Cells and Their Cells and Their EnvironmentEnvironment

BiologyBiology

Chapter 3Chapter 3

R. GilbertsonR. Gilbertson

HomeostasisHomeostasis

Adjustments made by an Adjustments made by an organism to changing organism to changing

conditionsconditionsBalance between life Balance between life

activities and the activities and the conditions which affect itconditions which affect it

HomeostasiHomeostasiss

• A A dynamic balancedynamic balance between an organism between an organism and its environment.and its environment.

• The balance is maintained by regulating The balance is maintained by regulating what gets into and out of the cell.what gets into and out of the cell.

• There is a range of conditions through There is a range of conditions through which a cell can exist and adjust which a cell can exist and adjust ((tolerance rangetolerance range).).

• Said to be dynamic because the set point Said to be dynamic because the set point of the balance is constantly changing as of the balance is constantly changing as conditions inside and outside the cell conditions inside and outside the cell change.change.

Homeostasis: Occurs at Homeostasis: Occurs at many levelsmany levels

• Behavioral changes – entire organism Behavioral changes – entire organism adjusts to changesadjusts to changes

• Organs work together to maintain the Organs work together to maintain the best internal environment.best internal environment.– Heart pumps blood to all parts of the body Heart pumps blood to all parts of the body

carrying food and oxygen to all tissuescarrying food and oxygen to all tissues– Exercise causes increases in heart rate due to Exercise causes increases in heart rate due to

increased demand for energy and oxygen.increased demand for energy and oxygen.• Cells within a multicellular organism Cells within a multicellular organism

must maintain a balance with the must maintain a balance with the surrounding fluids.surrounding fluids.

• Unicellular organisms must maintain a Unicellular organisms must maintain a constant internal environment only constant internal environment only within the limits of environmental within the limits of environmental changeschanges

Needs of a Needs of a CellCell

Homeostasis and the Homeostasis and the Plasma MembranePlasma Membrane

• Living condition is dependent on the Living condition is dependent on the movement of materials into and out of movement of materials into and out of the cell.the cell.– Food, water, oxygen and other materials Food, water, oxygen and other materials

must move into the cell.must move into the cell.– Carbon dioxide, nitrogenous wastes and Carbon dioxide, nitrogenous wastes and

other materials must move out of the cell.other materials must move out of the cell.– All materials must somehow pass through All materials must somehow pass through

the plasma membrane.the plasma membrane.• Random KE causes molecules to bump Random KE causes molecules to bump

into the membrane at random, into the membrane at random, sometimes they have enough energy to sometimes they have enough energy to pass through.pass through.

• Different materials pass through the Different materials pass through the membrane at different rates.membrane at different rates.

Passive Transport• Any process whereby molecules Any process whereby molecules

are moved across a membrane are moved across a membrane without the expenditure of energy.without the expenditure of energy.

• Particles are generally moved from Particles are generally moved from an area of greater concentration an area of greater concentration to an area of lesser concentration.to an area of lesser concentration.

• Movement of molecules is Movement of molecules is required to maintain homeostasis.required to maintain homeostasis.

Energy

Three types of Three types of Passive Passive

TransportTransport

DiffusionDiffusion

OsmosisOsmosis

Facilitated Facilitated DiffusionDiffusion

Entropy vs. EnthalpyEntropy vs. Enthalpy• EntropyEntropy – the tendency of a – the tendency of a

system left alone to become more system left alone to become more disordered, results from random disordered, results from random effects and causes diffusion effects and causes diffusion (passive)(passive)

• EnthalpyEnthalpy – the creation of order – the creation of order out of chaos with the expenditure out of chaos with the expenditure of energy, causes matter to of energy, causes matter to become more organized (active)become more organized (active)

DiffusionDiffusion• Brownian Motion – random movement of Brownian Motion – random movement of

particles – cause of diffusion particles – cause of diffusion (temperature dependent) said to be (temperature dependent) said to be entropic. entropic.

• Motion caused by kinetic energy of Motion caused by kinetic energy of particles.particles.

• Slight in solids, more in liquids, greatest Slight in solids, more in liquids, greatest in gases.in gases.

• Particles tend to move in straight lines Particles tend to move in straight lines until they collide with other particles.until they collide with other particles.

• Results in a gradual spreading out of Results in a gradual spreading out of molecules.molecules.

DiffusioDiffusion n Passive Passive TransportTransport

• The movement of molecules from an area of The movement of molecules from an area of higher higher concentrationconcentration to an area of to an area of lesser concentrationlesser concentration..

