EE BIOL 162 Lecture Notes - Lecture 1: Endodermis, Xylem, Casparian Strip
8 Jun 2018
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Lecture Notes – Week 3 Tuesday
The Soil-Plant Atmosphere Continuum
• The texture of the soil (particle diameter) – coarse, fine, silt, clay
• The spaces between the different particles differs with the diameter
• How do we get water out of soil?
o Water potential of the soil? Water will go from less negative to more negative
o Solute potetial of the soil is’t that iportat copared to the pressure
o Negative pressure potential as the soil dries out
▪ Comes from surface tension
• Vulnerability curve
• Soil hydraulic conductivity dries as soil dries
• Why is it difficult for plants to withdraw water from dry soil?
o Driving force is lower due to the negative pressure & hydraulic conductivity declines
• What is the type of water transport, driving force and transport coefficient?
o Bulk transport
• How does the driving force depend on the soil moisture?
o As soil dries, driving force declines
• How does the transport coefficient depend on the soil moisture?
Root Hairs
• Rate of water uptake by short segments at various positions
o Entire surface equally permeable
o Only zones near root tips permeable
o Tips water is taken up and growth occurs
• What is the role of the Casparian Strip in water uptake and ion uptake in the root?
o Prevents toxins from entering the xylem into the plant
• What is the name of the tissue involved?
o Endodermis tissue
• How does water cross this tissue? Why do plants invest in such a tissue?
• How does water move from the soil to the root xylem?
o Bulk flow and osmosis
• Only angiosperms have vessels
• Primary cell wall is formed first and is in the middle
• Tracheid or vessels
• Pit – there is no secondary cell walls
• Suppose that a pine tree has tracheids of 10microm diameter, and a sunflower has vessels of 50
microm diameter. Kh is higher for the sunflower by up to how many times?
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