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### Plant PhysiologyWater Relations Problem Set

Semi-interactive Key

And Explanations

for use with PowerPoint XP

How To Use this Program

- Start with an unmarked copy of problem set
- Go through the program
- Use mouse, not keyboard (push roller to go back)
- Read the text, clicking to get more
- Fill in values on your problem set as asked
- Check your answers with the program
- Click on links for further explanation
- Click R in the upper right corner of the explanation page to return to where you were

UNI Plant Physiology

Need to review Water Potential?

- What it is
- Units
- Scale (values)
- Factors that make up WP
- Pressure potential
- Solute potential
- Matric potential
- OK? Just click to continue to problems

Click here for next line

UNI Plant Physiology

-6

-10

Problem #1Here you have two cells. Your job is to fill in the missing values for the

water potential factors.

Some values are given. Some values you know from the kind of cell. Others you know from the information given. Still further values you get from arithmetic.

We’ll work through each problem slowly, with your participation, filling in values on your copy. Just click when you want to go onward, starting now.

Humid morning; cells at equilibrium with each other.

UNI Plant Physiology

-10

Problem #1 - aStrategy: First fill in what you know because of what kind of cell it is.

Then we will fill in values based on further information given.

Lastly, we will do the arithmetic to get the remaining values.

The left cell is a (live) leaf mesophyll cell. This tells you its matric potential. Fill it in now on your copy. Click to check your answer on the diagram.

The matric potential of all really wet things is zero.

mesophyll xylem

The right cell is a xylem vessel element, and it is filled with xylem sap, mostly water. This tells you its matric potential. Write in the matric potential for that cell on your copy now then click to check your answer on the diagram.

0

0

0

0

The matric potential here is zero, too,

because the solution in the cell is wet.

UNI Plant Physiology

-6

-10

0

0

Problem #1 - bStrategy: First fill in what you know because of what kind of cell it is.

(Still doing this.)

The right cell is a xylem vessel element, and it is filled with xylem sap, almost pure water.This tells you its solute potential. Fill it in now on your copy. Click to check your answer.

The solute potential of pure water is zero.

This is all the information you can get from the type of cells present. The next step is to use the other information included with the problem.

0

0

0

UNI Plant Physiology

-6

0

-10

0

0

Problem #1 - cStrategy: First we filled in values based on the kinds of cells.

Now we will fill in values based on information given with the problem.

Lastly, we will do the arithmetic to get the remaining values.

The cells are at equilibrium with each other. This means they have the same water potential. Fill in the missing water potential now on your copy. Click to check.

We would expect this type of equilibrium on a humid morning, because the cells would have had plenty of time for the water to move if there was any difference in water potential.

-6

-6

0

Humid morning; cells at equilibrium with each other.

UNI Plant Physiology

-6

-6

0

-10

0

0

Problem #1 - dStrategy: First we filled in values based on the kinds of cells.

Then we filled in values based on information given.

Lastly, we will do the arithmetic to get the remaining values.

WP = PP + SP + MP or Ψ = ψp +ψs + ψm

Fill in the missing values for the left cell now on your copy.

Click to check your answer.

-6 =+4+ (-10) + 0

Now fill in the missing values for the

right cell on your copy. Click to check.

+4

-6

+4

-6

-6 =-6+ 0 + 0

0

Check the arithmetic again and then…

UNI Plant Physiology

-6

-6

+4

-6

0

-10

0

0

Are we finished?Well, not quite. We should go through the final answer and make sure that the proposed numbers are sensible, likely ones. So here we go.

Normal cells have water potentials that are between about -1 and -15 bars. Our value looks reasonable.

Next check the pressure potential: Typically it should be positive

for live cells and negative for xylem. So our answers look good.

The solute potential of mesophyll cells is

always negative, and typically several bars

In magnitude. Ours still looks good.

The matric potential in wet cells (or wet anything else) is zero. Looks OK here.

0

Well, it all looks good, so we can go to

the next problem.

