DIFFUSION

DIFFUSIONDiffusion, Osmosis & Active Transport

DIFFUSION DEFINITIONSSOLVENT: a liquid in which a substance is dissolved in (H2O is the UNIVERSAL SOLVENT)

SOLUTE: particles/molecules that are dissolved in the solvent

SOLUTION: the mixture of dissolved particles in the solvent

HYPERTONIC: A highly concentrated solution (high solute) - water molecules will diffuse OUT OF cells in a hypertonic solution

HYPOTONIC: A low concentrated solution (low solute) - water molecules will diffuse INTO cells in hypotonic solution

ISOTONIC: A solution with the same concentration as its surrounding - water molecules will NEITHER move into or out of cells in an isotonic solution (concentration inside and outside the cell are equal)

SEMI-PERMEABLE MEMBRANE: A membrane that separates two areas (eg. Inside/outside of an animal cell) that allows certain substances through but not others. May be selectively permeable according to size, charge, polarity of the substances.

DIFFUSION OVERVIEWDiffusion is the net movement of molecules from a region of high concentration to a region of low concentration

GENERAL DIFFUSION

Diffusion occurs DOWN a concentration gradientIt DOES NOT require energyIt will occur naturally until EQUILIBRIUM is reached (concentration gradient levels out)

The rate of diffusion can be increased via:Increase in concentration gradientIncrease in heatSmaller moleculesMedium the molecules are moving through is a gas

FACILITATED DIFFUSION

Facilitated diffusion is a type of diffusion and works in the same way where the particles move from high to low concentration without the need of any energy

The difference is that facilitated diffusion is across cell membranes and involves assistance by channel proteins or carrier proteins (see right)

Speeds up the rate of diffusion of particular molecules

Substances moved by facilitated diffusion usually cannot diffuse by dissolving in the lipid bilayer

Large polar and non-polar molecules need carrier proteins to move through the membrane (eg. Glucose)ACTIVE TRANSPORTActive transport is the net movement of molecules from a region of low concentration to a region of high concentration

ACTIVE TRANSPORT

Active transport occurs UP/AGAINST a concentration gradient

It is ENERGY REQUIRING

ACTIVE TRANSPORTActive transport often involves channel proteins, carrier proteins or gated channels

It has many important roles to play in cellular processes such asGlucose transport into cellsWaste products out of cellsPotassium/Sodium concentration in nerve cells

The energy required for Active Transport to occur generally comes from ATP generated during Cellular Respiration

OSMOSISOsmosis is the net movement of WATER molecules from a region of high concentration to a region of low concentration across a semi-permeable membrane

OSMOSIS

Osmosis DOES NOT require energy

The more concentrated a solution the more dissolved particles in that solution and therefore the lower the amount of water molecules present

This is the opposite in less concentrated solutions

Therefore water will naturally move across a membrane from a concentrated solution to a dilute solution until equilibrium is reached (See left)

VIDEO OSMOSIS THE BASICS

OSMOTIC PRESSURE: refers to the pressure required to prevent osmosis occurring. Dilute solutions are said to have low osmotic pressure as water is less likely to move into themTHE EFFECT OF OSMOSIS ON ANIMALCELLSAn animal cell will react differently depending on the concentration of the solution it is in

Hypotonic solutions cause water to enter the cell and swell, it can potentially cause the cell to burst

Isotonic solutions cause no change

Hypertonic solutions cause water to move out of the cell and the cell to shrivel

THE EFFECT OF OSMOSIS ON PLANT CELLSPlant cells react in a similar fashion to animal cells when placed in different concentrated mediaThe difference is that plant cells have a cellulose CELL WALL which is not effected by water movementWhen in a hypotonic solution the membrane swells out to the cell wall causing the cell to become TURGID. The cell does not burst.When in a hypertonic solution the cell membrane shrivels away from the cell wall causing the cell to become FLACCID. This process is called PLASMOLYSIS.

