Activity of Water

1
Activity of Water

• Plant Physiology UNI
• Spring 2006

2
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

3
Physical activity of water
air

• Molecules have energy
• Molecules move around

water
4
Temperature effect

• Hot

• Medium

• Cold

• Absolute zero

5
Absolute Zero
NO MOVEMENT
6
Cold Temperature
air
water
SLOW MOVEMENT
7
Medium Temperature
air
water
MEDIUM MOVEMENT
8
Hot Temperature
air
water
FAST MOVEMENT
9
Effect of Pressure

• High pressure

• Low pressure

• Medium pressure

10
Low Pressure
air
water
P
SLOW MOVEMENT
11
Medium Pressure
air
water
P
MEDIUM MOVEMENT
12
High Pressure
air
water
P
FAST MOVEMENT
13
To increase or decrease activity

• Increase or decrease pressure
• Increase or decrease temperature

14
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

15
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?

16
Without solutes
air
water
WATER MOLECULE NOT TIED DOWN BY SOLUTES
STANDARD WATER ACTIVITY
17
Add solutes
air
SLOWER MOVEMENT
water
WATER MOLECULE PARTLY COVERED
WATER ACTIVITY IS LOWER
18
To decrease water activity

• Decrease temperature or pressure
• AndTie the water up chemically
• Add solutes
• Water partly busy with solutes
• Not fully free to act like water
• Lower chemical activity

19
Change Water Activity

• Increase
• ? temperature
• ? pressure
• Decrease
• ? temperature
• ? pressure
• add solutes
• More solutes more effect

20
Pure Water, Standard T, P
air
COMPARE ALL WATER TO THIS STANDARD
water
STANDARD 0
THIS WATER ACTIVITY 0
WATER ACTIVITY OF PURE WATER STANDARD
21
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 lt 0)
• Higher activity (WP gt 0)
• Doesnt occur in biology

22
Need to get some numbers

• Water potential scale
• Like temperature scale

23
Absolute Relative Scales Temperature
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Relative Scales Water Potential
25
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

26
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, -