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THE WORKING CELL. Why do living organisms need energy?. To be able to carry out life’s functions such as growth, repair, movement, transport. Living cells need a constant supply of energy for breaking and making molecules such as proteins. What Can Cells Do with Energy?.

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Why do living organisms need energy l.jpg
Why do living organisms need energy?

  • To be able to carry out life’s functions such as growth, repair, movement, transport.

  • Living cells need a constant supply of energy for breaking and making molecules such as proteins.


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What Can Cells Do with Energy?

  • Every time you acquire energy you can use it to do an energy requiring action

  • Cells do chemical work

  • Cells can do mechanical work


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Figure 5.1A–C


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Kinetic and Potential energy

  • Potential is stored energy.

  • Ex: A resting bird

  • Kinetic is the energy of motion

  • Ex: a bird in flight


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Different forms of Energy

  • Forms of energy

    • Electrical

    • Mechanical

    • Chemical

    • Light

    • Heat


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What is energy?

  • The capacity to do work, to cause change, to make things happen. We can measure it and experience its effects but we can’t see it.

  • What are the different forms of energy?

  • Two broad categories are

  • Potential energy stored, waiting to be released

  • Kinetic energy is energy associated with motion

  • Chemical energy (type of potential energy) is found in the chemical bonds of molecules such as a lump of coal, a steak, electricity, light.


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How do we measure energy?

  • Calorie

Usually in the form of HEAT because all forms ofenergycan be converted to heat.

The Unit is : Calorie or Kilocalories (1000 calories).

Unit of work is: Joule or Kilojoule


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How do organisms obtain energy?

  • Green plants from the sun. Autotrophs

  • Animals, by eating the green plants or other animals. Heterotrophs

  • Where is the energy in food?

  • In the chemical bonds of its molecules.

  • The energy in food is in the electrons spinning around its atoms. The cells strip these electrons and use them to power their lives.


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Energy can be converted from one form to another.

  • As the boy climbs the ladder to the top of the slide he is converting his kinetic energy to potential energy.

  • As he slides down, the potential energy is converted back to kinetic energy.

  • It was the potential energy in the food he had eaten earlier that provided the energy that permitted him to climb up.


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Energy Flows in one direction

  • All energy for life comes from the sun

  • Producers trap energy from the sun and convert it into chemical bond energy

    Consumers are those that eat the producers

  • Allorganisms use the energy stored in the bonds of organic compounds to do work


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Materials are recycled

  • While energy flows in one direction materials are used over and over again


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What laws govern energy transformations?

  • All living things obey the laws ofthermodynamics. Thermo means heat

  • Thermodynamics is the study of heat transfers.


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Thermodynamics

  • Thermodynamics is the study of energy transformations.All energy is transformed to heat energy.

    A closed systemis isolated from its surroundings.

    • Organisms are open systems.

      • They absorb energy - light or chemical energy in organic molecules - and release heat and metabolic waste products into the environment.

      • In an open system energy can be transferred between the system and surroundings.


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First Law of Thermodynamics

  • The total amount of energy in the universe does not change, remains constant. We can say that energy cannot be created nor destroyed, it can only be transformed from one form to another. This is the “Law of Conservation of Energy”

  • Energy can undergo conversions from one form to another.

    The total energy in a closed system remains constant. Living organisms are open systems. Organisms can only convert energy from one form to another.


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Second Law of Thermodynamics

  • During every energy transformations some energy is lost as heat.No energy conversion is 100 percent efficient.

  • The total amount of energy flows from high-energy forms to lower energy forms. Energy transfers increase disorder.

  • Example: as the chemical energy in gasoline is transformed into kinetic energy of motion in you car, heat is released.


