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66 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is an excitable cell?
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A cell that can generate an action potential at its membrane in response to depolarisation and may transmit an impulse along the membrane.
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e.g. Neurons, Cardiac Myocytes, Skeletal Muscle cells
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Define Potential Difference. (PD)
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The difference in electrical potential between 2 points
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How does PD arise?
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1. Passive movement/Diffusion Driving Force (Electrochemical Gradient) 2. Partial Permeability of membrane (K+ not Na+) |
Active Transport: Against conc. and/or electrical gradient, requiring ATP.
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What factors affect permeability?
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1. Size 2. Electrical Charge 3. Molecular Shape 4. Solubility |
i.e. fat soluble, hydrophilic etc. Note: The different arrangement of lipids and proteins present cause differing permeabilities |
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In Rest state cells are...
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1. Fairly, readily permeable to K+ and Cl- 2. Poorly permeable to Na+ 3. Impermeable to large organic anions in cells (i.e. proteins) |
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Define Electrochemical Gradient.
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The difference in ion concentration and electrical potential from one point to another, so that ions move passively along it.
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Define Electrical Potential. Electrical Gradient?
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The PD between charged particles. The electrical gradient consists of ions moving down gradient. |
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What is the Nernst equation used for?
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For the conversion of the concentration into an equivalent electrical gradient.
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What does the Nernst equation tell us?
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The Equilibrium Potential of an Ion: The magnitude of the electrical gradient that exactly balances the conc. gradient of a given ion.
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Nernst Equation: (V_eq.: E or E_x) |
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In the Nernst equation what do x, R, T, z, F [x]o, [x]I stand for?
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x: Ion, R: Universal Gas Content T: Temperature z: Valence of ion F: Faraday's Constant [x]o: Conc. of x outside [x]I: Conc. of x inside |
Outside: Extracellular Matrix Cytoplasm: Inside Valence: +1 for K+, -1 for Cl- Therefore Valence=Charge |
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If the chemical and electric gradients are in the same direction...
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The net driving force is the sum of the 2 gradients.
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State the concentration of Na+, K+, Cl- and A- at resting membrane potential in the ICM.
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Na+:15mM K+: 150mM Cl-:10mM A-: 65mM |
ICM: Intracellular Matrix A-: Anion (proteins) |
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State the concentration of Na+, K+, Cl- and A- at resting membrane potential in the ECM.
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Na+:150mM K+: 5mM Cl-:108mM A-: 0mM |
ECM: Extracellular Matrix
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Goldman-Hodgkin-Katz equation (GHK) shows...
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How the membrane potential of a cell can be altered by charges in the relative permeability of its membrane to the ions. (without any change in the ionic gradients themselves)
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Inhibitory neurotransmitters cause IPSP which...
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Prevents action potential by making PD more negative, so depolarisation is harder. |
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Action potentials are...
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All-or-Nothing Responses |
What kind of response?
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What is Temporal Summation?
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When a series of AP in the presynaptic neuron causes an AP in the postsynaptic neuron. (EPSP) |
Summation: When several small potential changes combine to produce a larger change in PD across the membrane.
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What is Temporal Summation dependant upon?
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Depolarisation's: 1. Frequency of occurrence 2. Time between occurrences |
In vision: Buscan-Roscoe law of intensity and time
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What happens when the inhibitory and excitatory post-synaptic potentials are the same magnitude?
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They cancel out
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What is Spatial Summation?
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Several presynaptic neurons each contribute to an AP in postsynaptic neurones.
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Add/summate from dendrites Ricco's Law |
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What is the difference between Convergence and Divergence?
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C: Many neurons influence one D: One neuron influences many |
Con: Together Divert |
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Lipid membranes have capacitance, producing a voltage across a membrane...
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1. Charge=Current*Time 2. Voltage=Charge stored/Capacitance |
Capacitance: the ability to store charge Formulae of charge and voltage |
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Lipid bilayer is permeable to lipid soluble molecules. What explains its permeability to ions and polar molecules?
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The presence of Channel Proteins and Carrier Proteins. (e.g. aquaporin, ion channels etc.)
