B2.1 Membranes and Membrane Transport (2) PDF

B2.1 Membranes and membrane transport B2.1.1 Lipid bilayers as the basis of cell membranes Limit of the cell that contains structure inside. Border between inside and the environment Transport of substance inside and outside the cell. Form by a bilayer of phospholipids and other molecul...

B2.1 Membranes and membrane transport B2.1.1 Lipid bilayers as the basis of cell membranes Limit of the cell that contains structure inside. Border between inside and the environment Transport of substance inside and outside the cell. Form by a bilayer of phospholipids and other molecules. Protection Freeze- fracture electron micrographs B2.1.2 Lipid bilayers as barriers Amphipathetic: Its mean that part of the molecule is attracted to water (hydrophilic phosphate head) and part is not attracted to water ( hydrophobic hydrocarbon tail). Hydrophobic tail has two fatty acid tails composed by hydrocarbon chains. https://www.youtube.com/watch?v=QpcACa39YtA Molecular size also influences membrane permeability. The larger the molecule, the lower the permeability. Fluid mosaic model B2.1.4 Integral and peripheral proteins in membranes Integral:are embedded in the phospholipid bilayer. Peripheral: are attached to the outer surface of the membrane. Glicoproteins: have sugar units attached to the outer surface of the membrane. B2.1.12 Cholesterol Hydrophobic molecule Cholesterol fits between phospholipids in the membrane Restricts the movement of phospholipids molecules, it therefore reduces the fluidity and reduces the permeability of the membrane. Diffusion of ions through the membrane must be restricted. 1.4 Membrane transport Solutes Solvent https://www.youtube.com/watch?v=aubZU0iWtgI  Using energy (ATP) No ATP B2.1.3. Simple diffusion across membrane: is the passive movement of particles from a region of higher concentration to a region of lower concentration, as a result of random movements of particles. http://virtualbiologylab.org/NetWebHTML_FilesJan2016/SemiPermiableModel.html B2.1.6 Facilitated diffusion: substance diffuse through membrane using proteins channels. B2.1.5 Osmosis: is a passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration, across a partially permeable membrane. Osmolarity of a solution is the number of moles of solutes particles per unit volume solution. Branching of roots increase surface area Cytoplasm of Water and minerals ions root cells have phosphate higher solute Osmosis potassium Active transport concentration water nitrate  The incompressibility of water allows transport along hydrostatic pressure gradients. Hydrostatic pressure is pressure in a liquid. The high concentrations of solutes such as sugars in the phloem sieve tubes at the source lead to water uptake by osmosis and high hydrostatic pressure. The low solute concentrations of phloem sieve tubes at the sink lead to exit of water by osmosis and low hydrostatic pressure. There is therefore a pressure gradient that makes sap inside phloem sieve tubes flow from the sources to sinks. https://www.khanacademy.org/science/in-in-class-10-biology/in-in-life-processes/in-in-transportation-in-plants/v/phloem -translocation-life-processes-biology-khan-academy B2.1.7 Active transport: is the movement of substance across membranes using energy from ATP. Structure and function of sodium _ potassium pump in axon Antiporter: sodium and potassium are pumped in opposite directions. ATPasa: is as enzyme responsible of converting ATP in ADP+ P ATP: is the energy necessary to pump the ions Na and K. https://www.youtube.com/watch?v=_bPFKDdWlCg  B2.1.13 Transport using vesicles The fluidity of membranes allows them to move and change shape. Endocytosis: Small pieces of membrane can be pinched of the plasma membrane to create a vesicle containing some material from outside the cell. Exocytosis:Vesicles can also move to the plasma membrane and fuse with it, releasing the contents of the vesicle outside the cell.  Only HL Gated ion channels in neurons Ion channels allow specific ions to pass across a membrane in either direction, resulting in a net movement from the higher to the lower concentration of the ion. This type of membrane transport is facilitated diffusion. Gated ion channels are able to open and close reversibly (on - off) Voltage-gated sodium and potassium channels A nerve impulse involves rapid movements If it rises above −50 mV sodium channels open, of sodium and potassium ions across a allowing sodium ions (Na+) to diffuse in. neuron’s membrane. When it reaches +40 mV, potassium channels Voltages across membranes are due to an open, allowing potassium ions (K+) to diffuse imbalance of positive and negative charges out of the neuron. across the membrane. A negative voltage indicates that there are relatively more positive charges outside