Osmosis and Water Potential

Ch 7 - Principles of Transport/Osmosis and Effects on Cells

Ch 36 Osmosis-Water Potential in plants

Problem:

Permeable to simple sugars but not dissacharides.

Can we answer Q 6 a-e on page 141?

“Cell”: 0.03 M sucrose0.02 M glucose

Environment:0.01 M sucrose0.01 M glucose0.01 M fructose

“Tonicity” drives direction of water movement

• Hypertonic• Hypotonic• Isotonic

Effects on Cells

• Plant cells--What adaptations do plant cell have to deal with water balance?– Vocab: turgid, flaccid, plasmolysis

• Animal cells– Vocab: lysis

Freshwater adaptations that prevent cell lysis

• Freshwater Fish…drink a little, but pee a lot • Protista…contractile vacuole (eg. Paramecium)

Ch 36 - Adaptations for Resource Acquisition

• Private Life of Plants excerpt:Perfect Pumps

What drives the movement of water?

• What is this a picture of? (hint: a major plant organ)

• What adaptations do plants have to control the route water takes?

Three routes of transport• Apoplastic - external to cell membrane, through

walls and spaces• Symplastic - through cytoplasm and plasmodesmata• Transmembrane - passage across cell membranes

and wallsCell wall

Cytosol

PlasmodesmaPlasma membrane

Apoplastic route

Symplastic routeTransmembrane route

Key

ApoplastSymplast

Investigating Solute Movement

• Water follows ions…but how do ions become concentrated.

• Active Transport• We will also discuss

this in relation to the human kidney– Ch. 8 147-151– Ch. 44 936-953

Source vs. Sink

Comparing Xylem and Phloem

Role of Xylem and Phloem

Water Potential

• Tendency of water moves from areas of higher water potential to lower water potential.

• Water potential= pressure potential plus solute potential

Model of Water Potential

Turgor Pressure

• Plant cell walls exert pressure on the cells

• Turgid = Healthy state

Water potential in a Hypertonic Solution

• Why is the cell losing water?

• What is the end result--what happens to the water potential inside/outside the cell?

Water potential in a hypotonic solution?

• What happens to the cell over time?

• Where is the water potential greater to begin?

• Which direction does the water move?

Now let’s go back and see why water moves up the tree?

Loss of water drives movement

• Loss of water from stomata

• Cohesion-tension hypothesis

• Movement by Bulk Flow

• Online - Transpiration Case Study

Regulation of Transpiration

• Where would we find guard cells ?

• Can you explain picture B using the concept of water potential?

Review the Concept of Water Potential

Background research:

•Osmosis Lab Bench

•Case Study 36: How are Water and Solute Potentials Calculated

Lab:• As a class, we are going to compare water

potential of different plant parts:

– Roots, Stems, Tubers, Leaves, Fruit

• Each group will develop a standard curve to estimate the water potential of their assigned plant part.

– You will be able to make a 1 M sucrose solution, and then you will use serial dilutions to make known sucrose standards.

How to use sucrose concentration to solve for water potential?

What will you use for concentration?

• What will your indepedent and dependent variables be?

• What can you use your standard curve to solve for?