complementary
to the shape of
the molecule
entering

11. Another example of co-transport

12. A mechanism for transport, and
examples of substances
• NTROOP MPUP
• ONASNI
• TOLESSU
• SNOTACI
• PROTON PUMP
• ANIONS
• SOLUTES
• CATIONS

13. A 3 OSMOSIS
• Osmosis is the movement of water through a
partially permeable membrane
from a HIGH to a LOW WATER POTENTIAL.

14. Demonstrating osmosis
A) TAP WATER
B) SALT WATER
CUCUMBER

15. Cucumber experiments
• Two plastic cups of water
• Into one, add a spoonful of salt- stir to
dissolve.
• Cut 2 thin slices of cucumber
• Add one to each cup. Leave for 15mins.
• Remove cucumber. Observe what has
happened.

16. Water movement- Osmosis

17. A4 Osmosis and red blood cells
External
solution has
LOWER water
potential:
water moves
OUT
External
solution has
LOWER water
potential:
water moves
OUT
External
solution has
HIGHER water
potential:
water moves
IN
External
solution has
HIGHER water
potential:
water moves
IN

18. http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

19. A5 Explain what has happened to the
plant cell
No net water
movement. The ψ is
equal in and out.
Water has entered.
The water potential
is higher outside
Water has left. The
water potential is
higher inside

20. A6 Turgid or Flaccid?
• A cell is turgid when it is full of water- the
water potential is higher outside
• Flaccid means the plant has wilted. Water
has moved out of the cells.
• If a lot of water has moved out they are
plasmolysed. The cell membrane comes away
from the cell wall.

21. Turgid or plasmolysed? Explain

22. Turgid or plasmolysed? Explain

23. A7 Water potential equation
Water potential = solute potential + pressure
potential
ψ = ψs +ψp

24. A 8 Quantifying water potential
• The solutes bind water molecules.
• Number of free water molecules is reduced.
• This lowers capacity of water to do work.
• So it lowers the water potential
• ψS of a solution is always negative
• 0.1 M solution of a sugar, for example, has a
ψS of −0.23 MPa.

25. A9 There will now
be no net flow of
water between this
pressurized
solution and the
compartment of
pure water. The
levels are the same
A negative pressure
(tension)of −0.30
MPa on the water
compartment
would draw water
from the solution
that has a water
potential of −0.23
MPa
this
solution
will lose
water to
one
containing
pure water.

26. A turgid plant

27. A flaccid plant

28. A turgid plant

29. Since the external solution has the lower
(more negative) water potential, water will
leave the cell by osmosis, and the cell s′
protoplast will plasmolyse, or shrink and pull
away from its wall.
The cell has a lower water potential than
pure water because of the presence of
solutes; water enters the cell by osmosis.
Cell contents swell and press the plasma
membrane against the cell wall producing
turgor pressure. The wall pushes back
against the pressurized cell. Eventually
wall pressure stops the entry of water;
ψP and ψS are equal and ψ = 0
A dynamic equilibrium has been
reached, and there is no further
net movement of water.

30. Check understanding…
If ΨP = 0.3 MPa and ΨS = -0.45 MPa, the
resulting Ψ is _________
• A) +0.75 MPa.
• B) -0.75 MPa.
• C) -0.15 MPa.
• D) +0.15 MPa.
• E) -0.42 MPa.

31. The value for Ψ in root tissue was found to be -0.15
MPa. If you take the root tissue and place it in a 0.1
M solution of sucrose (Ψ = -0.23 MPa), the net
water flow would ______
A)be from the tissue into the sucrose solution.
B) be from the sucrose solution into the tissue.
C) be in both directions and the concentrations would remain
equal.
D) occur only as ATP was hydrolyzed in the tissue
E) be impossible to determine from the values given here.

32. Reminder: membrane
structure=phospholipid bilayer

33. Aquaporin protein

35. A11 Cell compartments
• Cytosol- connected to next cell by
plasmodesmata
• Vacuole – membrane (tonoplast) controls
passage of solutes between cytosol and
vacuole
• Cell walls- allow free passage of water and
solutes

36. A11 Short distance/ lateral transport
• Symplast route - continuous pathway through
cytosolic compartments of adjacent cells.
Connected by plasmodesmata.
• Apoplast - pathway through cell walls and
extracellular spaces.
• Transmembrane route-substances move out
of one cell, across the cell wall, and into the
next cell,

37. Mechanisms/Processes and
Pathways
• Movement of water is
by _____________
• From high ___________
to _______
________
• Pathways are via cell
walls =___________
• Through cytoplasm =
_______________
• Or through membranes
= _____________
osmosis
water potential
water potential
low
apoplast
symplast
transmembrane
Example: If an exam question says-
“Describe the mechanism by which water
enters a plant” - how do you start the
answer?

38. Which way will water move in these plant
cells?
-0.50 MPa-0.50 MPa-0.56 MPa-0.56 MPa
-0.32 MPa-0.32 MPa
In soil ψ = -0.20 Mpa

39. Which plant has cells which will survive
when soil is flooded with sea water? Why?
Plant A
-0.66 MPa
Plant A
-0.66 MPa
Plant B
-0.15 MPa
Plant B
-0.15 MPa
soil flooded with salt
water ψ = -0.55
Mpa
Plant A survives: water
potential outside is
higher, so water goes IN.
Plant B will die- water
potential inside is higher,
water will be lost
Plant A survives: water
potential outside is
higher, so water goes IN.
Plant B will die- water
potential inside is higher,
water will be lost

40. From soil to xylem

42. Remember….
describe the mechanism and the pathway
by which water moves from soil to the
xylem of a plant.
• With a partner- Use keywords to answer the
question above.
• 5 minutes

43. A12 Movement of water and mineral
salts from soil to xylem
• Enter plant through epidermis of roots
by osmosis and mineral salts by active transport
• Cross root cortex by apoplast, symplast or
transmembrane route
• Pass into vascular cylinder through endodermal
cell
• Casparian strip prevents flow through apoplast
• Forces substances into symplast route.
• Then enters xylem vessels and tracheids

44. A13
• Cortical cells are important because if water
travels in the apoplast route, it increases the
surface area available for uptake into the
symplast.

