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Lecture 20

Biology 2601A/B Lecture Notes - Lecture 20: Boundary Layer, Root Pressure, Wind Speed

Course Code
BIOL 2601A/B
Brent Sinclair

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Organismal Lecture 20
Water and Ion Balance in Plants
Plants Need Water
For biochemical reactions
To maintain structure (turgor pressure)
For photosynthesis
Boundary Layer
The boundary layer is the layer of unstirred air on the outside of the leaf; it provides
resistance to the water vapour molecules as they pass through it
The boundary layer has a higher vapour content, meaning that it isn’t as dry as the
Due to this, less water is lost from the leaf tissues when the stomata is open
The Boundary Layer is Disturbed by Wind
The higher the wind speed is, the
smaller the boundary layer will be, and
subsequently the length of the
diffusion path decreases
Therefore, more wind = more
Wind speed also tends to cool the
leaves and may cause sufficient
dryness to close the stomata; therefore
this occurs at extremely high wind
Boundary layers are also thicker over larger leaves (as seen in diagram)
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How Does Water Get Into the Plant?
Through the roots
Roots aren’t just a single structure; roots provide a lot of surface area
Roots will interact with water particles in-between the soil particles
Roots will absorb and transport upward to the stem virtually all water and minerals taken
up by plants
The root cap is not very
permeable; therefore water
will not be exchanged at
the top
The root hair zone is
where water and nutrients
will be transported into the
Root Hairs
Root hairs enhance water uptake by their ability to
penetrate water-containing capillary spaces
between soil particles
Increase several fold the volume of water
extracted from the soil
Extend between the film grains into films of water
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