Plasma MembranesPlasma Membranes

3. Membrane Transport3. Membrane Transport

- Passive Transport- Passive Transport

Moving Through MembranesMoving Through Membranes

• Molecules such as water, CO2, O2 and other Molecules such as water, CO2, O2 and other small molecules can pass easily throughsmall molecules can pass easily through

• Larger molecules and various ions need to go Larger molecules and various ions need to go through transport proteinsthrough transport proteins

• Membranes are differentially permeable – Membranes are differentially permeable – select what passes through & what does notselect what passes through & what does not

• Substances pass in and out of the cell by 4 Substances pass in and out of the cell by 4 main processes:main processes:

Moving Through MembranesMoving Through Membranes

1.1. Diffusion (passive transport)Diffusion (passive transport)

2.2. Osmosis (passive transport)Osmosis (passive transport)

3.3. Active transportActive transport

4.4. Endocytosis and exocytosisEndocytosis and exocytosis

1.1. Diffusion (Passive Transport)Diffusion (Passive Transport)

Passive Transport - Passive Transport - DiffusionDiffusion• Passive transport – movement of materials Passive transport – movement of materials

across a membrane with no energy needacross a membrane with no energy need

• Diffusion: The passive movement of materials Diffusion: The passive movement of materials from regions of high to regions of low from regions of high to regions of low concentrationconcentration

DiffusionDiffusion

• Difference in Difference in concentration called concentration called concentration gradient concentration gradient or diffusion gradientor diffusion gradient

• Always takes place Always takes place when gradient exists when gradient exists

• Continues until particles Continues until particles distributed evenly – distributed evenly – equilibrium reachedequilibrium reached

• Takes place in non-Takes place in non-living and living systemsliving and living systems

Activity - DiffusionActivity - Diffusion

• Add water to a beakerAdd water to a beaker• What do you think will happen to the crystals of What do you think will happen to the crystals of

Potassium Permanganate if you add them to one Potassium Permanganate if you add them to one section of the water (don’t scatter the crystals)?section of the water (don’t scatter the crystals)?

• Predict, Observe, ExplainPredict, Observe, Explain• When you have observed what has occurred, When you have observed what has occurred,

think about what the molecules are then doingthink about what the molecules are then doing• Write up a practical report explaining what you Write up a practical report explaining what you

predicted, what you saw, what happened, and predicted, what you saw, what happened, and any differences between what was predicted and any differences between what was predicted and what occurredwhat occurred

Factors Increasing DiffusionFactors Increasing Diffusion

Diffusion rate is higher when:Diffusion rate is higher when:• The concentration gradient is greatThe concentration gradient is great• Heat is applied (particles move faster)Heat is applied (particles move faster)• Molecules are smallerMolecules are smaller• Movement occurs through a gaseous Movement occurs through a gaseous

medium (particles further apart)medium (particles further apart)

• Water, O2, CO2 and other small uncharged Water, O2, CO2 and other small uncharged particles pass easily through the particles pass easily through the membrane by diffusionmembrane by diffusion

Plasma membranes and Plasma membranes and DiffusionDiffusion

So how do cells manipulate diffusion So how do cells manipulate diffusion for their own benefit?for their own benefit?

Facilitated DiffusionFacilitated Diffusion

• Still requires a Still requires a concentration gradientconcentration gradient

• For charged particles For charged particles and relatively large and relatively large particlesparticles

• Plasma membrane Plasma membrane proteins assist this proteins assist this diffusiondiffusion

• Two types of proteins Two types of proteins involved:involved:- Channel proteins- Channel proteins- Carrier proteins- Carrier proteins

Carrier ProteinsCarrier Proteins

• Open and close areas Open and close areas along the plasma along the plasma membranemembrane

• When open, ions or When open, ions or molecules can pass molecules can pass throughthrough

• They bind to specific They bind to specific molecules or ions on molecules or ions on one side of the one side of the membrane, change membrane, change shape and release shape and release the molecule or ion the molecule or ion on the otheron the other

Channel ProteinsChannel Proteins

• May be open or closedMay be open or closed• Form narrow Form narrow

passageways through passageways through which small ions can which small ions can diffuse rapidly from diffuse rapidly from areas of high to low areas of high to low concentrationsconcentrations

• Only ions of specific Only ions of specific size and shape can size and shape can pass throughpass through

• Channels therefore Channels therefore select which molecules select which molecules the cell does or doesn’t the cell does or doesn’t needneed

QuestionsQuestions

• Complete review questions (passive Complete review questions (passive diffusion/diffusion)diffusion/diffusion)

• What is moving when diffusion occurs?What is moving when diffusion occurs?

• What do you think will happen if the What do you think will happen if the particles are too large or otherwise particles are too large or otherwise unable to pass through the membrane?unable to pass through the membrane?

2. Osmosis (Passive Transport)2. Osmosis (Passive Transport)

OsmosisOsmosis

• Special type of diffusionSpecial type of diffusion• No energy inputNo energy input• Net movement of solvent Net movement of solvent

(usually H2O) across a (usually H2O) across a differentially permeable differentially permeable membranemembrane

• Solvent moves from the Solvent moves from the side of the membrane side of the membrane with a dilute solute (eg with a dilute solute (eg sugar) concentration, to sugar) concentration, to the side of the the side of the membrane with a high membrane with a high solute concentration solute concentration

• Water moves down a Water moves down a concentration gradientconcentration gradient

OsmosisOsmosis

• Osmotic pressure of a solution relates to the Osmotic pressure of a solution relates to the liklihood solvent (usually water) will diffuse into itliklihood solvent (usually water) will diffuse into it