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Hydrophilic molecules are polar i.e. glucose, Na+, K+, Cl- etc. Hydrophobic molecules are lipid-soluble i.e. gases |
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Overall, ions and charged molecules move across the cell membrane due to 3 factors:
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1. Concentration Gradient 2. Charge of the molecule/ion 3. Membrane potential |
3 factors combine to give the electrochemical gradient
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What is the limitation of the Nernst equation?
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Intracellular and Extracellular concentrations must be known.
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How can the electrochemical gradient be calculated?
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The difference between the ion in question and the membrane potential. |
Membrane potential and ion |
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Direction is determined by the electrochemical gradient. What determines the rate of movement?
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1. The number of channels/carrier protein 2. The properties of the channels/protein |
1. Number of ... 2. Channel
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Describe the action of Na+, K+-ATPase.
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For each ATP molecule hydrolysed a cell pumps out 3 Na+ out in exchange for 2 K+ in
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Na+, K+-ATPase is also called the Sodium-Pump
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How does the sodium pump stabilize cell volume?
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By maintaining a low intracellular sodium concentration; Prevents increased osmolality resulting in osmosis inwards and cell swelling. |
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Define Threshold Value.
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The degree of depolarisation that triggers an action potential
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Note: Varies between different neurones and different parts of the same neurone
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Generally thicker fibres have...
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Lower thresholds so it's easier to stimulate an action potential.
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Note: In case u didn't know, nerve cells transmit signals by action potential
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How do Anaesthetics work?
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They increase the threshold value, by blocking voltage-gated Na+ channels
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Note: Finer nerves are most sensitive
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What is the Absolute Refractory Period?
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Voltage-gated Na+ ion channels are deactivated for 1ms Axons become unexcitable as AP is already happening. |
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What is the Relative Refractory Period?
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Duration: 5ms A strong enough stimulus can trigger another AP. As some channels become activated again. |
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What is Repolarisation?
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After Depolarisation: When V-gated Na+ channels are inactivated, K+ ion efflux down electrochemical gradient
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What accelerates the efflux of K+ ions ?
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The opening of V-gated K+ channels
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What is Accommodation?
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Nerve tissue's ability to adjust to a constant source and intensity so response is only due to increased intensity/duration. |
e.g. growing accustomed to a specific scent/odour
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What probably causes Accommodation?
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Reduced permeability to Sodium ions, resulting in increased threshold intensity and stabilisation of resting membrane potential.
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What poison occurs naturally in puffer fish? What's its course of action?
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Tetrodotoxin (TTX): blocks Na+ channels by binding to its extracellular side.
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What does Tetraethylammonium (TEA+) cause? How?
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Neuromuscular Paralysis: Blocks Potassium-selective channels in the nerve membrane, prolonging electrical impulse in axon terminals. This increases Acetylcholine release. |
Repolarisation can't occur
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Local currents occur in myelinated neurons. What are they?
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Na+ flows to inactive adjacent parts of the cell via diffusion.
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Ionic exchange occurs in Nodes of Ranvier only Quicker Deepolarisations |
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Compare Myelinated Neurons to Non-myelinated Neurons.
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M: Has a Myelin Sheath (Schwann Cells), Nodes of Ranvier allow faster conduction speed (Saltatory Conduction) N: Continuous Conduction; slower conduction speed, loosely wrapped in Schwann Cells. |
Myelin: white phospholipid covering around an axon
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What factors affect Conduction velocity?
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1. Resistance of axon to electrical current flow along its length 2. Axon membrane's electrical resistance 3. Axon membrane's electrical Capacitance 4. Myelination vs. Non-myelin. 5. Diameter Size of axon |
1: Internal Electrical Resistance 2: is higher in myelinated 3: is lower in myelinated 4. Saltatory>Continuous 5. Large Axon>Small Axon |
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How can we measure/record Action Potentials?
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By stimulating a nerve trunk through the skin and record the Compound Action Potential
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A less useful method for diagnostic purposes is to record AP from individual axons.
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What is a Compound Action Potential?
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The summed action potentials of all the different fibres present
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The AP of a Nerve Trunk is not All-or-nothing!!
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Graded Phenomena are dependant on the size of a stimulus affecting the number of fibres stimulated. What are the 3 Grades?
