activity of water plant physiology uni spring 2006
TRANSCRIPT
Activity of Water
Plant Physiology UNI
Spring 2006
Overview
• Physical activity of water– Effect of temperature– Effect of pressure
• Chemical activity of water– Includes physical effects (T, P)– Also other effects
• Combining to get water potential
Physical activity of water
• Molecules have energy
• Molecules move around
air
water
Temperature effect
• Absolute zero
• Cold
• Medium
• Hot
Absolute Zero
air
water
NO MOVEMENT
Cold Temperature
air
water
SLOW MOVEMENT
Medium Temperature
air
water
MEDIUM MOVEMENT
Hot Temperature
air
water
FAST MOVEMENT
Effect of Pressure
• Low pressure
• Medium pressure
• High pressure
PPP
Low Pressure
air
water
SLOW MOVEMENT
P
Medium Pressure
air
water
MEDIUM MOVEMENT
P
High Pressure
air
water
FAST MOVEMENT
P
To increase or decrease activity
• Increase or decrease pressure
• Increase or decrease temperature
Chemical activity of molecules
• Based on physical environment (T, P)
• Also based on chemical environment– Determines what a molecule interacts with– Determines the effect of the interactions
Physical and chemical effects
• Molecules have physical activity
• Also chemical activity– Interact with other chemicals – Each molecule behaves in its own way
• Water acts like water• Ca acts like Ca
– What affects the chemical activity?– How much?
Without solutes
air
water
WATER MOLECULE NOT TIED DOWN BY SOLUTES
STANDARD WATER ACTIVITY
++ +
+
__
_
Add solutes
air
water
SLOWER MOVEMENT
WATER MOLECULE PARTLY COVERED
WATER ACTIVITY IS LOWER
Change Water Activity
• Increase– ↑ temperature– ↑ pressure
• Decrease– ↓ temperature– ↓ pressure– add solutes
• More solutes = more effect
Pure Water, Standard T, P
air
water
WATER ACTIVITY OF PURE WATER = STANDARD
STANDARD = 0
THIS WATER ACTIVITY = 0
COMPARE ALL WATER TO THIS STANDARD
Water Potential
• Water activity of your solution compared to water activity of standard solution
• Standard solution = 0
• Your solution can be – Same activity (WP = 0)– Lower activity (WP < 0)– Higher activity (WP > 0)
• Doesn’t occur in biology
Need to get some numbers
• Water potential scale
• Like temperature scale
Absolute & Relative Scales: Temperature
Relative Scales: Water Potential
Water potential scale
• The water in a cell (beaker, bucket, trunk)– Not the other chemicals
• Distributed characteristic (all the same)– Like temperature
• Compared to standard (0)
• Can be positive, zero or negative
• Expresses effect of P, T, solutes– On water, compared to standard
Summary
• Physical activity of water molecules changes with– Temperature, pressure
• Chemical activity of water molecules changes with solutes
• Water potential tells us the total activity– Compared to pure water, standard TP
• WP can be +, 0, -