UNI Plant Physiology

-10

Problem #2- aStrategy: First fill in what you know because of what kind of cell it is.

Then we will fill in values based on further information given.

Lastly, we will do the arithmetic to get the remaining values.

The left cell is a (live) leaf mesophyll cell, and the right cell is a xylem vessel element. This tells you their matric potentials. Fill both in now on your copy. Click to check your answer on the diagram.

Wet things have a matric potential of zero.

mesophyll xylem

Now figure out the solute potential. The left (live) cell is given, so you just have to do the xylem cell. Write in its solute potential now on your copy,then click to check your answer on the diagram.

0

Transpiration starting (sunrise). Same cells as above.

0

0

0

0

If you need this explained again, roll the mouse back to Problem 1 – b.

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-10

0

0

0

Problem #2- bStrategy: First we filled in values based on the kinds of cells.

Now we will fill in values based on information given with the problem.

Lastly, we will do the arithmetic to get the remaining values.

If transpiration is taking place, there must be water flow from the xylem to the mesophyll cell. This means the mesophyll cell has a lower water potential than the xylem. Typically the differences are just a couple of bars for nearby cells. Draw an arrow to show the direction of water flow between the cells, then fill in a likely value now on your copy.

Click to check your answer on the diagram.

mesophyll xylem

If you need more explanation on water movement, click here.

-8

0

Transpiration starting (sunrise). Same cells as above.

UNI Plant Physiology

-8

-10

0

0

0

Problem #2- cStrategy: First we filled in values based on the kinds of cells.

Then we filled in values based on information given.

Lastly, we will do the arithmetic to get the remaining values.

WP = PP + SP + MP or Ψw = ψp +ψs + ψm

Fill in the missing values for the left cell now on your copy.

Click to check your answer.

mesophyll xylem

-8 =+2+ (-10) + 0

Now fill in the missing values for the

right cell on your copy. Click to check.

0

+2

-6

+2

-6

-6 =-6+ 0 + 0

Check the arithmetic again and then…

UNI Plant Physiology

-8

+2

-6

-10

0

0

0

Does it make sense?We should go through the final answer and make sure that the proposed

values are sensible, likely ones. So here we go.

Normal cells have water potentials that are between about -1 and -15 bars. Our value looks reasonable. There must be a difference in water potentials if transpiration is taking place. We’ve got that, too.

Next check the pressure potential: Typically it should be positive

for live cells and negative for xylem. So our answers look good.

mesophyll xylem

If you got a negative pressure potential for the

mesophyll, you know that for that cell you

chose a value for the water potential that was

too low.

0

Transpiration starting (sunrise). Same cells as above.

The matric potential should be zero. OK.

We’re ready for the next problem.

UNI Plant Physiology

-8

Problem #3 - aStrategy: First fill in what you know because of what kind of cell it is.

Then we will fill in values based on further information given.

Lastly, we will do the arithmetic to get the remaining values.

The left cell is a (live) leaf mesophyll cell, and the right cell is a xylem vessel element. This tells you their matric potentials. Fill both in now on your copy. Click to check your answer on the diagram.

Wet things have a zero matric potential.

mesophyll xylem

Now figure out the solute potential. The only one you can guess is the xylem cell (though the mesophyll cell has probably not changed much). Write in its solute potential now on your copy,then click to check your answer on the diagram.

Transpiration exceeds water uptake by roots. Leaf mesophyll just wilting. Same cells as above, but later.

0

0

0

0

0

0

0

0

0

0

Xylem solute potentials are typically 0 because

xylem sap is typically almost pure water.

UNI Plant Physiology

-8

0

0

0

Problem #3 - bStrategy: First we filled in values based on the kinds of cells.

Now we will fill in values based on information given with the problem.

Lastly, we will do the arithmetic to get the remaining values.

The mesophyll cell is just wilting, which tells you what its pressure potential is. Fill it in now on your copy. Click to check your answer on the diagram.

