Transcript Transport in Plants - Mr Dolan`s Science Page

Transport in Plants
a) Xylem
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Dead, hollow cells stacked on top of one another
forming a hollow tube.
Conducts water and minerals from roots of plants to
stem and leaves.
Transport in Xylem
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Water moves into the plant by osmosis through the root
hairs into the epidermal cells.
Water is then transported from the root up the plant
stem through the xylem: water and minerals move by
diffusion into tissues of the plant.
How does water move against the
force of gravity?
1.
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Root Pressure
Pressure exerted on
root when soil
moisture is high
2. Capillary Action
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The tendency of a liquid
to rise in narrow tubes
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result of the
intermolecular attraction
within the liquid
3. Cohesion Tension
Theory
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Water is a polar molecule (bond
electrons pulled closer to oxygen)
When water molecules approach
they are attracted to each other and
form a Hydrogen Bond.
Water is constantly lost by
transpiration in the leaf through the
stoma.
When one water molecule is lost
another is pulled along by the
cohesive force of waters hydrogen
bonds.
Terminology
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Adhesion: Attractive
force between unlike
molecules
Water may cling to other
groups of molecules
such as cellulose
Water clings to walls of
xylem helping it to move
upward against gravity
Terminology Continued
Cohesion: Attractive force
between like molecules
 Water is polar which means
one end of the water
molecule is attracted to the
other end of a different
molecule thus the molecules
stick together.
 Water molecules use
cohesion to tug each other
from root to leaf.
How is transpiration controlled?
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Controlled by opening
and closing of
stomates
Guard cells control the
movement of stomates
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Turgid (water filled) 
forces cells to open
Flaccid (water lost) 
forces cells to close
What about minerals?
- Minerals move by Active
Transport in the form of
mineral ions from the soil
into the roots; these ions
are incorporated into
various compounds and
then released into the
xylem where they move
with water.
Lets Review Cohesion Theory
 1.
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Transpiration
Water evaporates through the stomata of the leaves
2. Result
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Tension which provides the force needed for the
water to move up the xylem, against gravity.
3. Cohesion:
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Within the xylem, hydrogen bonds hold nearby
water molecules together firmly, like a chain
(strongly attracted)
4. Cohesion:
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Water molecules exiting the xylem in the leaf, tug on
the rest of the chain which is pulled up the xylem.
5. Adhesion
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Between water molecules and the xylem wall,
aids in the ability of the water column to move
upward (cling to wall of xylem due to attraction)
Water enters the root hairs by osmosis to
replace, water which has been pulled by the
xylem.
b) Phloem
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Living cells containing cytoplasm that allow exchange
of materials with the surrounding cells.
Transports organic materials such as nutrients and
hormones throughout the plant.
Transport of Carbohydrates in
Phloem
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Experiments with radioactive isotopes have
shown that carbohydrates travel in the phloem
Carbohydrates (glucose, sucrose, starch) are
produced in the leaves (source)
The stem, root tip, flowers and fruits need carbs
for growth (sink)
Movement of carbohydrates from source to sink
is called translocation
Translocation
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Cells of the phloem
form a continuous
pipeline called a sieve
tube.
Sieve tube cells are
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perforated at the end
living cells that have lost
their nuclei
Companion cells
therefore take over
control of sieve cells
activities
Pressure Flow Model
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Most accepted theory for
translocation
Result of differences in
pressure
Main Points of Model
1.
2.
3.
4.
5.
Active transport moves sugar molecules from source
into sieve tube
Solution inside tube is hypertonic  water enters
tubes by osmosis from neighbouring cells of xylem
 increases hydrostatic pressure inside sieve tubes
Increased pressure pushes sap down into next sieve
tube…and so on
Active transport moves sugar from sieve tubes into
sink cells moving water with it by osmosis
This relieves pressure in tube and leaves sieve cells
hypotonic
Continued
6. Difference in pressure moves sap from source
to sink
7. Sugar in sink cells is stored as starch or used for
metabolism
8. Xylem recycles water from sink to source
Videos
http://www.biol.unizh.ch/filme/life_on_earth/
Chapter_24/Present/Activities/24_4/24_4_1a.s
wf
• http://nortonbooks.com/college/biology/anim
ations/ch31a06.swf
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Homework
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Read pages 320-321
Answer questions page 326 #1-7