DIFFUSION and THE PLASMA MEMBRANE4 methods by which substances (eg. Oxygen, Carbon Dioxide, Water, Amino acids, Fatty acids, Sugars, Vitamins, Mineral ions, hormones etc) move across cell membranes DIFFUSION FACILITATED DIFFUSION OSMOSIS ACTIVE TRANSPORT

The cell membrane is selectively permeable some particles are small enough to fit through pores in the membrane some are helped through large molecules restricted molecules such as water, carbon dioxide, oxygen can pass through easily glucose and ions can move through channels with the assistance of transport proteins

MOVEMENT ACROSS THE PLASMA MEMBRANEPROCESSDEFINITIONPART OF THE CELL INVOLVEDPASSIVE/ ACTIVEEG. OF MATERIAL MOVEDDIFFUSIONMovement of particles from a region of HIGH concentration to a region of LOW concentrationCell Membrane, various organellesPassiveCarbon dioxide, Oxygen, Ethanol, GlycerolFACILITATED DIFFUSIONSame as diffusion but aided by attachment to a specific carrier molecule (IONOPHORE) to pass across a membrane. May involve transport proteins or channel proteinsCell membrane (Carrier proteins, Channel proteins) Passive or ActiveSimple sugars, amino acids, nucleotides, charged ionsOSMOSISNet movement of WATER molecules from a region of HIGH concentration to a LOW concentration through a semi-permeable membraneCell membrane, various organellesPassiveWaterACTIVE TRANSPORTMovement of particles against a concentration gradient from a region of LOW concentration to a region of HIGH concentrationCell membrane (Carrier proteins)ActiveGlucose, some ionsBULK TRANSPORTENDOCYTOSISThe movement of solids or liquids into the cellCell membrane, vesiclesMostly passiveVarious usually large particles such as digestive enzymes, hormones, toxins EXOCYTOSISThe movement of solids or liquids out of the cell (usually via vesicles)Cell membrane, vesiclesMostly passiveVarious usually large particles such as digestive enzymes, hormones, toxinsPINOCYTOSISEndocytosis involving the movement of LIQUIDS into the cellCell membrane, vesiclesMostly passiveLiquidsPHAGOCYTOSISEndocytosis involving the movement of foreign material (mostly solids) into the cell for diigestionCell membrane, vesiclesMostly passiveSolids (usually foreign matter such as bacteriaCELL MEMBRANEFUNCTION: Acts as a SELECTIVE BARRIER between the inside of the cell and external fluid Regulates the transfer of substances into and out of the cell. Supplying nutrients and removing wastes Utilises the processes of DIFFUSION & ACTIVE TRANSPORT Width is usually 7 10 nm

PHOSPHOLIPID BILAYER

HYDROPHOBIC tails form a non-polar hydrophobic interior(VERY INSOLUBLE IN WATER NON-POLAR)

HYDROPHILIC ends face the aqueous medium and are polar(VERY SOLUBLE IN WATER) VIDEO: CRASH COURSE CELL MEMBRANES & TRANSPORTPhospholipid

FLUID MOSAIC MODELThe hydrophobic head tends to dissolve in water and the hydrophobic tails are repelled and force inward forming a PHOSPHOLIPID BILAYER

Phospholipids are capable of sideways movement

Specialised protein molecules are also embedded in a mosaic pattern

Proteins and lipids can flip around in the membrane - protein molecules in the membrane have particular functions and can carry a sugar molecule (GLYCOPROTEIN)

Glycoproteins are often receptors/marker molecules important in cell recognition

The lipid structure gives it the property of being flexible and able to repair itself

Allows it to change shape and for vesicles to be pinched off from them or fuse to it

PERMEABLE SUBSTANCES NON-PERMEABLE SUBSTANCES Small hydrophobic molecules Ions Oxygen, Carbon Dioxide, Nitrogen Na+, H+, K+, Mg+, Cl-, HCO3-

Small uncharged polar molecules Larger uncharged molecules Water, Glycerol, Ethanol Amino acids, Nucleotides, GlucoseMEMBRANE CONTENTSPHOSPHOLIPIDS:The bilayer structure means the non-polar tails act as a barrier for ions and watersoluble substances

CHOLESTEROL:Help regulate the fluidity of the membrane preventing it from becoming too rigid. Mechanical stability so membranes dont break easily

PROTEINS:Transport Proteins: provide hydrophilic channels for ions & polar molecules. Specific for the molecule being transported. Some are enzymes which may catalyse reactions. Can be gated or non-gated. Gated are important for Ca+, Na+ & K+ and muscle/nerve operation

