A Cell Mitochondrion Nucleus Selectively permeable cell membrane Cytoplasm

A CellA Cell

Mitochondrion

Nucleus

Selectively permeable cell membrane

Cytoplasm

Selective Selective MembraneMembrane

Why do cells need to transport Why do cells need to transport materials across the cell materials across the cell

membrane?membrane?• Cells need to obtain various Cells need to obtain various

substances in order to carry out life substances in order to carry out life processesprocesses

• What are some of the substances that What are some of the substances that they need to obtain?they need to obtain?

• e.g. nutrients, oxygen, water, etc.e.g. nutrients, oxygen, water, etc.

Why do cells need to transport Why do cells need to transport materials across the cell materials across the cell

membrane?membrane?

• Cells also need to get rid of Cells also need to get rid of substances that are useless and substances that are useless and harmful to themharmful to them

• What are some of the substances that What are some of the substances that must be removed?must be removed?

• e.g. carbon dioxide, metabolic e.g. carbon dioxide, metabolic wastes, etc.wastes, etc.

Transportation of Transportation of MaterialsMaterials

There are 3 different processes for There are 3 different processes for transporting materials in and out of a transporting materials in and out of a cell:cell:

• DiffusionDiffusion• OsmosisOsmosis• Active TransportActive Transport

DIFFUSIONDIFFUSION

Hi. I am Moley. Hi. I am Moley. I am a gas I am a gas

molecule. I am molecule. I am constantly constantly

moving around. moving around. This is because This is because

I possess I possess kinetic energykinetic energy. .

Here I am with my Here I am with my brothers and sisters. brothers and sisters. Notice that we are all Notice that we are all

cramped to one side of cramped to one side of the area. In other the area. In other

words, there is a words, there is a HIGH HIGH CONCENTRATIONCONCENTRATION of of

molecules on the left molecules on the left side of the area.side of the area.

Area of High ConcentrationArea of High Concentration

Well, since we are Well, since we are moving all the moving all the time, we will time, we will

eventually spread eventually spread out to cover the out to cover the rest of the area. rest of the area. That is, we will That is, we will move along the move along the concentration concentration

gradientgradient, from an , from an area of area of HIGH HIGH

CONCENTRATIONCONCENTRATION to to an area of an area of LOW LOW

CONCENTRAIONCONCENTRAION!!

Area of High ConcentrationArea of High ConcentrationArea of Low ConcentrationArea of Low Concentration

CONCENTRATION GRADIENTCONCENTRATION GRADIENT

EQUILIBRIUMEQUILIBRIUM – Particles are evenly distributed – Particles are evenly distributed

DiffusionDiffusion

• Diffusion is the net movement of Diffusion is the net movement of the particles of a substance from the particles of a substance from a region of a region of higher concentrationhigher concentration to a region of to a region of lower lower concentrationconcentration

• It is a It is a passivepassive process and no process and no external energy is requiredexternal energy is required

• It can occur in a liquid or It can occur in a liquid or gaseous mediumgaseous medium

We can also We can also pass through a pass through a

selectively selectively permeable permeable membranemembrane

because we are because we are so small!!!so small!!!

Area of High ConcentrationArea of High Concentration





EQUILIBRIUMEQUILIBRIUM – Particles are evenly distributed – Particles are evenly distributed

DiffusionDiffusion

A small amount of ink isA small amount of ink isadded to a beaker of added to a beaker of water. What do you water. What do you think will happen?think will happen?

DiffusionDiffusion

- Can you explain the Can you explain the color change?color change?

- Do you think the ink Do you think the ink particles will continueparticles will continue to move even after they to move even after they have spread out evenlyhave spread out evenly in the water?in the water?

- Will the result be the Will the result be the same if this is carried out same if this is carried out in hot water? in hot water?

Factors Affecting Factors Affecting the Rate of Diffusionthe Rate of Diffusion

• Molecular sizeMolecular size – will small or large – will small or large particles diffuse faster?particles diffuse faster?

• Concentration gradientConcentration gradient – will diffusion – will diffusion occur more rapidly if there is a large occur more rapidly if there is a large or small difference in concentration or small difference in concentration between two regions?between two regions?

• Distance of diffusionDistance of diffusion – will diffusion – will diffusion be faster or slower if the distance of be faster or slower if the distance of diffusion is long?diffusion is long?


• MediumMedium – is diffusion faster in a – is diffusion faster in a gaseous or liquid medium?gaseous or liquid medium?