-10 =0+ (-10) + 0

All that is left now is the arithmetic. Fill in the missing values for both cells now on your copy.

Click to check your answer.

mesophyll xylem

-8 =-8+ 0 + 0

0

-8

0

Transpiration exceeds water uptake by roots. Leaf mesophyll cell just wilting. Same cells as above, but later.

-10

0

0

0

0

0

Check the arithmetic again and then…

UNI Plant Physiology

-8

0

-8

0

-10

0

0

Are the values reasonable?It is reasonable for a transpiring mesophyll cell to have a lower water potential than the adjacent xylem.

A wilting cell always has 0 turgor (pressure potential), and xylem has a negative pressure potential (sap under tension) during transpiration.

Xylem sap usually has very low levels of solutes, so it has a solute potential of zero.

Matric potential of both cells is zero, as it should be for wet things.

mesophyll xylem

So everything looks OK.

Time for the next problem.

Transpiration exceeds water uptake by roots. Leaf mesophyll cell just wilting. Same cells as above, but later.

0

0

0

0

0

UNI Plant Physiology

Problem #4 - a

Here you have a view of two adjacent root cells and the soil next to one of them.

As usual, your job is to fill in the missing values for the water potential factors.

Strategy: First fill in what you know because of the cell type or soil.

Then values based on other information. Lastly, the arithmetic.

Matric potential is easy for the two cells. Fill the values for the cells in now on your copy. For soil, we’ll have to do some more work (later.)

root xylem root cell soil

Matric potential is zero for wet things.

-5

Now on to filling in what we know about the soil, just because it is normal soil.

-8

0

0

0

0

0

Cells at equilibrium with soil. Not same as cells above.

UNI Plant Physiology

-5

-8

0

0

0

Problem #4 - bSoil has different water relations properties than cells do. Because it is open to

the air, the water is just like that sitting on the lab bench. This tells you its

pressure potential, so write the pressure potential for the soil on your copy now.

Because we use open water as our reference (= zero pressure), water in soil would have the same pressure potential (zero).

The water solution between the particles of most soil is typically quite dilute, with very low concentrations of minerals. This tells you what the solute potential is for the soil water. Fill the values for the cells in now on your copy.

Very dilute solutions have solute potentials of essentially zero.

0

0

0

0

Now on to using the other information

included in the problem.

Cells at equilibrium with soil. Not same as cells above.

UNI Plant Physiology

-5

0

-8

0

0

0

0

Problem #4 - cStrategy: First fill in what you know from the material. Now figure out the

values based on other information. Lastly, the arithmetic.

If the cells both at equilibrium with the soil, they must also be at equilibrium with each other. Fill in the water potential value for both cells on your copy now.

The water potential for all 3 parts of the system is the same: -5.

Now all we have left is the arithmetic and the check of whether the values are reasonable.

-5

-5

-5

-5

Cells at equilibrium with soil. Not same as cells above.

UNI Plant Physiology

root cell

-5 =-5+ 0 + 0

soil

-5 =+3+ (-8) + 0

-5 =0 + 0 + (-5)

root xylem root cell soil

-5

-5

-5

0

-8

0

0

0

0

Problem #4 - dStrategy: First fill in what you know from the material. Now figure out the

values based on other information. Lastly, the arithmetic.

Fill in the missing values for each part. Check your answer after each cell.

The check: All the cell values are reasonable, and similar to others we have seen. For soil, the action is normally in the matric potential, which is what we see here. The water potential of the whole system is at equilibrium.

-5

+3

-5

+3

-5

-5

UNI Plant Physiology

root xylem root cell water

-15

-2

-20

Problem #5 - aHere you have two adjacent root cells in shallow salty water (tide flat).

As usual, your job is to fill in the missing values for the water potential factors.

Strategy: First what you know because of the type of cell or surroundings. Then values based on other information. Lastly, the arithmetic.

Matric potential is easy for all three. Fill the values in now on your copy.

