UNI Plant Physiology Spring 2005 Water Movement UNI Plant Physiology Spring 2005

Three Rules WP = PP + SP Membrane? Water flows from high to low Yes?…Osmosis happens: WP determines flow No?... Bulk flow happens: PP determines flow Water flows from high to low

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

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

Now do the problem set Don’t go any further in this presentation until you have done everything you can on your own. Reading about solving problems is like reading about swimming. You will drown if you read, then jump in the deep end of the pool.

Done the problem set yet Done the problem set yet? OK, time to check the thinking and the answers. Read and answer the questions before clicking to continue. Watch carefully: something happens with each click. Page Up to go back & see it again.

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.

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.

Two xylem “cells” (pipes) Is there a membrane here? No (membranes gone—only walls left) Bulk flow (everything together) Pressure potential is what counts Don’t 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.

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) = ? -3 -2 Which water potential is lower? -3 is lower than 0 (like temperature) Draw arrow to show water flow.

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