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  • The Second Law of Thermodynamics

    • The second law of thermodynamics

      • States that energy transformations increase disorder or entropy, and some energy is lost as heat

Heat

Chemical reactions

Carbon dioxide

+

Glucose

+

ATP

ATP

water

Oxygen

Energy for cellular work

Figure 5.2B


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Entropy

  • Is the measurement of the degree of disorder in a system

  • The world of life can resist the flow toward maximum entropy only because it is getting more energy from the sun (plants)

  • Animals eat to get energy and fight entropy


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ATP

ATP shuttles chemical energy and drives cellular work

  • ATP powers nearly all forms of cellular work

  • ATP is made in the mitochondria of cells


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Phosphategroups

Adenosine diphosphate

Adenosine Triphosphate

H2O

+

P

Energy

P

P

P

P

P

+

Hydrolysis

Adenine

Ribose

ATP

ADP

  • The energy in an ATP molecule

    • Lies in the bonds between its phosphate groups

Figure 5.4A


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ATP

Phosphorylation

Hydrolysis

Energy fromexergonicreactions

Energy forendergonicreactions

ADP

+

P

  • Cellular work can be sustained

    • Because ATP is a renewable resource that cells regenerate

Figure 5.4C


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Metabolism and energy coupling

  • Cells carry out thousands of chemical reactions

    • The sum of which constitutes cellular metabolism

  • Energy coupling

    • Uses exergonic reactions to fuel endergonic reactions


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Exergonic reactions fuel endergonic reactions

  • Endergonic: Energy input required.

    Ex: photosynthesis

  • Product has more energy than starting substances

  • Exergonic reaction

    Ex: cellular respiration and wood burning

    _____________________________

  • Endergonic= energy IN

  • Exergonic= energy OUT


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Products

Amount of energyrequired

Energy required

Potential energy of molecules

Reactants

Chemical reactions either store or release energy

  • Endergonic reactions

    • Absorb energy and yield products rich in potential energy

Figure 5.3A


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Reactants

Amount of energyreleased

Energy released

Potential energy of molecules

Products

  • Exergonic reactions

    • Release energy and yield products that contain less potential energy than their reactants

Figure 5.3B


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Exergonic reactions

  • Energy is released

  • Products have less energy than starting substance

energy-rich

starting

substance

ENERGY

OUT

products with less energy


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ENZYMES

  • To survive organisms must obtain energy from nutrients in a short time.

  • Chemical reactions to break down a molecule could take along time. For example to break sucrose (table sugar) in a candy bar into glucose and fructose for the body to use could take a very long time. Living cells cannot wait that long. There is a way to speed up reactions without increasing the temperature.

  • What is a catalyst? A catalyst is a chemical that speeds the reaction but is not used up in the reaction.


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What are enzymes?

  • Enzymes are organic proteins that speed up the rate of chemicals reactions without changing the temperature.

  • How do enzymeswork? By lowering the activation energy, which means lowering the amount of energy needed to get a reaction going.


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Chloroplasts and mitochondria make energy available for cellular work

  • Enzymes are central to the processes that make energy available to the cell


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HOW ENZYMES FUNCTION? cellular work

  • Enzymes speed up the cell’s chemical reactions by lowering energy barriers

    In other words enzymes work by lowering the activation energy, which means lowering the amount of energy needed to get a reaction going.


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E cellular workA barrier

Enzyme

Reactants

Products

1

2

  • For a chemical reaction to begin

    • Reactants must absorb some energy, called the energy of activation

Figure 5.5A


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The cellular workInduced-Fit model.

  • The Induced-Fit model. It almost (but not quite) fit precisely in the active site.


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1 cellular work

Enzyme availablewith empty activesite

Substrate binds to enzyme with induced fit

2

4

Products arereleased

3

Substrate is converted to products

  • THIS IS HOW ENZYMES WORK

Active site

Substrate(sucrose)

Enzyme(sucrase)

Glucose

Fructose

H2O

Figure 5.6


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Definitions: cellular work

  • Active site: crevice , groove pocket where the substrate molecule fits and is changed.

  • Substrate: molecule acted upon, changed in some way by the enzyme

  • End product: final result of reaction


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Theory of enzyme action cellular work

  • The Induced-Fit model. It almost (but not quite) fit precisely in the active site.