• Molecules are in constant motion, they are Molecules are in constant motion, they are constantly colliding, the collisions are perfectly constantly colliding, the collisions are perfectly elastic so energy is conserved but direction elastic so energy is conserved but direction changes.changes.

• Creates a tendency for molecules to spread out.Creates a tendency for molecules to spread out.

Simple DiffusionSimple Diffusion

• Requires Requires NONO energyenergy

• Molecules Molecules move from move from area of area of HIGH HIGH to LOWto LOW concentratioconcentrationn

Diffusion of LiquidsDiffusion of Liquids

Factors Effecting Factors Effecting DiffusionDiffusion

Concentration GradientConcentration Gradient – more – more particlesparticles

TemperatureTemperature – faster moving – faster moving particlesparticles

PressurePressure – more energetic – more energetic collisionscollisions

Diffusion Across a Diffusion Across a MembraneMembrane

• PermeablePermeable – describes a membrane through – describes a membrane through which certain molecules can pass freely.which certain molecules can pass freely.

• ImpermeableImpermeable – describes a membrane – describes a membrane through which certain molecules cannot through which certain molecules cannot pass.pass.

• Semi-permeableSemi-permeable – describes a membrane – describes a membrane which allows some molecules to pass freely which allows some molecules to pass freely and prevents the passage of others, based and prevents the passage of others, based primarily on the size of the particles.primarily on the size of the particles.

• Selectively permeableSelectively permeable – describes a – describes a membrane which not only allows some membrane which not only allows some molecules to pass through it and prevents molecules to pass through it and prevents others, but also regulates the rate and others, but also regulates the rate and direction of movement. direction of movement.

Factors which affect Factors which affect permeability of the plasma permeability of the plasma

membranemembrane• Structure of the membraneStructure of the membrane – folds, spaces, – folds, spaces,

openings, and specific proteinsopenings, and specific proteins• Size of the particlesSize of the particles, smaller are more likely , smaller are more likely

to pass through, large molecules are less to pass through, large molecules are less likely to pass throughlikely to pass through

• The chemical makeup of the particles.The chemical makeup of the particles.– HH22O, OO, O22, CO, CO22, all pass through freely, all pass through freely– If soluble in lipids it may pass through freelyIf soluble in lipids it may pass through freely

• Solubility of particles in waterSolubility of particles in water – generally will – generally will not pass through if insoluble.not pass through if insoluble.

• Conditions inside and outside the cellConditions inside and outside the cell – – temperature, pressure, and concentration of temperature, pressure, and concentration of solutes.solutes.

DiffusionDiffusion• The movement of molecules from an area of The movement of molecules from an area of

high concentration to an area of lower high concentration to an area of lower concentrationconcentration

• Concentration gradientConcentration gradient – a difference in the – a difference in the concentration of a substance across a space.concentration of a substance across a space.

• EquilibriumEquilibrium – condition in which the – condition in which the concentration of a substance is equal concentration of a substance is equal throughout a space.throughout a space.

• If left alone any system of molecules will If left alone any system of molecules will reach equilibrium. Molecules continue to reach equilibrium. Molecules continue to move but there is no net change in move but there is no net change in concentration.concentration.

Dynamic Dynamic EquilibriumEquilibrium

The continuous The continuous movement of movement of

particles, but with particles, but with NO overall change in NO overall change in

concentration.concentration.

Factors which affect Factors which affect diffusion ratesdiffusion rates

• Concentration gradient – the higher Concentration gradient – the higher the difference between regions the the difference between regions the higher the speed of diffusion.higher the speed of diffusion.

• Changes in temperature – increases Changes in temperature – increases in temp cause increases in KE of the in temp cause increases in KE of the particles so the rate of diffusion particles so the rate of diffusion increases, and vice versa.increases, and vice versa.

• Pressure differences – act to push Pressure differences – act to push particles from one side to the other.particles from one side to the other.

• Diffusion pressure – a combination of Diffusion pressure – a combination of all of the above.all of the above.

Diffusion in a cellDiffusion in a cell• Many substances such as molecules Many substances such as molecules

and ions dissolved in the cytoplasm and ions dissolved in the cytoplasm and in the fluid outside the cell enter and in the fluid outside the cell enter or leave by diffusion.or leave by diffusion.

• There is almost always a difference There is almost always a difference between the concentration of these between the concentration of these molecules inside and outside the cell, molecules inside and outside the cell, creating a concentration gradientcreating a concentration gradient

• Diffusion is always down hill from high Diffusion is always down hill from high to low concentration.to low concentration.