Matric potential is zero for wet things.

-5

Now on to filling in more that we know about the cells and the water.

-8

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Transpiration is going on.

0

0

0

UNI Plant Physiology

root xylem root cell water

-15

-2

-20

0

0

0

Problem #5 - bStrategy: Still working on what you know because of the type of cell or surroundings. Then values from other information. Lastly, arithmetic.

There’s nothing more we can do with the cells, but the water is open to the atmosphere, so it has the same pressure potential as water in soil or on the lab bench. Fill in this value for the pressure potential of the water now on your copy.

The pressure potential of open water is zero, just as it is in soil.

-5

Now on to filling in more by using the extra information given with the problem.

0

0

-8

0

0

0

0

0

0

0

0

0

0

Transpiration is going on.

0

0

UNI Plant Physiology

root xylem root cell salty water

-15

0

-2

-20

0

0

0

Problem #5 – cStrategy: First working on what you know because of the type of cell or surroundings. Then values fromother information. Lastly, arithmetic.

Transpiration will move water from the surroundings to the root cell, and then into the root xylem. This tells you that the water potential gets lower along that path (that’s why the water moves). Draw in arrows showing the water movement, and put in likely values for the cell water potentials now on your copy.

Water moves from higher to lower water potential.

-19

-17

-19

-17

-5

Now all we have left is the arithmetic.

-8

0

0

0

0

0

0

0

0

0

0

Transpiration is going on.

0

0

UNI Plant Physiology

root cell

shallow salty water

-19 =-17+ (-2) + 0

-17 =+3+ -20 + 0

-15 = 0 +(-15)+ 0

root xylem root cell salty water

Problem #5 – dStrategy: First working on what you know because of the type of cell or surroundings.Then values from other information. Lastly, arithmetic.

On your copy, now fill in the missing values for the water potential factors, one item at a time, moving from left to right. Then click to check.

All we have left to do is checking that the numbers make sense.

-5

-19

-17

-15

-17

+3

-17

+3

0

-8

0

-2

-15

0

0

-20

0

0

-15

0

0

0

0

0

0

0

0

0

0

UNI Plant Physiology

root xylem root cell shallow salty water

Does it make sense?Xylem typically has negative pressure potential. The solute potential here is not zero, but that can be explained by the salty water the plant is in. The xylem sap has taken in some of that salt. Everything looks OK.

Live cells usually have positive pressures. OK here.

In shallow water the pressure should be zero. In salty water the solute potential should be negative. Looks good.

Matric potential should be zero in all the wet parts of the system.

-5

There should be a gradient of water potential if there is transpiration. OK here.

-19

-17

-15

-17

+3

0

-8

0

-2

0

0

-20

0

0

-15

0

0

0

0

0

0

0

0

0

0

Time for the next problem.

Transpiration is going on.

UNI Plant Physiology

Problem #6 - a

Here you have two adjacent root cells in saline (salty) soil. As usual, your job is to fill in the missing values for the water potential factors.

Strategy: What you know because of the type of cell or surroundings.

Matric potential is easy for the cells. We’ll deal with the soil later. Fill the values of the matric potentials for the cells in now on your copy.

root xylem root cell saline soil

Matric potential is zero for wet things. (The soil isn’t wet.)

Now fill in a likely value for the soil pressure potential.

-5

-8

0

0

-8

Water in soil, open to the atmosphere, always has a pressure potential of zero.

0

-4

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Transpiration is going on.

Time for the next step.

UNI Plant Physiology

Problem #6 - b

Still working on what you know because of the type of cell or surroundings.

We know something about the pressure potential of live cells, even if we don’t know the exact value. Fill in a reasonable number for the root cell pressure potential.

root xylem root cell saline soil

Other values are possible, but live cell pressure potential is always zero (for wilting cells) or positive (the rest).

-8

+2

+2

0

-4

We have more work to do,

still based on the kinds of cells.