• Surface areaSurface area – will diffusion – will diffusion occur faster in a large or small occur faster in a large or small surface area?surface area?



• MediumMedium – is diffusion faster in – is diffusion faster in gaseous or liquid medium?gaseous or liquid medium?

• Surface areaSurface area – will diffusion – will diffusion occur faster in a large or small occur faster in a large or small surface area?surface area?

• TemperatureTemperature – will diffusion be – will diffusion be faster under high or low faster under high or low temperature?temperature?

Examples of DiffusionExamples of Diffusion

• Exchange of gases (i.e. oxygen and Exchange of gases (i.e. oxygen and carbon dioxide) in the air sacs of carbon dioxide) in the air sacs of lungslungs

• Absorption of digested food in the Absorption of digested food in the gutgut

• The detection of smell e.g. perfumeThe detection of smell e.g. perfume• The movement of carbon dioxide The movement of carbon dioxide

through the stomata during through the stomata during photosynthesisphotosynthesis

OSMOSISOSMOSIS

OsmosisOsmosis

• Osmosis is the net movement Osmosis is the net movement (i.e. diffusion) of water (i.e. diffusion) of water molecules from a less molecules from a less concentrated solution (with a concentrated solution (with a higher water potentialhigher water potential) to a ) to a more concentrated solution (with more concentrated solution (with a a lower water potentiallower water potential) through ) through a selectively permeable a selectively permeable membranemembrane

This is a water moleculeThis is a water molecule

This is a sucrose moleculeThis is a sucrose molecule

Region A – Dilute sucrose solutionRegion A – Dilute sucrose solutionRegion B – Concentrated sucrose solutionRegion B – Concentrated sucrose solution

This is a water molecule

This is a sucrose molecule

Region A – Dilute sucrose solutionRegion A – Dilute sucrose solutionRegion B – Concentrated sucrose solutionRegion B – Concentrated sucrose solution

INVESTIGATION #1INVESTIGATION #1

Illustration of osmosis using a Illustration of osmosis using a dialysis tubingdialysis tubing

Introduction to Introduction to InvestigationInvestigation

• In this experiment, osmosis will In this experiment, osmosis will be demonstrated by using a be demonstrated by using a dialysis tubing, which acts as a dialysis tubing, which acts as a selectively permeable membraneselectively permeable membrane

ProcedureProcedure

• Please Please refer to refer to pages 83 pages 83 and 84 in and 84 in your your ARISTO ARISTO text book text book

Results TableResults Table

TimeTime Distance from Distance from initial markinitial mark

After 5 minutesAfter 5 minutes




Plot the data on a Plot the data on a graphgraph

Dis

tan

ce r

isen

by t

he

su

cro

se s

olu

tion

Time (Mins.)

What will the graph look like?

Can you predict the results in Can you predict the results in the following situations?the following situations?

Treatment

Inside tubing In beaker Change in level

1 Sucrose solution

Distilled water

Rises

2 Distilled water Sucrose solution

?

3 Concentrated sucrose solution

Distilled water

?

4 Distilled water Distilled water

?

Variations to the Variations to the ExperimentExperiment

• Instead of dialysis tubing, we Instead of dialysis tubing, we can also use living tissues, can also use living tissues, such as potatoes, to such as potatoes, to illustrate the process of illustrate the process of osmosisosmosis

Variations to the Variations to the ExperimentExperiment

What do you think is the result of this experiment?

Water PotentialWater Potential• Water potential is represented by the Greek Water potential is represented by the Greek

letter “psi”letter “psi”• A measure of the free energy of water or the A measure of the free energy of water or the

energy for water molecules in a solution to energy for water molecules in a solution to move aboutmove about

• Water potential is dependent on the proporWater potential is dependent on the proportion of free water molecules in a solution (frtion of free water molecules in a solution (free water molecules = water molecules that ee water molecules = water molecules that are not engaged with other molecules)are not engaged with other molecules)

Water PotentialWater Potential

• The water potential of pure The water potential of pure water is defined as zerowater is defined as zero

• If solutes are dissolved in water, If solutes are dissolved in water, the proportion of free water the proportion of free water molecules will decrease. The molecules will decrease. The water potential will also water potential will also decrease to less than zerodecrease to less than zero

Water PotentialWater Potential

• A concentrated solution has a A concentrated solution has a lower water potential than a lower water potential than a dilute solutiondilute solution

