Powerpoint cell membrane transport

Biology, Cell membranes and Biology, Cell membranes and TransportTransport 11

Transport through cell Transport through cell membranesmembranes

The phospholipid bilayer is a good barrier around cells, The phospholipid bilayer is a good barrier around cells, especially to water soluble molecules. However, for the cell to especially to water soluble molecules. However, for the cell to survive some materials need to be able to enter and leave the survive some materials need to be able to enter and leave the cell.cell.

Mechanisms:Mechanisms:

4.4. DIFFUSIONDIFFUSION

6.6. OSMOSISOSMOSIS

8.8. ACTIVE TRANSPORTACTIVE TRANSPORT

DEFINITIONSDEFINITIONS DIFFUSION: the net movement of molecules from a region of their DIFFUSION: the net movement of molecules from a region of their

higher higher concentration to a region of their concentration to a region of their lowerlower concentration concentration downdown a a concentration gradient, as a result of their random movement.concentration gradient, as a result of their random movement.

OSMOSIS: the diffusion of water molecules from a region of their OSMOSIS: the diffusion of water molecules from a region of their higherhigher concentration (dilute solution) to a region of their concentration (dilute solution) to a region of their lowerlower concentration (concentrated solution), concentration (concentrated solution), through a partially permeable through a partially permeable membrane.membrane.

ACTIVE TRANSPORT: the movement of ions in or out of a cell ACTIVE TRANSPORT: the movement of ions in or out of a cell through the cell membrane, from a region of their through the cell membrane, from a region of their lower lower concentration to a region of their concentration to a region of their higherhigher concentration concentration againstagainst a a concentration gradient, using energy released during respiration. concentration gradient, using energy released during respiration.

Diffusion of liquidsDiffusion of liquids

AS Biology, Cell membranes and AS Biology, Cell membranes and TransportTransport 55

•Diffusion is the net movement of molecules (or Diffusion is the net movement of molecules (or ions) from a region of their high concentration to ions) from a region of their high concentration to a region of their lower concentration.a region of their lower concentration.

The molecules move down a The molecules move down a concentration gradient.concentration gradient.

Molecules have Molecules have kinetic energykinetic energy, which makes them , which makes them move about randomly. move about randomly.

As a result of diffusion molecules reach an As a result of diffusion molecules reach an equilibrium equilibrium where they are evenly spread out.where they are evenly spread out.This is when there is no net movement of molecules This is when there is no net movement of molecules from either side.from either side.

DIFFUSIONDIFFUSIONDiffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural kinetic energy.

Diffusion of BromineDiffusion of Bromine

Diffusion through a membraneDiffusion through a membrane

Cell membrane

Inside cell Outside cell

Cell membrane

diffusion

Cell membrane

EQUILIBRIUM

What determines the rate of diffusion?What determines the rate of diffusion?There 4 factors:There 4 factors:

The steepness of the concentration gradientThe steepness of the concentration gradient. The bigger . The bigger the difference between the two sides of the membrane the difference between the two sides of the membrane the quicker the rate of diffusion. the quicker the rate of diffusion.

TemperatureTemperature. Higher temperatures give molecules or ions . Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so more kinetic energy. Molecules move around faster, so diffusion is faster.diffusion is faster.

The surface areaThe surface area. The greater the surface area the . The greater the surface area the faster the diffusion can take place. This is because the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any more molecules or ions can cross the membrane at any moment.moment.

The type of molecule or ion diffusingThe type of molecule or ion diffusing. Large molecules . Large molecules need more energy to get them to move so they tend to need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the easily than polar molecules because they are soluble in the non polar phospholipid tails.non polar phospholipid tails.

Molecules that diffuse through cell Molecules that diffuse through cell membranesmembranes

OxygenOxygen – Non-polar – Non-polar so diffuses very so diffuses very quickly.quickly.

Carbon dioxideCarbon dioxide – – Polar but very small Polar but very small so diffuses quickly.so diffuses quickly.

WaterWater – Polar but – Polar but also very small so also very small so diffuses quickly.diffuses quickly.

OsmosisOsmosis

‘‘The The diffusiondiffusion of water from an area of water from an area of high concentration of water of high concentration of water molecules (molecules (high water potentialhigh water potential) to ) to an area of low concentration of an area of low concentration of water (water (low water potentiallow water potential) across a ) across a partially permeable membrane.’partially permeable membrane.’

OsmosisOsmosis

Cell membrane partially permeable.

Inside cell Outside cellVERY High conc. of water molecules. High water potential.

VERY Low conc. of water molecules. Low water potential.

Sugar molecule

DILUTE SOLUTIONCONCENTRATED SOLUTION

OsmosisOsmosis

Inside cell Outside cellHigh conc. of water molecules. High water potential.

Low conc. of water molecules. Low water potential.OSMOSIS

OsmosisOsmosis

OSMOSIS

EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water

OSMOSIS IN ANIMAL CELLSOSMOSIS IN ANIMAL CELLSRed blood cellsRed blood cells

OSMOSIS: Slides of red blood OSMOSIS: Slides of red blood cellscells

OSMOSIS IN PLANT CELLSOSMOSIS IN PLANT CELLS

ACTIVE TRANSPORTACTIVE TRANSPORT

ACTIVE TRANSPORT:ACTIVE TRANSPORT:Carrier + energyCarrier + energy

Comparison tableComparison table

EndocytosisEndocytosis is the case when a molecule causes the cell membrane to is the case when a molecule causes the cell membrane to bulge inward, forming a vesicle. bulge inward, forming a vesicle. PhagocytosisPhagocytosis is the type of is the type of

endocytosis where an entire cell is engulfed. Pinocytosis is when the endocytosis where an entire cell is engulfed. Pinocytosis is when the external fluid is engulfed. Receptor-mediated endocytosis occurs when external fluid is engulfed. Receptor-mediated endocytosis occurs when the material to be transported binds to certain specific molecules in the the material to be transported binds to certain specific molecules in the membrane. Examples include the transport of insulin and cholesterol membrane. Examples include the transport of insulin and cholesterol

into animal cells.into animal cells.

Cell Membrane - Function - EndocytosisCell Membrane - Function - Endocytosis The cell membrane can also engulf structures that are much too large to fit through the The cell membrane can also engulf structures that are much too large to fit through the

pores in the membrane proteins this process is known as endocytosis. In this process the pores in the membrane proteins this process is known as endocytosis. In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this

animation an ameba engulfs a food particle.animation an ameba engulfs a food particle.

ExocytosisExocytosis The opposite of endocytosis is exocytosis. Large molecules that are The opposite of endocytosis is exocytosis. Large molecules that are

manufactured in the cell are released through the cell membrane.manufactured in the cell are released through the cell membrane.

Vesicle-mediated transport Vesicle-mediated transport VesiclesVesicles and and vacuolesvacuoles that fuse with the cell membrane may be that fuse with the cell membrane may be

utilized to release or transport chemicals out of the cell or to allow them utilized to release or transport chemicals out of the cell or to allow them to enter a cell. to enter a cell. ExocytosisExocytosis is the term applied when transport is out of is the term applied when transport is out of

the cell.the cell.

Powerpoint cell membrane transport

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