0

0

UNI Plant Physiology

+2

0

-4

0

0

Problem #6 - cStill working on what you know because of cell type or surroundings.

Xylem solute potential probably isn’t zero, because the plant is in saline soil. Now fill in a reasonable value for the xylem solute potential.

Xylem sap in plants in saline soil is likely to be around -1 bar (it might be a bit lower), because of the soil salt level.

root xylem root cell saline soil

At last it is time to use the other informationto get the remaining values.

-1

-1

Transpiration is going on.

UNI Plant Physiology

+2

0

-1

-4

0

0

Problem #6 - dStrategy: Now the values fromother information.

Transpiration sets up a gradient of water potential. The water will be moving from the soil to the root cell to the xylem. Fill in arrows showing water movement, and reasonable values of water potential for the cells.

root xylem root cell saline soil

Other values are possible, but water always flows from higher to lower water potential.

-12

-10

-12

-10

Time for the arithmetic.

Transpiration is going on.

UNI Plant Physiology

root xylem

saline soil

-10 =+2+ (-12) + 0

-12 =-11+ (-1) + 0

-8 = 0 +(-4)+ (-4)

root xylem root cell saline soil

-12

-10

-8

+2

0

-1

-4

0

0

Problem #6 – eNow the arithmetic.

Fill in the missing values for each part. Check your answer after each cell.

Time for the final check.

Try your own before proceeding.

-11

-11

-12

-12

-4

-4

UNI Plant Physiology

root xylem root cell saline soil

-12

-10

-8

+2

0

-1

-4

0

0

Does it make sense?Xylem typically has negative pressure potential. The solute potential here is not zero, but that can be explained by the saline soil the plant is in. The xylem sap has taken in some of that salt. Everything looks OK.

Live cells usually have positive pressures. OK here.

In any soil the pressure should be zero. In saline soil the solute potential should be negative. In soil that isn’t really wet, the matric potential should be negative. Looks good.

root xylem root cell saline soil

There is a gradient of water potential that drives transpiration. Other values are possible, but water always flows from higher to lower water potential.

-11

-12

-4

Transpiration is going on.

UNI Plant Physiology

+5

-3

Problem #7 - aHere you have two adjacent root cells in a highly saline environment.

Strategy: What you know because of the type of cell or surroundings.

Matric potential is easy for the cells. Fill the values for the cells in now.

Matric potential is zero for wet things.

root xylem root cell

Now use the information given to put in the water potential for the root cell.

-8

Cells are often in water potential equilibrium (same) before dawn.

-8

0

0

Plant growing in very saline soil. Cells are at equilibrium with each other (before dawn).

0

0

Time for the arithmetic.

UNI Plant Physiology

root cell

-8 =-5+ -3 + 0

-8 =+5+ (-13) + 0

-8

+5

-3

Problem #7 - bNow the arithmetic. Fill in the missing values for each part. Check your answer after each cell.

root xylem root cell

Now check the values to make sure they make sense, given the type of cell and the conditions.

-8

-5

-5

-13

-13

Plant growing in very saline soil. Cells are at equilibrium with each other (before dawn).

0

0

UNI Plant Physiology

+5

-3

Does it make sense?Xylem typically has negative pressure potential. The solute potential here is quite low, but that can be explained by the extremely salty environment the plant is in. The xylem sap has taken in quite a bit of that salt. Everything looks OK.

The live cell has a positive pressures, and a quite low solute potential, which we might expect in the highly saline environment. OK here.

root xylem root cell

The cell water potentials aren’t very low, so the soil must be quite moist, even thought it is quite salty. This often happens in areas with ample irrigation with saline water.

-8

-5

-13

Plant growing in very saline soil. Cells are at equilibrium with each other (before dawn).

0

0

UNI Plant Physiology

Problem #8 - a

Here you have two adjacent root cells in a highly saline environment.

What you know because of the type of cell or surroundings. Fill in the values for matric potential of the cells now.