• The net movement of water The net movement of water molecules is always from a molecules is always from a region of region of HIGHERHIGHER water potential water potential to a region of to a region of LOWERLOWER water water potentialpotential

TonicityTonicity

• Osmotic movements across cell Osmotic movements across cell membranes are affected by the membranes are affected by the tonicitytonicity: the relative : the relative concentrations of solutes in 2 concentrations of solutes in 2 fluids, e.g. the cytoplasm of a fluids, e.g. the cytoplasm of a cell and the fluid outside the cellcell and the fluid outside the cell

TonicityTonicity

• We are going to use a We are going to use a red blood red blood cellcell as an example. On a piece of as an example. On a piece of paper, draw three beakers. In paper, draw three beakers. In each of the beaker, add a RBC. each of the beaker, add a RBC. We will discuss what happen to We will discuss what happen to the RBC when it is put into 3 the RBC when it is put into 3 different types of solutions of different types of solutions of different concentrations of different concentrations of sodium chloride (i.e. salt)sodium chloride (i.e. salt)

IsotonicIsotonic

CELLCELL

Salty WaterSalty WaterThe water potentialThe water potentialinside the cell is theinside the cell is thesame as that outside same as that outside the cell. There is no the cell. There is no net movement of water net movement of water into or out of the cellinto or out of the cell

HypertonicHypertonic

CELLCELL

Very Salty WaterVery Salty WaterThere is less water There is less water molecules outside the molecules outside the cell, and therefore the cell, and therefore the solution outside has a solution outside has a lower water potential lower water potential than that of the cellthan that of the cell

What will happen to What will happen to the cell?the cell?

HypotonicHypotonic

CELLCELL

Pure WaterPure WaterThere is more water There is more water molecules outside the molecules outside the cell, and therefore the cell, and therefore the solution outside has a solution outside has a higher water potential higher water potential than that of the cell.than that of the cell.

What will happen to What will happen to the cell?the cell?

Effects of Osmosis on Plant Effects of Osmosis on Plant CellsCells

Plant cells placed in a hypertonic solution will undergo Plant cells placed in a hypertonic solution will undergo plasmolysisplasmolysis, , a condition where the plasma membrane pulls away from the cell wall a condition where the plasma membrane pulls away from the cell wall as the cell shrinks. The cell wall is rigid and does not shrink.as the cell shrinks. The cell wall is rigid and does not shrink.

Turgid CellsTurgid Cells Flaccid CellsFlaccid Cells

Effects of Osmosis on Animal Effects of Osmosis on Animal CellsCells



Shrinking RBCShrinking RBC Swelling RBCSwelling RBC

Active Active TransportTransport

Active TransportActive Transport

• Some solutes have a higher Some solutes have a higher concentration inside the cell than concentration inside the cell than outside so they have to cross the outside so they have to cross the membrane membrane againstagainst the concentration the concentration gradient. These solutes need to gradient. These solutes need to enter the cell by means of enter the cell by means of active active transporttransport

• Why is this called Why is this called ACTIVEACTIVE transport? transport?

Cell membraneCell membrane

Low concentration Low concentration outside the celloutside the cell

High concentration High concentration inside the cellinside the cell


Cell Cell membranemembrane














Cell Cell membranemembrane











What is this???What is this???



• Active transport requires special Active transport requires special proteprotein carriersin carriers. These carriers are embedd. These carriers are embedded within the cell membraneed within the cell membrane

• Active transport also requires energy Active transport also requires energy obtained from respirationobtained from respiration

• The energy is used to change the The energy is used to change the shape of the protein carriers so shape of the protein carriers so that the molecules can attach to that the molecules can attach to the carriers for transportationthe carriers for transportation


• The process of active transport The process of active transport is useful when there is no is useful when there is no concentration gradient or when concentration gradient or when diffusion is too slow for the diffusion is too slow for the transportation of substancestransportation of substances

Examples of Active Examples of Active TransportTransport

• Nutrients are actively Nutrients are actively transported into the small transported into the small intestineintestine

• Substances that are useful to the Substances that are useful to the body are actively reabsorbed body are actively reabsorbed into the blood vessels into the blood vessels surrounding the kidney tubulessurrounding the kidney tubules

• Root hairs actively absorb Root hairs actively absorb mineral salts from the soilmineral salts from the soil

Comparison of Comparison of Passive and Active Passive and Active

TransportTransport

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A Cell Mitochondrion Nucleus Selectively permeable cell membrane Cytoplasm