• The substance must be able to pass The substance must be able to pass through the membrane.through the membrane.

Diffusion through a Diffusion through a MembraneMembrane

Cell membrane

Solute moves DOWN concentration gradient (HIGH to LOW)

OsmosisOsmosisDeals only with Deals only with WATERWATER

Refers to the diffusion of Refers to the diffusion of WATERWATER through a through a

selectively permeable selectively permeable membranemembrane

Osmosis – diffusion of water Osmosis – diffusion of water across a selectively across a selectively

permeable membrane.permeable membrane.

Osmosis

Osmosis – diffusion of water – diffusion of water across the membraneacross the membrane

• Passive process involving no expenditure Passive process involving no expenditure of energyof energy

• Water solutions on each side of the Water solutions on each side of the membranemembrane

• High water concentration outside and High water concentration outside and Low water concentration inside Water Low water concentration inside Water moves in.moves in.

• Free water molecules move across the Free water molecules move across the membranemembrane

• Outside of membrane is hydrophilic so Outside of membrane is hydrophilic so water is attracted to it.water is attracted to it.

OsmosisOsmosis

• Diffusion of waterDiffusion of water across a membraneacross a membrane

• Moves fromMoves from HIGH HIGH water potentialwater potential ( (low low solute) tosolute) to LOW LOW water potentialwater potential (high(high solute)solute)

Diffusion across a membrane

Semipermeable

membrane

Diffusion of HDiffusion of H22O Across A O Across A MembraneMembrane

High H2O potentialLow solute concentration

Low H2O potentialHigh solute concentration

Osmotic PotentialOsmotic Potential

• Three possible conditions in Three possible conditions in terms of water concentrationterms of water concentration–IsotonicIsotonic – same – same

concentration in and out of cellconcentration in and out of cell

–HypotonicHypotonic – less solutes – less solutes outside than in celloutside than in cell

–HypertonicHypertonic – more solutes – more solutes outside than in celloutside than in cell

Isotonic Isotonic SolutionSolution

•A solution in which the A solution in which the concentration of dissolved concentration of dissolved substances outside the cell substances outside the cell is the same as the is the same as the concentration inside the concentration inside the cell.cell.

•Iso=equalIso=equal

Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?The cell is at _______________.equilibrium

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

Does osmosis occur in Does osmosis occur in an isotonic solution?an isotonic solution?

•Water molecules still move Water molecules still move into and out of the cell at into and out of the cell at random, but there is no net random, but there is no net change in concentration of change in concentration of water, therefore, no osmosis water, therefore, no osmosis occurs.occurs.

Isotonic EnvironmentIsotonic Environment

Water still diffuses but it diffuses equally in both directions – a state of equilibrium exists.

•Cells in isotonic solutions Cells in isotonic solutions maintain their normal maintain their normal shape.shape.

•Most solutions injected into Most solutions injected into the body are isotonic so the body are isotonic so that cells are not damaged that cells are not damaged by the loss or gain of water.by the loss or gain of water.

Hypotonic Hypotonic SolutionSolution

•““Hypo”- below (lower)Hypo”- below (lower)•A solution in which the A solution in which the

concentration of concentration of dissolved dissolved substancessubstances outside the cell is outside the cell is lowerlower than the concentration inside the than the concentration inside the cell.cell.

•Solution has lots of water, little Solution has lots of water, little solute relative to the cytoplasmic solute relative to the cytoplasmic solution.solution.

Does osmosis occur in Does osmosis occur in a hypotonic solution?a hypotonic solution?

• Yes, the concentration of water Yes, the concentration of water outside the cell is greater than the outside the cell is greater than the concentration inside the cell.concentration inside the cell.

• When water enters the cell, it When water enters the cell, it swells and its internal pressure swells and its internal pressure increases. If it swells too much it increases. If it swells too much it will bust…termed cytolysis.will bust…termed cytolysis.

Cell in Hypotonic SolutionCell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement?

Hypotonic EnvironmentHypotonic Environment

Cells gain water – Cytolysis may result if gradient is great enough, swell and burst.

Role of Osmosis in PlantsRole of Osmosis in Plants• Turgor pressureTurgor pressure – the fluid – the fluid

pressure exerted by the cytoplasm pressure exerted by the cytoplasm against the cell membrane to help against the cell membrane to help maintain rigidity and support.maintain rigidity and support.

• In plants turgor pressure allows for In plants turgor pressure allows for support against gravity on land. support against gravity on land. Requires a hypotonic environment.Requires a hypotonic environment.

