TOPIC 9.2 – TRANSPORT IN PHLOEM
9.2 – A - Phloem
INTRO
IB BIO – 9.2 3
https://i.ytimg.com/vi/LQ03xIkLLQU/maxresdefault.jpg
As noted in 9.1, plants transport water and nutrients throughout
their body in vascular bundles. These bundles contain the xylem
and phloem tissues.
Skills
S1: Identification of xylem and phloem in microscope images of stem and root.
Key Terms
Xylem
Phloem
IB BIO – 9.2 4
http://media.gettyimages.com/photos/alfalfa-herbaceous-dicot-20x-shows-vascular-bundles-arranged-in-a-picture-id139803630
Xylem and phloem can be visualized using different types of
microscopy. Phloem are typically smaller than xylem and are
located towards the outside of bundles in stems and roots.
Skills
S1: Identification of xylem and phloem in microscope images of stem and root.
Key Terms
Xylem
Phloem
IB BIO – 9.2 5
http://plantphys.info/plant_physiology/images/stemvb.jpg
Xylem & Phloem Images
To the left is a light microscope
image of a stem cross section.
• Phloem are the small tubes
towards the top of the image.
• Xylem are the larger tubes
closer to the center of the
stem.
The xylem and phloem are
separated by the vascular
cambium
Skills
S1: Identification of xylem and phloem in microscope images of stem and root.
Key Terms
Xylem
Phloem
IB BIO – 9.2 6Xylem & Phloem Images
To the left is a scanning electron
micrograph of vascular bundle.
• Xylem are the large green
tubes to the right.
• Phloem are the small yellow
tubes on the left.
The xylem and phloem are
separated by the vascular
cambium shown in orange.
https://s-media-cache-ak0.pinimg.com/originals/d4/6f/5c/d46f5c9eee8c6e18497d4a9d60675381.jpg
Understandings
U1: Plants transport organic compounds from sources to sinks.
Phloem tissues are found throughout plant bodies and are
responsible for transporting organic compounds.
Phloem structures include:
Key Terms
Phloem
Sieve Tube Cells
IB BIO – 9.2 7
https://online.science.psu.edu/sites/default/files/biol011/Fig-9-12-Sieve-Tubes.jpg
• Columns of sieve tube cells,
separated by perforated walls
called sieve plates.
• Companion cells, which
provide ATP and nutrients for
cell functions.
Applications
A1: Structure–function relationships of phloem sieve tubes.
Key Terms
Phloem
Sieve Tube Cells
IB BIO – 9.2 8
https://upload.wikimedia.org/wikipedia/commons/thumb/2/29/Apoplast_and_symplast_pathways.svg/2000px-Apoplast_and_symplast_pathways.svg.png
The structure of phloem sieve tube cells is related to their function.
The cytoplasm of companion cells is connected with sieve tubes cell
via the plesmodesmata.
Sieve tube cell walls provide the rigidity necessary to increase
internal pressure. The perforation of sieve plates also reduces
resistance to sap flow through tube.
Understandings
U1: Plants transport organic compounds from sources to sinks.
Key Terms
Phloem
Source
Sink
IB BIO – 9.2 9
http://plantsinaction.science.uq.edu.au/edition1/files/Fig%205.20.png
Phloem components transport
organic solutes in a process called
translocation. Compounds are
transported from source to sink:
• Source – tissues with surplus
organic compounds
Ex. green leaves/stems, storage
tissues, tap roots, tubers, etc.
• Sink – tissues that consume and
need organic compounds
Ex. roots, developing fruits/seeds,
growing leaves
Understandings
U1: Plants transport organic compounds from sources to sinks.
Key Terms
Phloem
Source
Sink
IB BIO – 9.2 10
http://www.wineland.co.za/wp-content/uploads/2017/08/Sugars-on-move-through-vine-Figure-1_WEB.jpg
Sometimes, plant sinks can turn into sources and vice versa.
Because of this, the phloem must be able to transport compounds in
both directions. This is an active process and requires energy.
REVIE
WIB BIO – 9.2 111. State the function of phloem
2. Outline how to identify xylem and phloem in
images.
