1. Transpiration and pressure flow
Water and Nutrients
Transpiration and pressure flow

2. 32.3 Transpiration pulls water up xylem vessels
Transpiration-cohesion-tension mechanism
Water’s cohesion describes its ability to stick to itself
Water’s adhesion describes its ability to stick to other surfaces; water adheres to the inner surface of xylem cells
(Think of sucking soft drink up a straw)
For the BioFlix Animation Transpiration, go to Animating and Video Files.
Teaching Tips
1. The cohesive property of water allows some insects to walk or stand on a liquid water surface. The cohesion and adhesion of water is also the reason why we need to dry ourselves off after taking a shower, since water still clings to our skin and hair.
2. Demonstrate or ask students to recall what happens when a soda straw is lifted out of a beverage: some of the beverage still sticks to the straw. This is an example of adhesion.
Copyright © 2009 Pearson Education, Inc.

3. Cohesion and adhesion in the xylem
Xylem sap
Mesophyll cells
Air space within leaf
Stoma 1
Outside air
Adhesion
Transpiration 4
Cell
wall
Water
molecule
Flow of water 2
Cohesion
by hydrogen
bonding
Xylem
cells
Cohesion and
adhesion in the xylem
Figure 32.3 The flow of water up a tree. 3
Root hair
Soil particle
Water
Water uptake from soil

4. 32.4 Guard cells control transpiration
open pores in leaves called stomata to allow CO2 to enter for photosynthesis
Water evaporates from the surface of leaves through stomata
Guard cells can regulate the amount of water lost from leaves by changing shape and closing the stomatal pore
Teaching Tips
1. The change in shape of guard cells is due to internal fluid pressure, or turgor—important in many other organisms. Turgor helps maintain the shape of plant cells, gives structure to the hydrostatic skeletons of sea anemones and earthworms, and causes a penis to become firm upon erection. Before addressing guard cells, you may challenge your class to explain what leaves, earthworms, and an erect penis have in common. The answer is turgor.
Copyright © 2009 Pearson Education, Inc.

5. H2O H2O H2O H2O H2O H2O K+ H2O H2O H2O H2O Stoma Guard cells Vacuole
Figure 32.4 How guard cells control stomata. K+
Vacuole
H2O
H2O
H2O
H2O
Stoma opening
Stoma closing

6. 32.4 Guard cells control transpiration
Regulation factors:
Open in the day, closed at night-triggered by sunlight
Low CO2 concentration signals open
Water availability
Teaching Tips
1. The change in shape of guard cells is due to internal fluid pressure, or turgor—important in many other organisms. Turgor helps maintain the shape of plant cells, gives structure to the hydrostatic skeletons of sea anemones and earthworms, and causes a penis to become firm upon erection. Before addressing guard cells, you may challenge your class to explain what leaves, earthworms, and an erect penis have in common. The answer is turgor.
Copyright © 2009 Pearson Education, Inc.

7. Phloem transports the products of photosynthesis throughout the plant
32.5
Phloem transports the products of photosynthesis throughout the plant
Phloem sap - sucrose and other solutes such as ions, amino acids, and hormones
Sugars are carried through phloem from sources to sinks
Student Misconceptions and Concerns
1. Although analogies are often useful, some of their particulars can be misleading. In many ways, the vascular tissues and movement of fluid through plants are unlike the circulatory system of vertebrates. Whereas vertebrates have a one-way flow of fluids propelled by a contracting heart through a contained tubular system, phloem sap, propelled instead by a pressure flow mechanism, can move in either direction.
Teaching Tips
1. Many phloem saps other than maple syrup are used commercially. For example, phloem sap from rubber trees native to the Brazilian Amazon was once the major source of rubber. (Most rubber is now synthetically produced.) Pine oil, derived from pine tree resin, is the active ingredient in Pine-Sol cleaner.
Copyright © 2009 Pearson Education, Inc.

8. 32.5 Phloem transports sugars
A sugar source
Leaves produce sugars via photosynthesis
Roots and other storage organs produce sugar via breakdown of starch
A sugar sink is a plant organ that is a net consumer of sugar or one that stores starch
Growing organs use sugar in cellular respiration
Roots and other organs store unused sugars as starch
Student Misconceptions and Concerns
1. Although analogies are often useful, some of their particulars can be misleading. In many ways, the vascular tissues and movement of fluid through plants are unlike the circulatory system of vertebrates. Whereas vertebrates have a one-way flow of fluids propelled by a contracting heart through a contained tubular system, phloem sap, propelled instead by a pressure flow mechanism, can move in either direction.
Teaching Tips
1. Many phloem saps other than maple syrup are used commercially. For example, phloem sap from rubber trees native to the Brazilian Amazon was once the major source of rubber. (Most rubber is now synthetically produced.) Pine oil, derived from pine tree resin, is the active ingredient in Pine-Sol cleaner.
Copyright © 2009 Pearson Education, Inc.

9. 32.5 Phloem transports sugars
The pressure flow mechanism
High solute concentration caused by the sugar in tubes causes water to rush in from nearby xylem cells
Flow of water into tubes increases pressure at sources
At sinks, sugars are unloaded from tubes and solute concentration decreases; water is lost and pressure is low
The pressure gradient drives rapid movement of sugars from sources to sinks
Student Misconceptions and Concerns
1. Although analogies are often useful, some of their particulars can be misleading. In many ways, the vascular tissues and movement of fluid through plants are unlike the circulatory system of vertebrates. Whereas vertebrates have a one-way flow of fluids propelled by a contracting heart through a contained tubular system, phloem sap, propelled instead by a pressure flow mechanism, can move in either direction.
Teaching Tips
1. Many phloem saps other than maple syrup are used commercially. For example, phloem sap from rubber trees native to the Brazilian Amazon was once the major source of rubber. (Most rubber is now synthetically produced.) Pine oil, derived from pine tree resin, is the active ingredient in Pine-Sol cleaner.
Copyright © 2009 Pearson Education, Inc.

10. High sugar concentration Phloem Xylem High water pressure Sugar Sugar1
High water pressure
Sugar
Sugar
source 2
Water
Source
cell
Sieve plate
Sugar
sink
Sink
cell
Figure 32.5B Pressure flow in plant phloem from a sugar source to a sugar sink (and the return of water to the source via xylem). 3
Sugar 4
Water
Low sugar
concentration
Low water pressure