• When turgor pressure is lost the When turgor pressure is lost the plant tissue becomes flaccid and plant tissue becomes flaccid and wilted. (wilted. (PlasmolysisPlasmolysis).).

Hypertonic Hypertonic SolutionSolution

•Hyper – “above”Hyper – “above”•A solution in which the A solution in which the

concentration of dissolved concentration of dissolved substances outside the cell is substances outside the cell is higherhigher than the concentration than the concentration inside the cell.inside the cell.– Solution has little water & lots of Solution has little water & lots of

solutesolute

Will osmosis occur in a Will osmosis occur in a hypertonic solution?hypertonic solution?

•Yes, the concentration of Yes, the concentration of water outside the cell is water outside the cell is less than inside the cell.less than inside the cell.

•Water will leave the cell Water will leave the cell and turgor pressure will and turgor pressure will decrease.decrease.

•The cells in hypertonic The cells in hypertonic solutions tend to shrivel solutions tend to shrivel because of the decrease because of the decrease in pressure.in pressure.

PlasmolysisPlasmolysis

•Loss of water Loss of water from a cell from a cell resulting in a resulting in a drop in drop in turgor turgor pressure.pressure.

•Causes a Causes a plant to wilt.plant to wilt.

Osmsosis and a Osmsosis and a plant cellplant cell

Normal cell Wilted cell Permanently Wilted cell

Cell in Hypertonic Cell in Hypertonic SolutionSolution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

Cells in SolutionsCells in Solutions

Cytolysis

Plasmolysis

Isotonic Solution

NO NET MOVEMENT OF

H2O (equal amounts entering

& leaving)

Hypotonic Solution

CYTOLYSIS

Hypertonic Solution

PLASMOLYSIS

Cytolysis & PlasmolysisCytolysis & Plasmolysis

Cytolysis Plasmolysis

Osmosis in Red Blood CellsOsmosis in Red Blood Cells

IsotonicIsotonic Hypotonic

Hypertonic

Three Forms of Transport Across the MembraneThree Forms of Transport Across the Membrane

Passive Passive TransportTransport

Simple DiffusionSimple Diffusion

Doesn’tDoesn’t require require energyenergy

Moves Moves high to lowhigh to low concentrationconcentration Example: Example: OxygenOxygen or or waterwater diffusing into a diffusing into a cell and cell and carbon carbon dioxidedioxide diffusing out diffusing out.

Passive Passive TransportTransport

Facilitated diffusion

Doesn’t require energy

Uses transport proteins to move high to low concentrationExamples: Examples: GlucoseGlucose or or amino acidsamino acids moving moving from blood into a from blood into a cell.cell.

Proteins Are Critical to Proteins Are Critical to Membrane FunctionMembrane Function

Types of Transport ProteinsTypes of Transport Proteins• Channel proteinsChannel proteins are are

embedded in the cell embedded in the cell membrane & have a membrane & have a porepore for for materials to crossmaterials to cross

• Carrier proteinsCarrier proteins can can change change shapeshape to move material from to move material from one side of the membrane to one side of the membrane to the otherthe other

Facilitated DiffusionFacilitated Diffusion

Molecules will randomly move Molecules will randomly move through thethrough the porespores inin Channel Channel ProteinsProteins..

Facilitated Facilitated Diffusion Diffusion Passive Passive

TransportTransport

Facilitated DiffusionFacilitated Diffusion

• SomeSome Carrier Carrier proteinsproteins do not do not extend through extend through the membrane.the membrane.

• They They bond and bond and drag moleculesdrag molecules through the lipid through the lipid bilayer and release bilayer and release them on the them on the opposite side.opposite side.

Facilitated DiffusionFacilitated Diffusion• Form of carrier Form of carrier

transport which transport which increases the rate at increases the rate at which certain molecules which certain molecules pass through the pass through the membrane without the membrane without the expenditure of energy.expenditure of energy.

• Works primarily by Works primarily by changing the size of changing the size of openings in the openings in the membrane.membrane.

• May work to move May work to move molecules in either molecules in either direction (in or out).direction (in or out).

Gated ChannelsGated ChannelsPassive TransportPassive Transport

• A protein controlled passage that permits the A protein controlled passage that permits the cell membrane to be permeable as needed.cell membrane to be permeable as needed.

• Some are permanently open, others open and Some are permanently open, others open and close in response to environmental stimuli.close in response to environmental stimuli.