• Solvent moves from an area of low osmotic Solvent moves from an area of low osmotic pressure (low concentration solute) to an area of pressure (low concentration solute) to an area of high osmotic pressure (high concentration solute)high osmotic pressure (high concentration solute)

• When concentrations of solutions separated by a When concentrations of solutions separated by a selectively permeable membrane is the same, selectively permeable membrane is the same, water still moves, but there is equal movement – water still moves, but there is equal movement – net movement is zero, and no volume changesnet movement is zero, and no volume changes

• The result of osmosis is an evening out of solute The result of osmosis is an evening out of solute concentrations on either side of a differentially concentrations on either side of a differentially permeable membrane, by movement of water permeable membrane, by movement of water moleculesmolecules

Tonicity and OsmosisTonicity and Osmosis

• The environment surrounding cells may contain The environment surrounding cells may contain concentration of dissolved solutes that are concentration of dissolved solutes that are equal equal toto, , less thanless than or or greater thangreater than those found within those found within the cell. the cell.

• The relative concentration of solutes is described The relative concentration of solutes is described in terms of in terms of tonicitytonicity. .

• If a cell is in a surrounding environment that is: If a cell is in a surrounding environment that is: isotonicisotonic - there is no net movement of - there is no net movement of

water water between cell and environment.between cell and environment.hypertonichypertonic - this is the area with a higher - this is the area with a higher concentration of solute.concentration of solute.hypotonichypotonic - this is the area with a lower - this is the area with a lower

concentration of solute.concentration of solute.

Tonicity and OsmosisTonicity and Osmosis

• These terms are These terms are dependent on the dependent on the relationship between the relationship between the environments on either environments on either side of the membrane, and side of the membrane, and apply to the environment apply to the environment inside the cell or the inside the cell or the environment outside the environment outside the cell.cell.

•   The key to understanding The key to understanding osmosis and tonicity is to osmosis and tonicity is to remember that remember that water will water will always move toward a always move toward a hypertonic hypertonic environmentenvironment!!

Activity - OsmosisActivity - Osmosis

• Predict, observe, explainPredict, observe, explain• Three workstations have been prepared, with Three workstations have been prepared, with

slides which show red blood cells that have been slides which show red blood cells that have been placed in water, normal saline, and a high salt placed in water, normal saline, and a high salt solutionsolution

• State what you will think will happen, observe what State what you will think will happen, observe what has happened, and explain any differences from has happened, and explain any differences from what you predicted to what you observed.what you predicted to what you observed.

• If your predictions were correct, explain what If your predictions were correct, explain what happened in terms of movement of water.happened in terms of movement of water.

• What do you think would happen if these three What do you think would happen if these three solutions were injected into your bloodstream?solutions were injected into your bloodstream?

Osmosis and Animal CellsOsmosis and Animal Cells• Ideally cells are surrounded by a solution that has an equal Ideally cells are surrounded by a solution that has an equal

solute concentration as the inside of the cell (isotonic)solute concentration as the inside of the cell (isotonic)• Fluids given to patients eg IV drip must be at a Fluids given to patients eg IV drip must be at a

concentration equal to blood plasma so osmosis doesn’t concentration equal to blood plasma so osmosis doesn’t occur into or out of blood cellsoccur into or out of blood cells

• If the plasma becomes more dilute (hypotonic), water will If the plasma becomes more dilute (hypotonic), water will move into blood cells and burst them (haemolysis)move into blood cells and burst them (haemolysis)

• If the plasma becomes more concentrated (hypertonic), If the plasma becomes more concentrated (hypertonic), water will move out of blood cells into plasma (crenation)water will move out of blood cells into plasma (crenation)

Osmosis and Plant CellsOsmosis and Plant Cells

• Turgor of cells supports Turgor of cells supports plants and maintains shape plants and maintains shape and formand form

• Vacuoles in their cells can Vacuoles in their cells can rapidly gain or lose waterrapidly gain or lose water

• Cell wall prevents cell lysis Cell wall prevents cell lysis during turgorduring turgor

• Plasma membrane comes Plasma membrane comes away from the cell wall away from the cell wall during water lossduring water loss

• When this happens, cells When this happens, cells become flaccid and wilting become flaccid and wilting occurs, causing plant to occurs, causing plant to droopdroop

Activity 2 - OsmosisActivity 2 - Osmosis

• Design your own simple experiment to Design your own simple experiment to perform at home which you think shows perform at home which you think shows osmosis occurringosmosis occurring

• Write up a practical report, with labelled Write up a practical report, with labelled diagrams, your aim, method, and diagrams, your aim, method, and discussion of the resultsdiscussion of the results

• Explain why you set up the experiment the Explain why you set up the experiment the way you did, what has occurred, and how way you did, what has occurred, and how you have judged whether the experiment you have judged whether the experiment was a success or notwas a success or not

QuestionsQuestions

• What applications are there for this What applications are there for this information in real life?information in real life?

• What is moving in osmosis?What is moving in osmosis?

• Review questions (osmosis)Review questions (osmosis)

•BioZone questions (osmosis)

Reverse OsmosisReverse Osmosis

• Separation process that uses pressure to force Separation process that uses pressure to force solvent through a semipermeable membranesolvent through a semipermeable membrane

• Solute remains on one side, and pure solvent is Solute remains on one side, and pure solvent is filtered throughfiltered through

• Used most often to produce pure waterUsed most often to produce pure water

Activity – Passive TransportActivity – Passive Transport

• Draw a Venn Diagram to compare Draw a Venn Diagram to compare and contrast the two types of passive and contrast the two types of passive transport - diffusion and osmosistransport - diffusion and osmosis

• Ensure you include concentration Ensure you include concentration gradients, what is moving, the gradients, what is moving, the direction of movement, and anything direction of movement, and anything else you think is relevantelse you think is relevant