Chapter 9: Water and Transport in Plants Flashcards
Osmosis & Turgor pressure
If there is water outside it will be hypertonic inside.
High turgor pressure is the pressure of water against the cell wall and stiffing the wall. Or high water potential.
If they are placed in a hypertonic solution the water will flow out of the cell.
Plasmolysis
When the cell shrinks away from the wall when water flows out.
Imbition
Cells attract water by their electric charge
Active Transport
- There is no active transport for water
- Occurs at the cell membranes, requires ATP
- There is a gradient that is positive on the outside and negative on the inside.
- Co-Transport mechanism that allows the hydrogen to come in as long as it is with a nitrate.
Protons - Direct - Cations* - Potential
How do plants live in salty environments?
They have a trick that allows them to avoid plasmolysis.
They fill their tissues with other things that blocks a lot of sodium to come in.
Examples: Mangroves, pickle weed, Saltbush
Salicorina (Pickleweed)
They can dump excess salt off of their tips
Evaportransportation
- It is the main route that water moves through a plant.
- the water comes in through the root hairs, passes through the endodermis and into the xylem
- Keeps cell supplied
- Raw material for photosynthesis
- Capture CO2
- Cooling plant
- The average birch tree uses 2,000 gallons of water per day
- Olive trees use up to 50 gallons of water per day
Water process moves water up through the plant
- passive process that uses almost no metabolic energy.
- 10x better than a “perfect pump”
- Takes place mostly in dead cells.
How it works: (ideas)
-capillary action - water is charged (like the meniscus on glass). Only works up to one meter
- Pericycle cells causes active transport by root pressure. root pressure would work only one meter.
Cohesion Tention theory
- Relies on strong cohesion of water
- Starts at the top of the plant with cells full of water.
- The curvature of the meniscus causes a suction and tention of more water using cohesion
- Water potential in mesophyll drops
- Water drawn from yxylem in leaf vein
- Water pulled up molecule by molecule through xylem
- see slide
Evidence of Cohesion-Tension Theory
- Transpiration best at low humidity open stomata
- Negative Pressure in xylem (sucking)
- Plant stems contract during transpiration (Shrink)
- Cavitation “pops” in xylem during transpiration
Problems with the Cohesion Tension Model
- Water is not as cohesive as is needed
- Requires extreme negative pressures in the xylem
- Cavitation should cause irreversible embolism
- Many trees function near the cavitation limit.
Compensating Pressure Model (Alternative to Cohesion Tension)
- Living phloem & rays near xylem have positive pressure
- Root pressure + evaporation work as in other models.
- Live cells provide static pressure to xylem
- After cavitation water from live cells repair embolism
Evidence of the Compensating Pressure model
- Flash - freezing shows many embolized tracheids/ vessels
- Embolism highest in morning, repairs in afternoon
- Sugars are in phloem, starches to sugars in rays
- Micrographs show water oozing into xylem
Regulation of the rate of transportation
- High humidity slows it down.
- Temperature
- Opening and closing of the stomata
- Bordered pits in vessels
Opening and closing the stomata
- Presence of light
— Most plants: Diurnal opening
— CAM photosynthesis: nocturnal opening. - Presence of water
- Anatomical featured of leaves & stomata
– Stomata in crypts
– Epidermal hairs
