Here are the key steps in phloem transport of sugars: 1. Sugars are actively loaded into the sieve tube elements in source tissues like leaves through plasma membrane transporters, using energy from ATP. 2. The sugars create an osmotic gradient that pulls water into the sieve tube elements through osmosis. This increases the hydrostatic pressure. 3. The pressure gradient drives bulk flow of sugars and water through the sieve tube elements to sink tissues like roots and fruits. 4. Companion cells provide energy to the sieve tube elements through plasmodesmata to power the transporters loading sugars against the concentration gradient. So in summary, phloem transport uses active transport of sugars into sieve

1. Announcements
• handouts for ch. 1 and 2 posted on ecommons
• This week’s sections meet in the greenhouse
Assignments:
• All labs need to be turned in by 2:00 on Friday
• First plant of the week is due at the beginning
of class on May 17th
• Also Quiz #4 is on Thursday

2. Leaf anatomy correction
Cuticle:
• Waxy layer covering the epidermis
• Impermeable to water
Cuticle and Epidermis inhibit water loss but also
inhibit CO2 diffusion

3. Fig. 34.11

4. A summary primary and secondary growth in a
woody stem

5. Primary growth
• Buds protect the apical
meristem
• Only buds consist of
primary tissues
• Lengthening of shoots/
roots and production of new
roots/shoots through
branching
Fig. 34.16

6. Secondary Woody Growth: Eudicots
Does not occur in monocots!!!
• Apical Meristem->
2 Lateral meristems
Vascular Cambium
Cork Cambium
Gymnosperms
Woody Eudicots
Fig 34.16

7. Secondary Woody Growth: Eudicots
Vascular Cambium
• 2ndary Xylem = wood;
water transport
• 2ndary Phloem= Bark;
photosynthate transport

8. Secondary Woody Growth
Bark
• Periderm
• Cork
• Cork Cambium
• Secondary Phloem

9. Secondary Woody Growth
Secondary Phloem
• Transport of photosynthates
from leaves to roots
Cork Cambium
• Tissue layer that produce Cork
Cork
• Outer waxy walled protective
cells

10. Girding blocks phloem transport

11. Secondary Woody Growth
Pith rays:
• Produce continuos
cylinder of vascular
cambium

12. Secondary Woody Growth
Products of Vascular Cambium
• 2ndary Xylem
• Vessel slements
• tracheids
• Supportive Fibers
• 2ndary Phloem
• Sieve tube elements
• Companion cells
• Fibers
• Parenchyma Cells

13. Secondary Woody Growth
Lenticels:
• Structures on stems that allow for gas
exchange
* for metabolic: allow CO2 to go out of cell

14. Shoot System
Consist of leaves,
stems, and flowers
Stems and Branches
• Support leaves
• Allow transport of
materials between
roots and leaves

15. Shoot System
Phytomer
• 1 or more leaves
attached at the node; an
internode, and 1 or more
axillary buds
Axillary Bud
• If active develops into
a new branch

16. Shoot System
Leaf
• Consist of a blade and a petiole.
• Petiole attaches leaves to
stems
Node: Point of leaf attached

17. Phyllotaxy (Leaf Arrangement):
How many leaves are attached at the node?
alternate
1 leaf per node
opposite
2 leaves per node
Whorled
3+ leaves per node

18. Root System
• Eudicots
- Tap root
• Often functions as carbohydrates storage organ
•Ex. Carrots, Sugar Beet
- Later roots:
• Roots that extend outward form the tap root

19. Root System
• Monocots
- Tap root
• Short lived
- Adventitious Roots
• Arise from the stem at ground level or below
• Form fibrous root system
- Prop Roots
• Help Support the shoot

20. Roots: Overall Function
• Anchorage and support of stems
• Carbohydrate storage
•Water and nutrient uptake

21. Biology 20B
CHAPTER 35
Water and Solute Transport

22. Transport in Plants
3 important modes of transport in plants
• Passive transport
• Diffusion of molecules across a membrane from a high to low
concentration gradient
- Ex. Osmosis
• Active transport
- The use of energy in the form of ATP to move ions against their
concentration gradient.
- Ex. Proton pump
• Facilitated trasnport
- Changes in the electron gradient within cells allows for diffusion
of ions via specific membrane channels
- Ex. K + movement