3. Describe how the structure sieve tube cells is
adapted to their function.
9.2 – B - Translocation
Understandings
Key Terms
Translocation
IB BIO – 9.2 13
http://biology-igcse.weebly.com/uploads/1/5/0/7/15070316/499195_orig.png
Translocation is the process in plants that transports organic
materials between tissues (sources to sinks). The overall movement
is the result of both active and passive processes.
Understandings
U3: Active transport is used to load organic compounds into phloem sieve tubes at the source.
Key Terms
Translocation
PhloemLoading
IB BIO – 9.2 14
http://classconnection.s3.amazonaws.com/193/flashcards/1242193/jpg/bulk_flow1330467690160.jpg
Sucrose is the most abundant sugar in phloem sap. Molecules are
transported from source cells into the phloem in an active process
called loading. This increases the concentration in companion cells.
Understandings
U4: High concentrations of solutes in phloem at the source lead to water uptake by osmosis.
Key Terms
Translocation
PhloemLoading
IB BIO – 9.2 15
http://classconnection.s3.amazonaws.com/193/flashcards/1242193/jpg/bulk_flow1330467690160.jpg
Sucrose molecules then diffuse down the concentration gradient into
the phloem sieve tube. A high concentration of sugar results in the
movement of water from the xylem into the phloem via osmosis.
Understandings
U2: Incompressibility of water allows transport along hydrostatic pressure gradients.
Key Terms
Translocation
IB BIO – 9.2 16
https://classconnection.s3.amazonaws.com/558/flashcards/183558/png/picture91335365188079.png
Because of cell wall rigidity and the
incompressibility of water, the influx
of water increases hydrostatic
pressure within the phloem.
This pressure results in the movment
of sap throughout the plant.
Understandings
U5: Raised pressure causes the content of phloem to flow towards sinks.
Key Terms
Translocation
IB BIO – 9.2 17Differences in pressure results in
sap being transported away from
areas of high pressure (sourcea).
When contents reach a sink, sucrose
is absorbed and used or converted
to starch for storage.
The resulting decrease in solute
concentration reduces osmotic
pressure.
http://classconnection.s3.amazonaws.com/193/flashcards/1242193/jpg/bulk_flow1330467690160.jpg
Understandings
U5: Raised pressure causes the content of phloem to flow towards sinks.
Key Terms
Translocation
IB BIO – 9.2 18This movement of organic
compounds is collectively
referred to as the
pressure-flow hypothesis.
For more information,
follow the link below:
• McGraw-Hill Animation
http://classconnection.s3.amazonaws.com/193/flashcards/1242193/jpg/bulk_flow1330467690160.jpg
Skills
S2: Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-labeled carbon dioxide.
Key Terms
IB BIO – 9.2 19
http://bio1152.nicerweb.com/Locked/media/ch36/36_19PhloemSapFlow.jpg
Compared with other plant products, phloem sap is very nutrient-
rich. Aphids are insects that use mouth stylets to penetrate plant
tissues to reach the sap.
Skills
S2: Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-labeled carbon dioxide.
Key Terms
IB BIO – 9.2 20
http://bio1152.nicerweb.com/Locked/media/ch36/36_19PhloemSapFlow.jpg
Radioactive CO2 and aphids can be used to detect transport rates in
plants. After being exposed for short periods, plants uptake the CO2
and synthesize sucrose which is then transported.
Aphids colonies are placed at measured distances along the stem.
Then, the amount of radioactive CO2 that has been taken up is
measured.
REVIE
WIB BIO – 9.2 211. Discuss the translocation of sugars in plants.
Include the following key terms in your discussion.
- Xylem / Phloem
- Active transport
- Sucrose
- Hydrostatic pressure
- Osmosis
- Loading
- Source / Sink
- Sap
VID
EO
SIB BIO – 9.2 22• Fuse School: Translocation
https://www.youtube.com/watch?v=QXdujo4PZ7c
• Aphid Stylectomy to Get Pure Phloem Saphttps://www.youtube.com/watch?v=i6OVYj9Ia2Y