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ENZYMES ARE HYGHLY SPECIFIC cellular work

  • A specific enzyme catalyzes each cellular reaction.There is a different enzyme for each reaction.

    • Enzymes have unique three-dimensional shapes

      that determine which chemical reactions occur in a cell


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Characteristics of enzymes. cellular work

  • are proteins

  • are reusable

  • reactions are reversible. Work forward and backward

  • highly specific structure that matches the structure of the substrate molecule

  • the ending –“ase” tells you it is an enzyme. Ex: polymerase, amylase, DNAse, sucrase


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  • Factors that affect enzyme action cellular work:

  • A protein (enzyme) gets DENATURED in these conditions.(Denatured means: Its three dimensional SHAPE is disrupted).

  • extreme temperatures

  • pH above 8 or below 6

  • extreme salinity ( high salt concentrations)

  • The cellular environment affects enzyme activity

    • Some enzymes require non -protein cofactors

      • Such as metal ions or organic molecules called coenzymes

      • NAD+, FAD, zinc, some vitamins.


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Chemical factors that control enzymes cellular work

cofactors

Small molecules that help enzymes catalyze reactions.

How?

Usually binds to the active site. Many are vitamins (called coenzymes) and others are inorganic metals such as zinc, iron or copper. All are “enzyme helpers”.


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Enzyme inhibitors block enzyme action cellular work

  • Inhibitors interfere with an enzyme’s activity

  • There are competitive and non-competitive inhibitors


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enzyme inhibitors cellular work

  • How? Certain chemicals can inhibit enzyme activity and it can be irreversible in many cases.

  • These can be competitive and non-competitive

  • Competitive inhibitors are chemicals that resemble the enzymes normal substrate and compete for its active site. They can block the active site from the substrate.

  • Noncompetitive inhibitors are substances that do not enter the enzyme’s active site but bind toanother part of the enzymecausing the enzyme tochange its shape. Many metabolic poisons as well as some antibiotics work this way.


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Active site cellular work

Substrate

Enzyme

Normal binding of substrate

Competitiveinhibitor

Noncompetitiveinhibitor

Enzyme inhibition

  • A competitive inhibitor

    • Takes the place of a substrate in the active site

  • A noncompetitive inhibitor

    • Alters an enzyme’s function by changing its shape

Figure 5.8


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Allosteric regulation cellular work How?

  • Most enzymes have a receptor site on some other part of the enzyme molecule that is not the active site.

  • Allosteric enzymes can change back and forth between an active and an inactive form.

  • When there is an “activator” binding to the allosteric site, the enzyme enters reactions.

  • When there is an “inhibitor” binding to the allosteric site, the enzyme becomes inactive.

  • The activator or inhibitor at the active site changes the shape of the active site.


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  • How is enzyme action controlled? cellular work

  • By a feedback mechanism.

  • This is ALLOSTERIC CONTROL. The molecule binds to the enzyme at a different site changing its shape.


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Web sites to check : cellular work

  • http://programs.northlandcollege.edu/biology/Biology1111/animations/enzyme.html

  • http://resources.ed.gov.hk/biology/english/virtual_lab/flash/enzyme_lab.html



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TRANSPORT ACROSS THE MEMBRANE cellular work

  • Cell membranes are semi-permeable, membranes show “SELECTIVE PERMEABILITY” which means some substances can pass through but others cannot. This is because it is a phospholipid bilayer.

  • The size of a molecule, its concentrationand its electrical charge determine how it passes across.


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Transport across cell membranes cellular work

Passive transport

Diffusion and Osmosis

Active transport

Endocytosis

Exocytosis


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Check these: cellular work

  • http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm

  • http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

  • http://www2.nl.edu/jste/osmosis.htm#Osmosis


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What is “concentration gradient”? cellular work

  • Concentration gradient means that the number of molecules in one area is different than the number in another area

  • A substance moves from a region where it is more concentrated to one one where it is less concentrated - “down” gradient


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How do cell get the nutrients and materials they need, get rid of wastes, controls secretions and maintain its volume?