Now use the information given to figure out more. These are the same cells as above, so solute potentials will be about the same. Put these in now.

root xylem root cell

-13

-3

-13

-3

0

0

0

0

Same plant and soil as cells in previous problem. Transpiration is going on.

Time for the arithmetic.

UNI Plant Physiology

-13

0

0

Problem #8 - bNow use the information given to figure out the effects of transpiration.

You have to figure out which way the water is moving as transpiration is going on, and what are likely values for the water potential. These are the same cells as the previous problem, but the transpiration may have dragged their water potentials down a little lower.

Draw an arrow showing the direction of transpiration, then put in plausible values for the water potential.

root xylem root cell

Water will move from soil (not shown) into the live root cell, then into the xylem for transport upward. There are other possible values for water potentials, but water will always move from higher to lower values. There are other limits on the possible values, too. If you exceed them, your other values won’t make sense.

-12

-10

-12

-10

Same plant and soil as cells in previous problem. Transpiration is going on.

Nothing left but arithmetic.

UNI Plant Physiology

root cell

-12 =-9+ (-3) + 0

-10 =+3+ (-13) + 0

-12

-10

-3

-13

0

0

Problem #8 - cThe arithmetic should be easy by now. Fill it in and check your values.

Does it make sense? Well, you have a water potential gradient, and zero matric potential, which is what you expect.

The other thing to check is that the pressure potential is negative in the xylem and positive in the live cell.This is what places limits on the water potential. You can’t have the live cell with a water potential of -20 here, because that would give you a negative pressure potential in a live cell (impossible).

root xylem root cell

-9

+3

-9

+3

Same plant and soil as cells in previous problem. Transpiration is going on.

On to the last problem.

UNI Plant Physiology

Problem #9 - a

We’re up in the top of the tree now. With the same xylem sap as in the previous problem. The soil has now dried substantially.

What you know because of the type of cell or surroundings. Fill in the values for matric potential of the cells now.

Now use the information given to figure out more. The xylem (right here) is the same as in the problem above (on left), so its solute potential will be the same. Put the value in now.

Same plant and soil as in previous problem. The soil is at -15 bars, the whole plant is at equilibrium with the soil (night), and the leaf is wilting.

-3

-3

-3

0

0

0

0

Almost done.

UNI Plant Physiology

root cell

-15 =+0+ (-15) + 0

-15 =+(-12)+ (-3) + 0

leaf cell xylem

-3

0

0

Problem #9 - bContinue using the information given to figure out more. The equilibrium between the cells and the soil is next. Put values for cell water potentials in now.

Use the “wilting” information to determine the leaf cell pressure potential. Fill in the value now.

Wilting tissue always has a pressure potential of zero.

Now do the arithmetic, one cell at a time.

-15

-15

-15

-15

Same plant and soil as in previous problem. The soil is at -15 bars, the whole plant is at equilibrium with the soil (night), and the leaf is wilting.

0

-12

0

-12

-15

-15

One last check that the values are sensible.

UNI Plant Physiology

-15

-15

0

-12

-15

-3

0

0

Does it make sense?The wilting live cell has zero pressure potential, and the xylem has a negative pressure potential. Everything looks OK there.

Cells in equilibrium have the same water potential. The matric potential is zero. Looks OK here.

The low solute potential in the xylem is believable because the plant is growing in very saline soil.

Everything looks fine. You’re done!

You can go back to review any thing and any time you wish.

Same plant and soil as in previous problem. The soil is at -15 bars, the whole plant is at equilibrium with the soil (night), and the leaf is wilting.

UNI Plant Physiology

Thank You

Thank you for testing this program. If you find any errors, please email them to me at bergv@uni.edu. If you have any comments, please do the same. Please share the folder (program, problem set and viewer) with your colleagues and students.

Because this program has my name on it, please DO NOT modify it. I will try to correct errors and make improvements as fast as possible, and will post the new version on my download web page, with the date of the latest correction.

UNI Plant Physiology

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