1. Topics 9.1 and 9.2: Transport in Plants

2. 9.1 Transport in the xylem of plants

3. Absorption of water into roots
Must happen before water can be transported up xylem
Active uptake of mineral ions in the roots causes absorption of water by osmosis.
detailed mechanism

4. Transpiration Transpiration: evaporation of water from leaves
Transpiration is the inevitable consequence of gas exchange in the leaf.
Why?

5. Transport of Xylem Sap (From roots to leaves)
Plants transport water from the roots to the leaves to replace losses from transpiration.
Transpiration
pulls water from roots (transpirational pull) due to cohesion of water
Adhesion
Prevents water falling due to gravity
This happens in Xylem.
Animations
Great video explaining why this is Amazing!
Root pressure: at night (low transpiration), root cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; guttation

6. Transpiration, Cohesion and Adhesion produce tension that pulls water up the stem
Sometimes called cohesion-tension theory
IB says it like this:
The cohesive property of water and the structure of the xylem vessels allow transport under tension.
The adhesive property of water and evaporation generate tension forces in leaf cell walls.

7. Xylem Structure and function
xylem: transports water and dissolved minerals (xylem sap) from roots to leaves
2 cell types: tracheids & vessel elements: elongated cells dead at maturity
Thick cell walls strengthened with lignin (a polymer)
Prevents collapse at low pressures
Like dead hollow straws!

8. Skill: Drawing the structure of primary xylem vessels in sections of stems based on microscope images.

9. Nature of Science: Use models as representations of the real world—mechanisms involved in water transport in the xylem can be investigated using apparatus and materials that show similarities in structure to plant tissues. (1.10)
Application: Models of water transport in xylem using simple apparatus including blotting of filter paper, porous pots and capillary tubing.

10. Skill: Measurement of transpiration rates using potometers
Skill: Measurement of transpiration rates using potometers. (Practical 7)
Skill: Design of an experiment to test hypotheses about the effect of temperature or humidity on transpiration rates.

11. Interesting Article on using xylem to purify water.
This is the short version online:
Short version in my Docs: ..\..\..\..\AP BIO\articles\Plants\Water Filtration Using Plant Xylem Summary.docx
Full Scientific Paper Online:
Full Scientific Paper in my docs: ..\..\..\..\AP BIO\articles\Plants\Water Filtration Using Plant Xylem Complete Scientific Paper.pdf

12. Factors that influence transpiration
Light  more light = higher rate in most plants
Temperature  higher temp=higher rate
Wind  more wind = higher rate
Humidity  higher humidity= lower rate
Guard cells control the size of the stomata
By opening and closing the stomata
abscisic acid (a hormone) closes stomata

13. Application: Adaptations of plants in deserts and in saline soils for water conservation.

14. Xerophyte adaptations
Xerophytes (plants adapted to arid environments)~
thick waxy cuticle
Deep roots
Stomata in pits surrounded by hairs
Water storage tissue
Low growth form
CAM physiology (Stomata open at night)
Reduced or rolled leaves (to reduce SA)
Ex. small spines for leaves

15. Halophyte Adaptations
Halophytes (plants adapted to saline environments)~
thick waxy cuticle
Deep roots
Sunken stomata
Water storage tissue
Low growth form
Reduced or rolled leaves (to reduce SA)
Ex. small spines for leaves
Structures for removing salt build-up
Mangroves

16. Interesting article on using halophytes to make biofuel:

17. 9.2 Translocation of Phloem Sap
Active Translocation: transport of organic molecules (sugars and amino acids) by phloem from sources to sinks
Sugar source: sugar production organ (mature leaves)
Sugar sink: sugar storage organ (growing roots, tips, stems, fruit)

18. Translocation of Phloem Sap (continued)
How?
Active transport is used to load organic compounds into phloem sieve tubes at the source
This causes water uptake by osmosis
This raises hydrostatic pressure that forces sap to flow along tube towards sinks
The unloading of organic molecules at sinks results in loss of water from phloem at the sink (produces lower pressure near sink)
xylem then recycles water from sink to source
IMPORTANT NOTE: sap MAY MOVE UP OR DOWN!! (depending on pressure)

19. IB Note:
Incompressibility of water allows transport along hydrostatic pressure gradients.

20. Application: Structure–function relationships of phloem sieve tubes.
Phloem sieve tubes are made of columns of sieve tube cells
Living
Rigid cell walls
Connected by sieve plates (perforated cell walls)
Reduced cytoplasm
No nucleus
Closely associated with companion cells that perform many of the genetic and metabolic functions for them– (connected by wide plasmodesmata to companion cells)
For each structural aspect, explain how it relates to the function of sieve tubes.

21. Skill: Identification of xylem and phloem in microscope images of stem and root.
See p. 420 and 421, examine the images and write down several key ways to identify xylem and phloem here in your notes

22. Skill: Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-labelled carbon dioxide.
HW tonight– see p. 417 and explain this technique here in your notes

23. Homework from book
P. 418 and 419 Data-based questions Answer all questions clearly on this Google doc:

24. Nature of science:
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. (1.8)

25. Whole Plant Transport overview
1- Roots take in minerals from soil by active transport. Water follows by osmosis.
2- Transpiration, the loss of water from leaves, creates a force that pulls xylem sap upwards
3- Water and minerals are transported upward from roots to shoots as xylem sap
4- Leaves exchange CO2 and O2 through stomata
5- Sugar is produced by photosynthesis in leaves
6- Sugar is transported as phloem sap to roots and other parts of plant
7- Roots exchange gases with air spaces of soil (supports cellular respiration in roots)

26. End of IB Stuff

27. From Soil to Roots
Mineral ions in soil (potassium, phosphate, nitrates etc.)
Traveling through the soil to the root
Diffusion
Fungal hyphae- the minerals travel through the fungus to the root (mutualism)
Mass flow of water in the soil carrying ions
Absorption into the root
Active transport (why?)
Water follows passively by osmosis.

28. Transport Overview
1- uptake and loss of water and solutes by individual cells (root cells)
2- short-distance transport from cell to cell (sugar loading from leaves to phloem)
3- long-distance transport of sap within xylem and phloem in whole plant

29. Cellular Transport
Water transport √ Osmosis; hyper-; hypo-; iso- tonic
Water Potential = combined effect of solute concentration and pressure created by cell wall
Ψ = Ψp + Ψs
Ψ = 0 is pure water at 1 atm pressure
Water moves from high to low water potential
More solute = lower water potential
More pressure = higher water potential
Flaccid (limp, isotonic);
Plasmolysis (cell loses water in a hypertonic environment; plasma membrane pulls away);
Turgor pressure (influx of water due to osmosis; hypotonic environment)

30. Transport within tissues/organs
Tonoplast vacuole membrane
Plasmodesmata (components) cytosolic connection
Symplast route (lateral) cytoplasmic continuum
Apoplast route (lateral) continuum of cell walls
Bulk flow (long distance) movement of a fluid by pressure (xylem)