the neuron than inside. If the voltage is below −50 mV, sodium and potassium channels remain closed. D2.3 Water Polarity SL/HL Solvation with water as the solvent Solvation is the combination of a solvent with the molecules or ions of a solute. Polar solutes dissolve due to attraction between the partial positive and negative charges on water molecules and solute molecules. Positively charged ions are attracted to the partial negative oxygen pole of water. Negatively charged ions are attracted to the partial positive hydrogen pole of water. ▴ Glucose has polar hydroxyl groups (–OH) with oxygen having a partial negative charge and hydrogen a partial positive charge. Hydrogen bonds (········) form between these hydroxyl groups and water, causing solvation Osmosis Osmosis is a net movement of water across a membrane due to the attractions between solutes and water. Solutes are osmotically active if intermolecular attractions form between them and water. (Na, K, Cl, glucose) Concentration is the amount of solute per unit volume of solution.The volume is measured in cubic metres or decimetres (m³ or dm³). 1L = 1 dm³). The amount of solute is measured in moles, so a sodium chloride solution has a concentration of 0.5 moles dm -3 if a litre of solution contains half a mole of NaCl. ONLY HL Atmospheric pressure Water potential as the potential energy of water per unit volume The concept of water potential helps to The symbol for water potential is Ψ (the understand movement of water in living Greek letter psi) and the units for systems, especially plants. measurement are kilopascals (kPa) or Water potential is the facility which megapascals (MPa). seeds absorbs water. The absolute quantity of potential energy cannot be determined, so all values are relative. Pure water at standard atmospheric pressure and 20°C has been assigned a water potential of zero. Many factors influence water potential, but in living systems only two contributors vary in such a way that they need to be considered: 1. Hydrostatic pressure. Rises or falls in hydrostatic pressure change the potential energy of water. The higher the pressure, the more potential energy water has. More absorption of water by seeds. 2. Solute concentrations When solutes dissolve, the potential energy of water is reduced. The higher the solute concentration, the less potential energy water has. Solute potential Ψs = 0 Ψs = - 2000 If two of the potentials shown in the graph are known, the third can be determined using the nomogram. 1. Use the nomogram to determine the water potential of a plant cell with: a. solute potential −2 MPa and pressure potential +1 MPa b. solute potential 0 MPa and pressure potential −10 MPa c. solute potential −8 MPa and pressure potential +2 MPa d. Plant cells do not normally have a water potential greater than 0 MPa. Deduce the combinations of solute and pressure potentials that do not occur in plant cells. Page 660 Data-based questions: Water potentials in plant cells 1. a. −1 MPa; b. −10 MPa; c. −6 MPa; d. when the pressure potential is never more positive than the solute potential is negative; because soil/external water potential is not normally higher than in cells and water is lost from cells with a higher water potential than the soil/exterior; 4. a. root Ψw = −0.44 MPa; leaf base Ψp = +0.35 MPa; leaf tip Ψs = −1.29 MPa; Table 5 shows potentials in cells in the root of a maize plant and in the base and tip of a leaf. Cells in the tip of the leaf had completed their growth but cells at the base were still growing. Determine the missing potentials in the table using the nomogram or the water potential equation (Ψw =Ψs +Ψp). Movement of water from higher to lower water potential The potential energy of water changes if solutes dissolve in it—this component is Water potential allows us to predict the solute potential (Ψs). When solutes dissolve, direction in which there will be net movement the potential energy of water is reduced. With of water molecules. no solutes dissolved, the solute potential is Water moves from a higher to a lower water zero. Because it is impossible for water to potential because this minimizes its potential hold less than no solutes, the only possible energy. In a similar way rocks roll down hills, solute potentials are zero or negative. and atoms form chemical bonds with each other with minimization of potential energy as the motivator.  There is a net movement of water from a hypotonic solution to a hypertonic solution because the hypertonic solution has a higher concentration of osmotically active solutes. There is no net movement of water between two isotonic solutions because there is no difference between the concentrations of osmotically active solutes, so equal numbers of water molecules move between them. This is known as dynamic equilibrium.