Diffusion, Osmosis & Active Transport

 SOLVENT: 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 is the net movement of molecules from a region of high concentration to a region of low concentration Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration

Diffusion occurs DOWN a concentration gradient It DOES NOT require energy It will occur naturally until EQUILIBRIUM is reached (concentration gradient levels out) The rate of diffusion can be increased via:  Increase in concentration gradient  Increase in heat  Smaller molecules  Medium the molecules are moving through is a gas

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

Active transport occurs UP/AGAINST a concentration gradient It is ENERGY REQUIRING

Active transport often involves channel proteins, carrier proteins or gated channels It has many important roles to play in cellular processes such as  Glucose transport into cells  Waste products out of cells  Potassium/Sodium concentration in nerve cells The energy required for Active Transport to occur generally comes from ATP generated during Cellular Respiration

Osmosis 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 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 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 them

An 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

Plant cells react in a similar fashion to animal cells when placed in different concentrated media CELL WALL The difference is that plant cells have a cellulose CELL WALL which is not effected by water movement TURGID When in a hypotonic solution the membrane swells out to the cell wall causing the cell to become TURGID. The cell does not burst. FLACCID. PLASMOLYSIS. 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.

4 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

PROCESSDEFINITIONPART OF THE CELL INVOLVED PASSIVE/ ACTIVE EG. OF MATERIAL MOVED DIFFUSION Movement of particles from a region of HIGH concentration to a region of LOW concentration Cell Membrane, various organelles PassiveCarbon dioxide, Oxygen, Ethanol, Glycerol FACILITATED DIFFUSION Same as diffusion but aided by attachment to a specific carrier molecule (IONOPHORE) to pass across a membrane. May involve transport proteins or channel proteins Cell membrane (Carrier proteins, Channel proteins) Passive or Active Simple sugars, amino acids, nucleotides, charged ions OSMOSIS Net movement of WATER molecules from a region of HIGH concentration to a LOW concentration through a semi-permeable membrane Cell membrane, various organelles PassiveWater ACTIVE TRANSPORT Movement of particles against a concentration gradient from a region of LOW concentration to a region of HIGH concentration Cell membrane (Carrier proteins) ActiveGlucose, some ions BULK TRANSPORT ENDOCYTOSIS The movement of solids or liquids into the cellCell membrane, vesiclesMostly passiveVarious usually large particles such as digestive enzymes, hormones, toxins EXOCYTOSIS The movement of solids or liquids out of the cell (usually via vesicles) Cell membrane, vesiclesMostly passiveVarious usually large particles such as digestive enzymes, hormones, toxins PINOCYTOSIS Endocytosis involving the movement of LIQUIDS into the cell Cell membrane, vesiclesMostly passiveLiquids PHAGOCYTOSIS Endocytosis involving the movement of foreign material (mostly solids) into the cell for diigestion Cell membrane, vesiclesMostly passiveSolids (usually foreign matter such as bacteria

FUNCTION:  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 & TRANSPORT

The 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 -, HCO 3 - Small uncharged polar molecules Larger uncharged molecules  Water, Glycerol, Ethanol  Amino acids, Nucleotides, Glucose

PHOSPHOLIPIDS: 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 don’t 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 them and a signal is transmitted to inside of the cell Cell Recognition Proteins: allows the cell to be recognised as ‘self’ 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 MEMBRANE and PROTEINS

Free to share, print, make copies and changes. Get yours at Structure and Function of Plasma Membranes Which of the following is a function of plasma membranes? A) Organizing cellular processes B) Regulating transportation of materials in and out of a cell C) Communicating directly with the cell nucleus D) Producing proteins and hormones

Free to share, print, make copies and changes. Get yours at Boundless - LO. "Boundless." CC BY-SA BY-SA 3.0http:// Structure and Function of Plasma Membranes Which of the following is a function of plasma membranes? A) Organizing cellular processes B) Regulating transportation of materials in and out of a cell C) Communicating directly with the cell nucleus D) Producing proteins and hormones

Free to share, print, make copies and changes. Get yours at Structure and Function of Plasma Membranes Which 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 hydrophilic B) The interior and exterior surfaces of the membrane are hydrophilic and the middle is hydrophobic C) The interior surface and the middle of the membrane are hydrophobic and the exterior is hydrophilic D) 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 Boundless - LO. "Boundless." CC BY-SA BY-SA 3.0http:// Structure and Function of Plasma Membranes Which 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 hydrophilic B) The interior and exterior surfaces of the membrane are hydrophilic and the middle is hydrophobic C) The interior surface and the middle of the membrane are hydrophobic and the exterior is hydrophilic D) 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 Structure and Function of Plasma Membranes What does the term 'mosaic' refer to in the fluid mosaic model of the plasma membrane? A) The heterogeneous composition of phospholipids, cholesterol, proteins, and carbohydrates B) The array of colors seen when the plasma membrane is viewed with a microscope C) That scientists had to put together pieces from various models to make one to fit D) The different sizes of plasma membranes that exist in nature

Free to share, print, make copies and changes. Get yours at Boundless - LO. "Boundless." CC BY-SA BY-SA 3.0http:// Structure and Function of Plasma Membranes What does the term 'mosaic' refer to in the fluid mosaic model of the plasma membrane? A) The heterogeneous composition of phospholipids, cholesterol, proteins, and carbohydrates B) The array of colors seen when the plasma membrane is viewed with a microscope C) That scientists had to put together pieces from various models to make one to fit D) The different sizes of plasma membranes that exist in nature

Free to share, print, make copies and changes. Get yours at Structure and Function of Plasma Membranes What 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 Boundless - LO. "Boundless." CC BY-SA BY-SA 3.0http:// Structure and Function of Plasma Membranes What 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.