Water Movement

1
Water Movement

• UNI Plant Physiology
• Spring 2005

2
Three Rules

• WP PP SP
• Membrane?
• Yes?Osmosis happens WP determines flow
• No?... Bulk flow happens PP determines flow
• Water flows from high to low

3
Ask yourself

• Is there a membrane?
• Choose WP or PP
• What are the WPs or PPs?
• Which one is lower?

4
Write it down, Say it out loud

• Write down the arithmetic
• Draw the arrow showing flow
• Explain it in words
• Helps you understand and remember
• Prepares you for tests

5
Now do the problem setDont go any further in
this presentation until you have done everything
you can on your own.Reading about solving
problems is like readingabout swimming. You will
drown if you read, then jump in the deep end of
the pool.
6
Done the problem set yet?OK, time to check the
thinking and the answers.Read and answer the
questions beforeclicking to continue.Watch
carefully something happens with each
click.Page Up to go back see it again.
7
Two limp, wilting leaf cells

• Is there a membrane here?
• Yes (one for each cell)
• Water potential is what counts
• Calculate water potentials
• SP PP WP
• Write them in as you go
• -4 0 ?
• -4
• -2 0 ?
• -2

-4
-2

• Which water potential is lower?
• -4 is lower than -2 (like temperature)

Draw arrow to show water flow.
8
Two ordinary (stiff) leaf cells

• Is there a membrane here?
• Yes (one for each cell)
• Water potential is what counts
• Calculate water potentials
• SP PP WP
• Write them in as you go
• -6 4 ?
• -2
• -4 3 ?
• -1

-2
-1

• Which water potential is lower?
• -2 is lower than -1 (like temperature)

Draw arrow to show water flow.
9
Two xylem cells (pipes)

• Is there a membrane here?
• No (membranes goneonly walls left)
• Bulk flow (everything together)
• Pressure potential is what counts
• Dont have to calculate water potentials
• Just look at the pressure potential
• -1 and -2

• Which pressure potential is lower?
• -2 is lower than -1 (like temperature)

Draw arrow to show water flow.
10
Ordinary cell next to xylem cell

• Is there a membrane here?
• Yes (for the live cell)
• Water potential is what counts
• Calculate water potentials
• SP PP WP
• Write them in as you go
• -4 1 ?
• -3
• -1 (-1) ?
• 0

-3
-2

• Which water potential is lower?
• -3 is lower than 0 (like temperature)

Draw arrow to show water flow.
11
Thats all

• Just follow all the steps
• One at a time
• In order
• Write, draw, explain
• Let me know if this was helpful
• Tell me if you spot any errors