45. A14The fungal hyphae provide an extensive surface area for the absorption
of water and minerals and enable older regions of roots, far from the root
tips, to supply water and minerals to the plant.
Mycorrhiza

46. Movement of water up the plant

47. Bulk flow and long distance transport
A15 Root pressure –
• does not raise water high enough
• not all plants make root pressure
•In the daytime, transpiration is faster than root
pressure.
The main hypothesis for xylem = transpiration
pull and cohesion-tension.
Water is PULLED up

48. Guttation- water droplets forced out
by root pressure

49. A16 Transpirational pull
1. Water vapour diffuses out through stoma- air
outside has a lower ψ
2. Water evaporates from cellulose of leaf
mesophyll cells
3. Surface tension on the cell walls increases
4. Water moves down water potential gradient
5. Tension is transmitted to xylem, and down
the plant. Water molecules are attracted to
each other by cohesion.

50. Transpiration

52. A17 Cohesion –Adhesion -
Tension
• Cohesion of water due to hydrogen bonding
• Column of sap can be pulled from above without
the water molecules separating.
• Water molecules leaving the xylem pull on
adjacent water molecules
• Pull is relayed down the entire column of water
in the xylem
• Adhesion of water molecules ( hydrogen bonds)
to the hydrophilic walls of xylem cells helps

53. A18 Strengthening the xylem
• Cell walls thickened with lignin

54. Sapere Aude!
Dare to think for
yourself!
Dare to be wise!
Have courage to use
your own
understanding

55. Test your understanding
i) Describe the changes in flow
rate between 0600 and 2200
hours
ii) Explain what causes the change
in flow rate between 0600 and
1400 hours
iii)

57. Movement of water in xylem
• file:///Volumes/Campbell
%20Biology/medialib/assets/interactivemedia
/activities/H36/H3601/st01/frame.html

58. A19 Transpiration: wilting and cooling
• Transpiration is fastest when sunny, warm,
dry, and windy
• Some evaporation even when stomata close
• leaves begin to wilt as cells lose turgor
pressure
• Causes evaporative cooling; lowers
temperature of a leaf by 10–15°C. Prevents
denaturing of enzymes

59. Active transport of
H+
out of the guard
cell.
The resulting
voltage
(membrane
potential) drives K+
into the cell
through specific
membrane
channels

60. A20 Regulating turgor in guard cells
Depends on movement of potassium ions (K+
) in
or out of the guard cells.
• guard cells actively take up K+
from epidermal
cells
• water potential becomes more negative
• water enters by osmosis.
• cells become more turgid
• stomata open

61. 12345 WATER TRANSPORT: can you name-
1 type of tissue which transports water and
minerals
2 pathways by which water crosses the cortex of a
root
3 factors which speed up the rate of transpiration
4 structural features of xylem which adapt it to its
function
5 Terms connected with the movement of water
up to the leaves

62. Which statement about proton pumping
across the plasma membrane of plants is
not true?
A.It requires ATP. B. The region inside the
membrane becomes positively charged with
respect to the region outside.
C. It enhances the movement of K+ ions into the
cell.
D. It pushes protons out of the cell against a
proton concentration gradient.
E. It can drive the secondary active transport of
negatively charged ions.

63. Translocation: the pressure flow
model
http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591497__

64. Translocation: bulk transport in the
phloem. Sources and sinks

65. Loading of sucrose into sieve tube cells

67. Pressure-flow

68. A22
• Proton pump removes H ions
• Creates membrane potential
• H ions flow back into companion cell
• Bring sucrose by co-transport
• Sucrose solution diffuses into sieve tube cell

69. A23 The pressure-flow hypothesis
• file:///Volumes/Campbell
%20Biology/medialib/assets/interactivemedia
/activities/H36/H3602/st01/frame.html

70. Evidence for transport in phloem-
composition of sap

71. Evidence for transport in phloem
• Aphid feeding
• Aphid anaesthetised
• Body cut off
• Contents of phloem
collected and analysed

72. Contents of phloem
What is the %
sucrose in the
total solution?
Total content
= 402
Sucrose = 250
% sucrose=
250 x 100
402
= 62.19%

73. A23 The mechanism
At source
• sucrose loaded into
phloem.
• Lowers water potential
• Water enters(by
osmosis, down………
gradient)
• Increases hydrostatic
pressure.
• Contents of tube flow to
sink.
At sink
• sucrose unloaded from
phloem.
• Lowers water potential
in sink
• Water leaves
• Reduces hydrostatic
pressure.

75. Model to explain pressure-flow

77. Quiz
• file:///Volumes/Campbell
%20Biology/medialib/assets/interactivemedia
/quizredirects/H36quiz.html
• Another animation
• http://academic.kellogg.edu/herbrandsonc/bi
o111/animations/0032.swf

78. Quiz
•file:///Volumes/Campbell
%20Biology/medialib/assets/interactivemedia/q
uizredirects/H36quiz.html