  • Through a combination of diffusion, facilitated diffusion, osmosis and active transport as well as bulk passage of larger ones as in Endocytosis, Exocytosis and Phagocytosis.


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Passive Transport rid of wastes, controls secretions and maintain its volume?

  • Facilitated Diffusion

    • Flow of solutes through the interior of transport proteins down their concentration gradients

  • Passive transport proteins allow solutes to move both ways. Does not require any energy input

  • Remember transport proteins?

    Embedded in the lipid bilayer they are able to open to both sides and play roles in active and passive transport


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Molecules of dye rid of wastes, controls secretions and maintain its volume?

Membrane

Equilibrium

Equilibrium

  • Passive transport is diffusion across a membrane

    • In passive transport, substances diffuse through membranes without work by the cell

      • Spreading from areas of high concentration to areas of low concentration

Figure 5.14A

Figure 5.14B


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What is diffusion? rid of wastes, controls secretions and maintain its volume?

  • The net movement of molecules down a concentration gradient. This means the movement of solutes from higher to lower concentrations.

  • What drives this movement?

    Brownian movement. The molecules are bumping against each other because they have kinetic energy.

  • The molecules collide at random, the net movement is away from the place with the most collisions (down gradient).


Diffusion l.jpg
Diffusion rid of wastes, controls secretions and maintain its volume?

  • Diffusion is the movement of molecules down its concentration gradient. This means from higher concentration to lower concentration ( from where there are moremolecules to where there are less ).

  • Substances that move across the membrane by simple diffusion are H2O, O2, and CO2


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Solute rid of wastes, controls secretions and maintain its volume?molecule

Transportprotein

  • Transport proteins may facilitate diffusion across membranes

    • Many kinds of molecules

      • Do not diffuse freely across membranes

    • For these molecules, transport proteins

      • Provide passage across membranes through a process called facilitated diffusion

Figure 5.15


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Facilitated diffusion rid of wastes, controls secretions and maintain its volume?

  • Facilitated diffusion involves channels in transport proteins embedded in the cell membrane. It is aided by the concentration gradient BUT NO ENERGY is needed.

  • The molecules lashes on or binds to the binding sites in the transport proteins special channel. This causes the protein to change shape to let it through.

  • Glucose, amino acids and other hydrophilic molecules pass this way.


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Molecules are in constant motion. This random motion is called Brownian movement.

The degree to which molecules are in motion determines their temperature.

Absolute zero is the point at which all molecular movement stops.

What drives this movement?


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Factors Affecting Diffusion Rate called

  • Concentration gradient

    • Steeper gradient, faster diffusion

  • Molecularsize

    • Smaller molecules, faster diffusion

  • Temperature

    • Higher temperature, faster diffusion

  • Electrical or pressure gradients


Equilibrium l.jpg
Equilibrium called

  • Molecules will continue to move until there is an equal concentration on both sides of the membrane or are all evenly distributed in the area.

    It is in dynamic equilibrium when as many molecules pass one way as cross in the other direction.


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OSMOSIS called

Osmosis is a special kind of diffusion involving water.

Osmosis is diffusion of water molecules across a selectively permeable membrane

  • Direction of net flow is determined by water concentration gradient (from where there is more water to where there is less water).

  • Side with the most solute molecules has the lowest water concentration


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OSMOSIS called

Is diffusion of water across a membrane or “movement of water across a selectively permeable membrane following the concentration gradient”.

Water moves into an area of higher solute concentration.

Water moves across a membrane from an area of lower solute concentration to an area of higher solute concentration. This is the same as saying from where there is more water to where there is less water.

SOLUTE: any dissolved substance.

SOLVENT:substance in which the solute is dissolved, in cells usually water.


