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3.4 Transport in Plants
and
3.5 Control Systems
Cycling of Matter in
Living Systems
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
Tension or Transpiration Pull
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The evaporation of water through the
stomata during the process of transpiration
creates 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
Phototropism
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“photo” means light, and “tropism” means
movement
Stems exhibit positive phototropism, they
grow towards the light
Roots exhibit negative phototropism, they
grow away form the light
Gravitropism
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Stems grow against the gravitational force
and so show negative gravitropism while
roots grow towards the gravitational force
and so show positive gravitropism
Homework:
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WB pg 201-206 ALL