Cell Adhesion Proteins: attach adjacent cells to one another

Hormone Binding Proteins: allow hormones to bind to themand a signal is transmitted to inside of the cell

Cell Recognition Proteins: allows the cell to be recognised asself or foreign and act as markers

GLYCOLIPIDS & GLYCOPROTEINS: Carbohydrate chains are often attached to the lipids and proteins of the outer membrane. These are known as glycolipids and glycoproteins. Project out into watery fluids surrounding the cell where they form hydrogen bonds with water. They help stabilise the membrane structure. Can act as receptor molecules for hormones or neurotransmitters. Are the basis for cell ANTIGENS.

*may be called glycocalyx

CELL MEMBRANEand PROTEINS

Free to share, print, make copies and changes. Get yours at www.boundless.comStructure and Function of Plasma MembranesWhich of the following is a function of plasma membranes?A) Organizing cellular processesB) Regulating transportation of materials in and out of a cellC) Communicating directly with the cell nucleusD) Producing proteins and hormones

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Structure and Function of Plasma MembranesWhich of the following is a function of plasma membranes?A) Organizing cellular processesB) Regulating transportation of materials in and out of a cellC) Communicating directly with the cell nucleusD) Producing proteins and hormones

Free to share, print, make copies and changes. Get yours at www.boundless.comStructure and Function of Plasma MembranesWhich of the following statements best describes the lipid bilayer plasma membrane?A) The interior and exterior surfaces of the membrane are hydrophobic and the middle is hydrophilicB) The interior and exterior surfaces of the membrane are hydrophilic and the middle is hydrophobicC) The interior surface and the middle of the membrane are hydrophobic and the exterior is hydrophilicD) The exterior surface and the middle of the membrane are hydrophobic and the interior is hydrophilic

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Structure and Function of Plasma MembranesWhich of the following statements best describes the lipid bilayer plasma membrane?A) The interior and exterior surfaces of the membrane are hydrophobic and the middle is hydrophilicB) The interior and exterior surfaces of the membrane are hydrophilic and the middle is hydrophobicC) The interior surface and the middle of the membrane are hydrophobic and the exterior is hydrophilicD) The exterior surface and the middle of the membrane are hydrophobic and the interior is hydrophilic

Free to share, print, make copies and changes. Get yours at www.boundless.comStructure and Function of Plasma MembranesWhat does the term 'mosaic' refer to in the fluid mosaic model of the plasma membrane?A) The heterogeneous composition of phospholipids, cholesterol, proteins, and carbohydratesB) The array of colors seen when the plasma membrane is viewed with a microscopeC) That scientists had to put together pieces from various models to make one to fitD) The different sizes of plasma membranes that exist in nature

Free to share, print, make copies and changes. Get yours at www.boundless.comBoundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/

Structure and Function of Plasma MembranesWhat does the term 'mosaic' refer to in the fluid mosaic model of the plasma membrane?A) The heterogeneous composition of phospholipids, cholesterol, proteins, and carbohydratesB) The array of colors seen when the plasma membrane is viewed with a microscopeC) That scientists had to put together pieces from various models to make one to fitD) The different sizes of plasma membranes that exist in nature

Free to share, print, make copies and changes. Get yours at www.boundless.comStructure and Function of Plasma MembranesWhat role does cholesterol play in plasma membrane fluidity?A) Cholesterol has a detrimental role in membrane fluidity.B) Cholesterol extends the range of temperature in which the membrane is fluid and functional.C) Cholesterol acts like a magnet pulling proteins around the membrane.D) Cholesterol forces out the unsaturated fatty acids that 'kink' from the membrane.

Free to share, print, make copies and changes. Get yours at www.boundless.comBoundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/

Structure and Function of Plasma MembranesWhat role does cholesterol play in plasma membrane fluidity?A) Cholesterol has a detrimental role in membrane fluidity.B) Cholesterol extends the range of temperature in which the membrane is fluid and functional.C) Cholesterol acts like a magnet pulling proteins around the membrane.D) Cholesterol forces out the unsaturated fatty acids that 'kink' from the membrane.