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2010 Pearson Education, Inc.
Lectures by Chris C. Romero, updated by Edward J. Zalisko
PowerPoint
Lectures forCampbell Essential Biology, Fourth EditionEric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third EditionEric Simon, Jane Reece, and Jean Dickey
Chapter 50
The Working Cell
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Biology and Society:Natural Nanotechnology
Cells control their chemical environment using Energy Enzymes
The plasma membrane
Cell-based nanotechnology may be used to powermicroscopic robots.
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Figure 5.00
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SOME BASIC ENERGY CONCEPTS
Energy makes the world go around. But what is energy?
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Conservation of Energy
Energy is defined as the capacity to perform work.
Kinetic energy is the energy of motion. Potential energy is stored energy.
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Climbing the stepsconverts kineticenergy of musclemovement topotential energy.
On the platform,the diver has morepotential energy.
Diving convertspotential energyto kinetic energy.
In the water, thediver has lesspotential energy.
Figure 5.1
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Machines and organisms can transform kineticenergy to potential energy and vice versa.
In all such energy transformations, total energy isconserved.
Energy cannot be created or destroyed.
This is the principle ofconservation of energy.
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Entropy
Every energy conversion releases some randomizedenergy in the form of heat.
Heat is a
Type of kinetic energy
Product of all energy conversions
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Scientists use the term entropy as a measure ofdisorder, or randomness.
All energy conversions increase the entropy of theuniverse.
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Chemical Energy
Molecules store varying amounts of potential energyin the arrangement of their atoms.
Organic compounds are relatively rich in suchchemical energy.
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Living cells and automobile engines use the samebasic process to make chemical energy do work.
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Fuel rich inchemicalenergy
Energy conversionWaste productspoor in chemicalenergy
Gasoline
Oxygen
Carbon dioxide
Water
Energy conversion in a car
Energy for cellular work
Energy conversion in a cell
Heatenergy
Heatenergy
Carbon dioxide
Water
Food
Oxygen
Combustion
Cellularrespiration
Kinetic energyof movement
ATP
Figure 5.2
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Cellular respiration is the energy-releasing chemicalbreakdown of fuel molecules that provides energy
for cells to do work. Humans convert about 40% of the energy in food to
useful work, such as the contraction of muscles.
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Food Calories
A calorieis the amount of energy that raises thetemperature of one gram of water by 1 degree
Celsius. Food Calories are kilocalories, equal to 1,000
calories.
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(a) Food Calories (kilocalories) invarious foods
(b) Food Calories (kilocalories) weburn in various activities
CheeseburgerSpaghetti with sauce (1 cup)
Pizza with pepperoni (1 slice)
Peanuts (1 ounce)
Apple
Bean burrito
Fried chicken (drumstick)
Garden salad (2 cups)
Popcorn (plain, 1 cup)
Broccoli (1 cup)
Baked potato (plain, withskin)
FoodCalories
Food
295
241
220
193
181
166
81
56
189
31
25
Activity Food Calories consumed perhour by a 150-pound person*
979
510
490
408
204
73
61
245
28
Running (7min/mi)
Sitting (writing)
Driving a car
Playing the piano
Dancing (slow)
Walking (3 mph)
Bicycling (10 mph)
Swimming (2 mph)
Dancing (fast)
*Not including energy necessary for basic functions, such
as breathing and heartbeat
Figure 5.3
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2010 Pearson Education, Inc.(a) Food Calories (kilocalories) in various foods
Cheeseburge
rSpaghetti with sauce (1 cup)
Pizza with pepperoni (1 slice)
Peanuts (1 ounce)
Apple
Beanburrito
Fried chicken (drumstick)
Garden salad (2 cups)
Popcorn (plain, 1cup)Broccoli (1 cup)
Baked potato (plain, withskin)
FoodCalories
Food
295
241
220
193
181
166
81
56
189
31
25
Figure 5.3a
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2010 Pearson Education, Inc.(b) Food Calories (kilocalories) we burn in various activities
Activity
Food Calories consumed perhour by a 150-poundperson*
979
510490
408
204
73
61
245
28
Running (7min/mi)
Sitting(writing)
Driving a car
Playing thepiano
Dancing(slow)
Walking (3mph)
Bicycling (10mph)Swimming (2 mph)
Dancing (fast)
*Not including energy necessary for basic functions,such as breathing and heartbeat
Figure 5.3b
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The energy of calories in food is burned off by manyactivities.
