Transport In Plants – C3.4
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How can such a large
tree transport water from
the ground up into its top
branches?
Without water the tree
will die because water is
a reactant in
photosynthesis.
We might guess it costs
the tree a lot of energy!
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We have already learned about a
handful of processes which move water
in a plant.
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Osmosis
Diffusion
Active Transport
Transpiration
We can now put all the pieces together
to get a clearer picture of material
movement in plants.
Cohesion and Adhesion
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Plants act as pumps to pump water from the roots to
the leaves. Water has certain properties which help
plants use water efficiently.
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Water molecules are attracted to each other - Cohesion
Water is a polar molecule where a tiny positive charge is
attracted to a tiny negative charge on another water molecule.
Cohesion and Adhesion
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Since water is polar, it attracts itself to molecules of
other substances.
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Water molecules “stick” to other substances. This called Adhesion.
In a plant the water molecules would adhere to the walls of the
xylem.
Root Pressure
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Plants actively transport minerals into the root cells.
As a result, the root becomes hypertonic to its
surroundings and water follows. The water moving
into the roots creates root pressure.
This can be tested by cutting a plant and seeing the
water seep up into the cut of the stem
Transpiration Pull
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The evaporation of water through stomata and
lenticels creates a tension or transpiration pull.
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This pull is primarily responsible for bringing water
from the xylem into the ground tissue.
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Transpiration depends on temperature - high temps
increase transpiration
Tonicity in Plants
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What happens when you put a plant cell in salt
water?
The effect is called plasmolysis. This is where the
cell membrane is no longer pushing against the cell
wall.
Movement of Sugar in Plants
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Sugar is produced in the leaves - the source
Sugar must move in the plant to a place where it will
be used or stored - the sink
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Draw the figure on page 321 and label
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The movement of materials in and out of the phloem
is called the pressure-flow theory
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Control Systems - C3.5
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You can respond to the environment. When you
smell a pizza and you are hungry - you follow your
nose and chow down!
What about plants? Can they respond to their
environment?
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How do they know they know what direction their roots
should go?
How do plants grow up toward the light?
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As humans, we can respond to stimuli in our
environment.
A stimuli is a change in the environment
which creates a response within an organism.
Phototropism
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Plants need to carry out photosynthesis to survive. In
order for plants to be successful, they must be
efficient at gathering the materials necessary for
photosynthesis.
Plants will grow toward the light - phototropism.
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Stems show positive phototropism because they follow
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light
Roots show negative phototropism because they grow away
from the light
Gravitropism
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Plants also respond to
another stimulus gravity.
Gravity effects plant
growth and is called
gravitropism.
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Stems show negative
gravitropism
Roots show positive
gravitropism
Plant Response to Stimuli
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Plants that have roots growing away from light and
that follow gravity are more likely to find minerals
and water.
Plants that have stems grow toward the light and
against gravity are more likely to receive the solar
energy needed for photosynthesis.
“Tropism's” are important control systems which
guide a plant reaction to certain stimuli.
Investigating Phototropism
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In 1880, Charles Darwin and his son Francis asked
the question: What part of the plant detects and
responds to the phototropic stimulus?
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They hypothesized that cells in the tip of a seedling
were communicating with cells in the stem that bent a
plant toward the light
They tested this with a simple experiment laid out on
page 327.
Investigating Phototropism
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In 1913, Peter Boysen-Jensen investigated how the tip
and the seedling communicated.
The area of the plant which bends toward the light was
called the area of elongation because the cells on the
“dark side” of the stem became longer causing the
bend.
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Boysen-Jensen snipped off the tip of the seedling and paint gelatin on
the end, then put the tip on - the seedling followed the light
He then snipped the tip and placed a piece of thin mineral called mica
in-between the tip and the seedling - no phototropism was observed
Peter Boysen-Jensen hypothesized that whatever was responsible for
communicating between the tip and the seedling must be able to
diffuse through gelatin but not mica.
Investigating Phototropism
Darwins Experiment
Investigating Phototropism
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In 1926, F.W. Went isolated the substance that was
responsible for communication of phototropism
responses.
The substance was called auxin, a hormone which is
produced in a plant and then transported to cells which
elongate upon its contact.
Mechanism of Gravitropism
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Scientist believe that
plants rely on heavy
starch particles as an
indicator of gravity
If a plant is knocked over
– the starch grains shift
and settle in a new
location
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After movement is
detected, then a growth
response results
Other Control Mechanisms
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Pea plants – Climb on a chain link fence
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Poinsettias – need longer nights to flower
(Christmas flower)
HOMEWORK
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Read pages 315 -328
Do worksheet C3.4- Transport in plants
Do worksheet C3.5 – Control Systems
Prepare for Section C3.0 Quiz
Do Section 3 Review – p.330
#2,3,7,9,10,12,14,16,17-20, 22,23,25
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Prepare for Biology Vocabulary Quiz
Homework
Prepare for Unit Exam
 Do Unit Review – p. 334-335
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#’s 2-5,7-11, 13-15, 17-25