23. WATER AND SUGAR TRANSPORT
First, need to understand the passive movement of water:
• Water potential - tendency of water to move
across a membrane = ψ
• Osmosis- Passive diffusion of water from a
region with higher ψ to one of lower (more
negative) ψ
ψ = ψs + ψp
Water pot. = solute pot.+ pressure pot.
Generate osmotic pressure Physical pressure water is under

24. WATER AND SUGAR POTENTIAL
Osmosis = Passive diffusion of water from a
region with higher ψ to one of lower (more
negative) ψ .
ψs= usually negative
ψp= usually positive
Water always moves across a selectively
permeable membrane towards the region of
lower (more negative) water potential

25. Water Potential and Water Transport

26. ψs of a salt solution is LOWER than ψs of distilled water.
ψs of 0.1M solution = -0.23 Mpa
Mpa = “megapascals” atmospheric pressure = 0.1 Mpa
ψs of distilled water = 0.00 Mpa

27. Ex. Leeches
Salt on leeches changes the osmotic potential.
water leaves their bodies and they fall off

28. In an animal cell, “kerplow” it bursts
But in a plant cell.....
when higher ψ surround-> Turgor pressure~ 0.7 Mpa
Wall pressure = turgor pressure
“Turgid cell”

29. Turgor Pressure
• Turgor Pressure- pressure that is exerted
against the cell wall as a result of water
entering the cell

30. Plasmolysis
When lower ψ surrounds
(e.g. concentrated solution or dry air)
PLASMOLYSIS
= cells are “flaccid”
(=BAD)--> dehydration

31. Water in Plants
• Wilting and Rehydration (turgor pressure)
PLANT VIDEO PLACE HERE*

32. How does water move through the plants
Short -distance movement (within tissues)
(e.g. outer roots cells---> inner cells)
1. APOPLASTIC
• Between cells and cell walls
2. SYMPLASTIC
• Through cells (cytoplasm), cell to cell

34. Casparian strip
• Within endodermis
The Casparian strip prevents water and • Surrounds plumbing
ions in the apoplast from passing between
the endodermal cells into the stele. • Stops apoplastic flow
an
• Solutes & water can
ess
ast.
Endodermis
only enter through cell
membrane
Pericycle • Sophisticated pumps
Toxics out
Selective ion uptake
Casparian
• Pericycle

35. Transpiration
Leaves can loose up to 100% of their water in 1
hour
Plants retain less than 1% of the water they
absorb
no need to copy this*

36. Water is a Strange Molecule
• Polar molecule
• Adhesion - Sticks to other molecule
• Cohesion - water sticks to itself

37. Water Potential
• Differences in water Low water potential
potential determines Atmosphere ψ: -95.2 MPa
the direction that (Changes with humidityl
water moves usually very low)
Leaf ψ: -0.8 MPa
• Water always flows
(Depends on transpiration
from high to low water ratel low when stomata are
potential open_
• Water potential Root ψ: -0.6 MPa
gradient exist between (Medium -high)
the soil, plants, and the
atmosphere

38. How does water move through the plant?
Now we are in the leaves.
What generates the force that pulls the
water column through the shoot?
• The plants needs carbon
• The plant need to stay hydrated.
(A plant may lose 300 g of water
for every 1g of glucose produced)

39. How do stomata regulate water loss?
• 2 guard cells.
Flaccid: stoma closed
Turgid: stoma open
• Day: open & night: closed
Mechanism?
• Blue right receptor --->
• Stimulates proton pump...

40. How guard cells work: the proton pump (review)
1. H+ moves out against
elctronchem grandient
Use ATP energy
2. K+ and CL- moves in through
ion channel in response to -ψ
3. Water moves in by osmosis
because [ion] is high

41. Stomata close when:
Dark
High CO2
Water stress
High temp

42. Sugars: Translocation
• How do sugars made in leaves end up in other
parts of the plant?

43. Sugars are transported in the phloem
Aphid and Ants

44. Now, on to movement of sugars..
Translocation = phloem transport
• Energetically demanding process.
Sieve tube members (+companion cells)
+ Minerals, amino acids, hormones....
Materials can go either up or down
SOURCE vs. SINK
(but only one direction per tube)