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ATP AND CELLULAR WORK
Chemical energy is
Released by the breakdown of organic molecules
during cellular respiration
Used to generate molecules of ATP
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ATP
Acts like an energy shuttle
Stores energy obtained from food
Releases it later as needed
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The Structure of ATP
ATP (adenosine triphosphate)
Consists of adenosine plus a tail of three phosphate
groups
Is broken down to ADP and a phosphate group,releasing energy
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Triphosphate Diphosphate
Adenosine Adenosine
Energy
ATP ADP
P P P P P P
Phosphate(transferred to
another molecule)
Figure 5.4
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Phosphate Transfer
ATP energizes other molecules by transferringphosphate groups.
This energy helps cells perform
Mechanical work
Transport work
Chemical work
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ATP
ATP
ATP
ADP
ADP
ADP
P
P
P
ADP P
P P
P
PX X Y
Y
(a) Motor protein performing mechanical work
(b) Transport protein performing transport work
(c) Chemical reactants performing chemical work
Solute
Solutetransported
Protein moved
Product madeReactants
Transportprotein
Motorprotein
Figure 5.5
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ATP ADP PADP P
(a) Motor protein performing mechanical workProtein moved
Motorprotein
Figure 5.5a
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ATP ADP P
P P
(b) Transport protein performing transport work
Solute
Solutetransported
Transportprotein
Figure 5.5b
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ATP ADP P
P
PX X Y
Y
(c) Chemical reactants performing chemical work
Product madeReactants
Figure 5.5c
Th ATP C l
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The ATP Cycle
Cellular work spends ATP.
ATP is recycled from ADP and a phosphate group
through cellular respiration.
A working muscle cell spends and recycles about 10million ATP molecules per second.
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Cellular respiration:chemical energy
harvested from
fuel molecules
Energy for
cellular work
ATP
ADPP
Figure 5.6
ENZYMES
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ENZYMES
Metabolism is the total of all chemical reactions inan organism.
Most metabolic reactions require the assistance ofenzymes, proteins that speed up chemicalreactions.
A ti ti E
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Activation Energy
Activation energy
Activates the reactants
Triggers a chemical reaction
Enzymes lower the activation energy for chemicalreactions.
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(a) Without enzyme (b) With enzyme
Reactant Reactant
Products Products
Activationenergy barrier Activation
energy barrierreduced byenzyme
Enzyme
Energylevel
Energyle
vel
Figure 5.7
Activation
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Reactant
Products
Activationenergy barrier
Energylevel
Figure 5.7a
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Reactant
Products
Activationenergy barrierreduced byenzyme
Enzyme
Energy
leve
l
Figure 5.7b
The Process of Science:
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The Process of Science:Can Enzymes Be Engineered?
Observation: Genetic sequences suggest thatmany of our genes were formed through a type ofmolecular evolution.
Question: Can laboratory methods form newenzymes through artificial selection?
Hypothesis: An artificial process could modify thegene that codes for lactase into a new gene with anew function.
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Experiment: Many copies of the lactase gene wererandomly mutated and tested for new activities.
Results: Directed evolution produced a newenzyme with a novel function.
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Gene for lactase
Mutated genes(mutations shown in orange)
Mutated genes screenedby testing new enzymes
Gene duplicated andmutated at random
Genes coding for enzymesthat show new activity
Genes coding for enzymesthat do notshow new activity
Genes duplicated andmutated at random
Mutated genesscreened
by testing newenzymes
After seven rounds, somegenes code for enzymes that canefficiently perform new activity.
Ribbon model showing the polypeptidechains of the enzyme lactase
Figure 5.8
Gene for lactase
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Gene for lactase
Mutated genes(mutations shown in orange)
Mutated genes screenedby testing new enzymes
Gene duplicated andmutated at random
Genes coding for enzymesthat show new activity
Genes coding for enzymesthat do notshow new activity
Genes duplicated and
mutated at random
Mutated genesscreened
by testing new enzymes
After seven rounds, somegenes code for enzymes that can
efficiently perform new activity. Figure 5.8a
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2010 Pearson Education, Inc. Figure 5.8b
Ribbon model showing the polypeptidechains of the enzyme lactase
Induced Fit
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Induced Fit
Every enzyme is very selective, catalyzing a specificreaction.
