3.4 Transport in Plants
and
3.5 Control Systems
Cycling of Matter in
Living Systems
http://www.youtube.com/watch?v=U4rzLhz4HHk
Cohesion and Adhesion
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The attraction of one water molecule to
another is cohesion
Cohesion is due to the polar nature of the
water molecule
Adhesion is the ability of water molecules to
attract other molecules
Adhesion is also due the polarity of water
molecules
Cohesion

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
Cohesion = water
molecules are
attracted to other
water molecules
Due to Hydrogen
Bonds – polarity of
water molecule
Could be broken by a
surfactant - soap
Adhesion

Water molecules
attracted to other
substances
–
Example glass
Tension or Transpiration Pull

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The evaporation of water through the
stomata during the process of transpiration
creased a tension or transpiration pull
As each molecule evaporates, it creates a
pull on the adjacent water molecules
Combine this with the forces of adhesion and
cohesion it draws water up the xylem to the
leaves
The Effect of Tonicity of Plant
Cells
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Tonicity is the concentration of solute
particles in a solution
In a hypertonic environment, the plant
appears wilted
In a hypotonic environment, water enters by
osmosis and the cells become turgid
Plant Control Systems
Response to Stimulus
Phototropism
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Photo – sunlight
Tropism – the movement of plant is response
to stimulus
–
Tropism can either be positive or negative

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Positive grows towards stimulus
Negative grows away from stimulus
The stem exhibits positive phototropism
The root exhibits a weak negative
phototropism
https://www.youtube.com/watch?v=zHe7y8cy-7Y
Gravitropism

Stems grow against the gravitational force
and so show negative gravitropism while
roots grow towards the gravitational force
and so show positive gravitropism
https://www.youtube.com/watch?v=mYZXax8V_L0
Other Mechanisms

Plants respond to other stimuli other than
light and gravity. These stimuli include:
–
–
–
–
–
Touch https://www.youtube.com/watch?v=TTyuisUCcvo
Temperature
Chemicals
Water
Etc
https://www.youtube.com/watch?v=MnY_cCRELvs
Homework:
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Tropism Concept Map
Check and Reflect p. 322 #1-5
Check and Reflect p. 328 # 1-3