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1. Small Stimulus: Few fibres and small potential 2. Larger Stimulus: More fibres and larger potential 3. Maximum Stimulus: All fibres and maximum potential |
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Compound APs grow in amplitude as...
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The stimulus strength is increased above threshold until all axons in the nerve are recruited
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What is an Electrical Gradient?
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A difference in charges of 2 areas with ions or particles
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What are Ion channels? Channel Gating?
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1. Channels which have Selectivity and Gating. 2. Channel Gating: The fluctuation of the channel between open and closed states |
Ions go down their electrochemical gradient through pores. |
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How does membrane potential affect the electrochemical gradient?
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The inside of cells is always negative, with respect to the outside. Therefore, Positively charged chemical species are attracted and negative are repelled. |
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What 4 factors affect Gating?
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1. Mechanical stretch of the Plasma membrane 2. Membrane Voltage 3. Extracellular Agonists/Antagonists (e.g. ACh) 4. Intracellular messengers (e.g. Ca++, ATP, cGMP) |
1. Stretch 2. Voltage 3. OutsideMessenger 4. Inside messenger |
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Ionotropic Receptors can...
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Transport many ions per pore (which opens when activated)
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Ion Channel=Ionotropic Receptor
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There are 2 types of ionotropic receptors. What are they? Functions?
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1. Ligand-Gated Channels 2. Voltage-Gated Channels (opens pore when PD decreases) 3. Both are used for short term signalling. |
Both types have Na+ versions |
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What are Metabotropic Receptors?
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Activation of this Receptor initiates Intracellular signalling mechanism; long term signalling
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Note: Ions do not pass through this Receptor protein
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Give 3 examples of Metabotropic Receptors.
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1. G-Protein Complex Receptors 2. Metabotropic Glutamate Receptors 3. Adrenergic Receptors |
1. Exists as Alpha, Beta & Gamma, converts GTY to GDP 2. Plays a role in learning memory, can change membrane protein functions (e.g. enzyme) 3. Beta ones in the heart |
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Membranes restrict the movement of...
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Hydrophilic/polar solutes (Glucose, ions, amino acids)
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Note: Gases (i.e. CO2 O2) and ethanol can pass through; lipid soluble
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Aquaporin (water channel) allows influx/efflux of water. How is this regulated?
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1. Changing no. of Aquaporin 2. Changing its permeability (e.g. By Gating with pH) |
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List 3 types of Solute carriers. (Carrier proteins that carry solutes across the membrane)
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1. Antiporters/Exchangers/Counter Transporters 2. Symporters/Cotransporters 3. Uniporters |
1. Couple movement of 2+ molecules/ions across the membrane in opposite directions. 2.Couple movement of 2+ molecules/ions across the membrane; same direction. 3. Transports single molecules across |
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Give an example of each Solute Carrier.
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1. Na+-H+ antiporter for pH regulation, Sodium Pump 2. NKCC2/Na+K+2Cl- Symporter used for urine dilution/conc. 3. GLUT2 brings Glucose into cell |
1. Sodium 2. Kidney 3. Small intestine
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Give some examples of ATP dependant ion transporters.
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1. Sodium pump 2. H+-ATPase (Vacuolar and Plasma Membrane Variations) 3. ABC Transporters |
Vacuolar: found in intracellular organelles like lysosomes Plasma Membrane: Important in Urinary Acidification 3. Cystic Fibrosis Transmembrane Regulator (CFTR) |
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Define Primary Active Transport.
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Transport directly coupled to ATP Hydrolysis |
ATP |
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Define Secondary Active Transport.
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Where energy in the electrochemical gradient of one molecule is used to move another against its electrochemical gradient.
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Note: Membrane Transport failure causes diseases
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What is Facilitated Diffusion?
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The passive transport of molecules down their electrochemical gradient, with the help of transmembrane proteins (i.e. Channels/Carriers) |
Channels and carriers
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Give an example of Secondary Active Transport.
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Transport of Glucose across the epithelium of the small intestines. (SGLT1 couples Na+ with Glucose, GLUT2 then pumps it into blood) |
SGLT-1
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Give an example of Primary Active Transport.
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Root hair cells in plants actively transport ions from the soil into the plant. |
Plant |