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Each enzyme recognizes a substrate, a specificreactant molecule.
The active site fits to the substrate, and the enzymechanges shape slightly.
This interaction is called induced fit.
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Enzymes can function over and over again, a keycharacteristic of enzymes.
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Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
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Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Substrate (sucrose)
Substrate bindsto the enzyme.
Figure 5.9-2
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Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Substrate (sucrose)
Substrate bindsto the enzyme.
The enzymecatalyzes thechemical reaction.
H2O
Figure 5.9-3
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Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Substrate (sucrose)
Substrate bindsto the enzyme.
The enzymecatalyzes thechemical reaction.
H2O
Fructose
Glucose
The productsare released.
Figure 5.9-4
Enzyme Inhibitors
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Enzyme Inhibitors
Enzyme inhibitors can prevent metabolicreactions by binding to the active site.
(a) Enzyme and substrate Substrate
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(a) Enzyme and substratebinding normally
(b) Enzyme inhibition bya substrate imposter
(c) Enzyme inhibition bya molecule that causesthe active site to changeshape
Substrate
Substrate
Active site
Active site
Active site
Inhibitor
Inhibitor
Enzyme
Enzyme
Enzym
e Figure 5.10
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(a) Enzyme and substrate binding normally
Substrate
Enzyme
Activesite
Figure 5.10a
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(b) Enzyme inhibition by a substrate imposter
Substrate
Active site
Inhibitor
Enzyme
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(c) Enzyme inhibition by a molecule thatcauses the active site to change shape
Substrate
Active site
Inhibitor
Enzyme
Figure 5.10c
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Other enzyme inhibitors
Bind at a remote site
Change the enzymes shape
Prevent the enzyme from binding to its substrate
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Some products of a reaction may inhibit the enzymerequired for its production.
This is called feedback regulation.
It prevents the cell from wasting resources.
Many antibiotics work by inhibiting enzymes ofdisease-causing bacteria.
MEMBRANE FUNCTION
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MEMBRANE FUNCTION
Working cells must control the flow of materials toand from the environment.
Membrane proteins perform many functions.
Transport proteins
Are located in membranes
Regulate the passage of materials into and out of thecell
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Cellsignaling
Attachment tothe cytoskeleton
and extracellularmatrix
Enzymatic activity
Cytoskeleton
Cytoplasm
Cytoplasm
Transport
Fibers of
extracellularmatrix
Intercellularjoining
Cell-cellrecognition
Figure 5.11
Passive Transport: Diffusion across Membranes
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Passive Transport: Diffusion across Membranes
Molecules contain heat energy that causes them tovibrate and wander randomly.
Diffusion is the tendency for molecules of anysubstance to spread out into the available space.
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Passive transport is the diffusion of a substanceacross a membrane without the input of energy.
Diffusion is an example of passive transport.
Substances diffuse down their concentrationgradient, a region in which the substancesdensity changes.
Molecules of dye Membrane
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(a) Passive transport of one type of molecule
(b) Passive transport of two types of molecules
Net diffusion Net diffusion Equilibrium
Net diffusion Net diffusion Equilibrium
Net diffusion Net diffusion Equilibrium
Figure 5.12
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Molecules of dye Membrane
(a) Passive transport of one type of molecule
Net diffusion Net diffusion Equilibrium
Figure 5.12a
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(b) Passive transport of two types of molecules
Netdiffusion
Netdiffusion
Equilibrium
Netdiffusion Netdiffusion Equilibrium
Figure 5.12b
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Some substances do not cross membranesspontaneously.
These substances can be transported via facilitateddiffusion.
Specific transport proteins act as selective corridors.
No energy input is needed.
Osmosis and Water Balance
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The diffusion of water across a selectivelypermeable membrane is osmosis.
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Hypotonic solution Hypertonic
solution
Sugarmolecule
Selectively
permeablemembrane
Osmosis
Figure 5.13-1
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Hypotonic solution Hypertonic
solution
Sugarmolecule
Selectively
permeablemembrane
Osmosis
Isotonic solutions
Osmosis
Figure 5.13-2
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A hypertonic solution has a higher concentration ofsolute.