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Equal called concentrationof solute

Higherconcentrationof solute

Lowerconcentrationof solute

H2O

Solutemolecule

Selectivelypermeablemembrane

Watermolecule

Solute molecule with

cluster of water molecules

Net flow of water

  • Osmosis is the diffusion of water across a membrane

    • In osmosis water travels from a solution of lower solute concentration to one of higher solute concentration

Figure 5.16


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Tonicity called

  • Cells are surrounded by water on both sides of the membrane.

  • We need to consider the solute concentration on both sides of the membrane.

  • Isotonic or isosmotic: When the solute concentration is the same on both sides of the membrane. There is a flow back and forth and it will be balanced.

  • Keep in mind that hyper or hypo refers to the solute concentration


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What is tonicity? called

Tonicity refers to relative solute concentrationof two fluidson either side of the membrane

Hypertonic - have more solutes

Isotonic - have same amount of solutes

Hypotonic - have fewer solutes


Osmosis and tonicity l.jpg
Osmosis and tonicity called

2%

sucrose

10% sucrose

Hypertonic

2% sucrose

Isotonic

Pure water

Hypotonic


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Hypertonic solution called

Hypotonic solution

Isotonic solution

H2O

H2O

H2O

H2O

Animalcell

(3) Shriveled

(2) Lysed

(1) Normal

Plasmamembrane

H2O

H2O

H2O

H2O

Plantcell

(6) Shriveled (plasmolyzed)

(5) Turgid

(4) Flaccid

  • Water balance between cells and their surroundings is crucial to organisms

    • Osmosis causes cells to shrink in hypertonic solutions

      • And swell in hypotonic solutions

    • In isotonic solutions

      • Animal cells are normal, but plant cells are limp


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Imagine that two sugar solutions with different concentrations are separated by a membrane that will allow water to pass through, but not sugar.

  • The hypertonic solution has a higher concentration of solutes but a lower water concentration than the hypotonic solution.

    More of the water molecules in the hypertonic solution are bound up in hydration spheres around the sugar molecules, leaving fewer unbound water molecules.

  • Water molecules will move from the hypotonic solution where they are abundant to the hypertonic solution where they are scarce.


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Active concentrations are separated by a membrane that will allow water to pass through, but not sugar.Transport

  • Net movement of solute is against concentration gradient

  • Transport protein must be activated by using energy (ATP)

  • ATP gives up phosphate to activate protein

    Binding of ATP changes protein shape and affinity for solute


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Transport concentrations are separated by a membrane that will allow water to pass through, but not sugar.protein

P

P

P

Phosphatedetaches

Proteinchanges shape

ATP

Solute

ADP

Transport

1

Solute binding

2

Phosphorylation

3

4

Protein reversion

  • Cells expend energy for active transport

    • Transport proteins can move solutes against a concentration gradient

      • Through active transport, which requires ATP

Figure 5.18


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Passive and active transport concentrations are separated by a membrane that will allow water to pass through, but not sugar.


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Vesicle forming concentrations are separated by a membrane that will allow water to pass through, but not sugar.

  • Membranes may fold inward

    • Enclosing material from the outside (endocytosis)

Figure 5.19B


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Fluid outside cell concentrations are separated by a membrane that will allow water to pass through, but not sugar.

Vesicle

Protein

Cytoplasm

  • Exocytosis and endocytosis transport large molecules

    • To move large molecules or particles through a membrane

      • A vesicle may fuse with the membrane and expel its contents (exocytosis)


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Plasma membrane concentrations are separated by a membrane that will allow water to pass through, but not sugar.

Food being ingested

Pseudopodium of amoeba

Material bound to receptor proteins

PIT

TEM 96,500 

TEM 54,000

Cytoplasm

LM 230

Phagocytosis

Receptor-mediated endocytosis

Pinocytosis

  • Endocytosis can occur in three ways

    • Phagocytosis (cell eating)

    • Pinocytosis (cell drinking)

    • Receptor-mediated endocytosis

Figure 5.19C