Gated Gated ChannelsChannelsPassive TransportPassive Transport

Voltage Sensitive Channels These respond to changes in the electrical potential

Active Transport

Requires energy or ATP

Moves materials from LOW to HIGH concentration

AGAINST concentration gradient

Active Active transporttransport

Examples: Examples: PumpingPumping NaNa++ ((sodium ions) out sodium ions) out andand KK++ (potassium (potassium ions) inions) in againstagainst strong strong concentration concentration gradientsgradients..

CalledCalled Na+-K+ PumpNa+-K+ Pump

Carrier TransportCarrier TransportActive TransportActive Transport

The use of special proteins The use of special proteins called carrier molecules called carrier molecules

((permeasespermeases) to move solute ) to move solute molecules across the molecules across the

membrane.membrane.

Carrier MoleculesCarrier Molecules

Chemical Receptors Respond to the presence of specific molecules such as hormones.

Carrier transportCarrier transport

May be either passive or active

Active TransportActive Transport

• Na – K pumpNa – K pump

Active TransportActive Transport• Na – K pumpNa – K pump

Endocytosis and Endocytosis and ExocytosisExocytosis

The The movement of large movement of large particlesparticles (not molecules) (not molecules)

into or out of the cell into or out of the cell without passing through the without passing through the

membrane.membrane.

Moving the “Big Moving the “Big Stuff”Stuff”Large molecules move materials into the Large molecules move materials into the

cell by one ofcell by one of three forms of endocytosisthree forms of endocytosis.

EndocytosisEndocytosis

• The engulfing of large macromolecular The engulfing of large macromolecular particles at the membrane by surrounding particles at the membrane by surrounding them with membrane, forming a vesicle.them with membrane, forming a vesicle.

Two Forms of EndocytosisTwo Forms of Endocytosis

• PhagocytosisPhagocytosis• Engulfing of Engulfing of solidssolids

or food at the or food at the surface of the cell.surface of the cell.

• Sometimes whole Sometimes whole microorganisms microorganisms may be engulfed to may be engulfed to be digested within be digested within the cytoplasmthe cytoplasm

• PinocytosisPinocytosis• Engulfing of Engulfing of liquidsliquids

or solutes at the or solutes at the surface of the cell, surface of the cell, primarily for storage.primarily for storage.

PinocytosisPinocytosis

MostMost commoncommon form of endocytosisform of endocytosis. Takes inTakes in dissolveddissolved molecules as a molecules as a vesiclevesicle.

PinocytosisPinocytosis

• Cell forms anCell forms an invaginationinvagination

• MaterialsMaterials dissolve in dissolve in waterwater to be to be brought into brought into cellcell

• CalledCalled “Cell “Cell Drinking”Drinking”

Example of Example of PinocytosisPinocytosispinocytic vesicles forming mature transport vesicle

Transport across a capillary cell (blue).

Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

SomeSome integral proteinsintegral proteins havehave receptorsreceptors on their surface to on their surface to recognize & take inrecognize & take in hormones, hormones, cholesterolcholesterol, etc., etc.

Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis

Endocytosis – Phagocytosis Endocytosis – Phagocytosis

Used toUsed to engulf large particlesengulf large particles such such asas food,food, bacteriabacteria, etc. into vesicles, etc. into vesicles

CalledCalled “Cell Eating”“Cell Eating”

Phagocytosis About to OccurPhagocytosis About to Occur

PhagocytoPhagocytosissis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

ExocytosisExocytosis• The opposite of endocytosis is The opposite of endocytosis is

exocytosis. Large molecules that are exocytosis. Large molecules that are manufactured in the cell are released manufactured in the cell are released through the cell membranethrough the cell membrane..

• The process of ridding the cell of the The process of ridding the cell of the contents of vacuoles, may consist of contents of vacuoles, may consist of digested wastes or cellular products. digested wastes or cellular products.

Moving the “Big Stuff”Moving the “Big Stuff”

Molecules are moved out of the cell by Molecules are moved out of the cell by vesicles that fuse with the plasma vesicles that fuse with the plasma membrane.membrane.

ExocytosExocytosisis-

moving things out.

This is how many hormones are secreted This is how many hormones are secreted and how nerve cells communicate with and how nerve cells communicate with one anotherone another.

ExocytosisExocytosisExocytic Exocytic vesicle vesicle immediately immediately after fusion after fusion with plasma with plasma membrane.membrane.

AnimationAnimation

•Endocytosis and Exocytosis

Exocytosis:Exocytosis:Golgi Apparatus and excretion Golgi Apparatus and excretion

by glands.by glands.

T-H-ET-H-E E-N-E-N-

DD