A hypotonic solution has a lower concentration ofsolute.
An isotonic solution has an equal concentration ofsolute.
Water Balance in Animal Cells
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Osmoregulation is the control of water balancewithin a cell or organism.
Most animal cells require an isotonic environment.
Water Balance in Plant Cells
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Plant have rigid cell walls.
Plant cells require a hypotonic environment, which
keeps these walled cells turgid.
Animal cell
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Plant cell
Normal
Flaccid (wilts)
Lysing
Turgid
Shriveled
Shriveled
Plasmamembrane
H2OH2O H2O H2O
H2OH2OH2O H2O
(a) Isotonic
solution
(b) Hypotonic
solution
(c) Hypertonic
solution Figure 5.14
Animal cell
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Plant cell
Normal
Flaccid (wilts)
H2OH2O
H2O H2O
(a) Isotonic
solution Figure 5.14a
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Lysing
Turgid
H2O
H2O
(b) Hypotonicsolution
Figure 5.14b
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Shriveled
Shriveled
Plasmamembrane
H2O
H2O
(c) Hypertonicsolution
Figure 5.14c
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As a plant cell loses water,
It shrivels.
Its plasma membrane may pull away from the cell wallin the process ofplasmolysis, which usually killsthe cell.
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2010 Pearson Education, Inc. Figure 5.15
Active Transport: The Pumping of MoleculesA M b
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Across Membranes
Active transport requires energy to move
molecules across a membrane.
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Lower solute concentration
Higher soluteconcentration
ATP
Solute
Figure 5.16-1
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Lower solute concentration
Higher soluteconcentration
ATP
Solute
Figure 5.16-2
Exocytosis and Endocytosis: Traffic of LargeM l l
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Molecules
Exocytosis is the secretion of large molecules
within vesicles.
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Outside of cell
Cytoplasm
Plasmamembrane
Figure 5.17
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Endocytosis takes material into a cell withinvesicles that bud inward from the plasma
membrane.
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There are three types of endocytosis:
Phagocytosis (cellular eating); a cell engulfs a
particle and packages it within a food vacuole Pinocytosis (cellular drinking); a cell gulps
droplets of fluid by forming tiny vesicles
Receptor-mediated endocytosis; a cell takes invery specific molecules
The Role of Membranes in Cell Signaling
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The plasma membrane helps convey signalsbetween
Cells Cells and their environment
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Receptors on a cell surface trigger signaltransduction pathways that
Relay the signal Convert it to chemical forms that can function within
the cell
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Outside ofcell
Cytoplasm
Reception Transduction
ResponseReceptorprotein
Epinephrine(adrenaline)from adrenalglands
Plasma membrane
Proteins of signal transduction pathway
Hydrolysisof glycogenreleasesglucose forenergy
Figure 5.19
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Outside of cell Cytoplasm
ReceptionTransduction Response
Receptor
protein
Epinephrine(adrenaline)from adrenalglands
Plasma membrane
Proteins of signal transductionpathway
Hydrolysisof glycogenreleasesglucose forenergy
Figure 5.19a
Evolution Connection:The Origin of Membranes
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The Origin of Membranes
Phospholipids
Are key ingredients of membranes
Were probably among the first organic compoundsthat formed before life emerged
Self-assemble into simple membranes
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2010 Pearson Education, Inc. Figure 5.20
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Energy for cellular work
Adenosine
Adenosinediphosphate
Energy fromorganic fuel
Phosphate
ATPcycle
ATP ADP
P P P P P PAdenosine
Adenosine
triphosphate
Figure 5.UN01
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Reactant Reactant
ProductsProducts
Enzyme added
Activ
ationener g
y
Figure 5.UN02
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Passive Transport
(requires no energy)
Active Transport
(requires energy)
Diffusion Facilitated diffusion Osmosis
Higher solute concentration
Lower solute concentration
Higher water concentration(lower solute concentration)
Lower water concentration(higher soluteconcentration)
Solute
Higher soluteconcentration
Lower soluteconcentration
ATP
Solute
Solute
Water
Solute
MEMBRANE TRANSPORT
Figure 5.UN03
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Exocytosis Endocytosis