Osmosis and Water Potential

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

Ch 36 Osmosis-Water Potential in plants

Problem:

“Cell”: 0.03 M sucrose0.02 M glucose

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

Permeable to simple sugars but not dissacharides.

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

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“Tonicity” predicts direction of water movement

• Hypertonic• Hypotonic• Isotonic

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Effects on Cells

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

• Animal cells– Vocab: lysis

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Freshwater organisms--Unity and Diversity--Dealing with Water

Balance• Freshwater Fish…must osmoregulate and do not

drink (more later…)• Protista…contractile vacuole (eg. Paramecium)

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Ch 36 - Adaptations for Resource Acquisition

• Private Life of Plants excerpt: Water Transport in Plants

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private life of plants photosynthesis

Ch 36 - Transport in Vascular Plants

• Long distance transport by xylem (see pg 745)

•Tracheids

•Vessel elements

• Cell-to-cell transfer

• Individual cell uptake

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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

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?

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Investigating Solute Movement• Water follows ions…but how do ions become concentrated.• Active Transport

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Water Potential

• Water moves from higher water potential to lower water potential.

• Water potential= pressure potential plus solute potential

Model of Water Potential

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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?

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Loss of water drives movement

• Loss of water from stomata

• Cohesion-tension hypothesis

• Movement by Bulk Flow

• Online - Transpiration Case Study

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Regulation of Transpiration

• Where would we find guard cells ?

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

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Review the Concept of Water Potential

• As a Class--Case Study 36: How are Water and Solute Potentials Calculated?

• On your own: Osmosis Lab Bench