Term
| all cell membranes are... |
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Definition
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Term
| what does partially permeable mean? |
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Definition
| they let through only some molecules |
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Term
| name 4 ways substances move across a plasma membrane |
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Definition
| 1 diffusion between cell walls structures = smaller molecules 2. dissolve in lipid layer & pass through 3. via special protein channels 4. via carrier proteins |
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Term
| name 6 functions of the plasma membrane |
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Definition
| 1. barrier between cell and environment (compartmentalisation) 2. regulates transport of materials in and out 3. may contain enzymes 4. allow cell recognition 5. cell signalling 6. may be site of chemical reactions |
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Term
| name 5 functions of membranes within the cells (i.e. membranes surrounding organelles) |
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Definition
| 1. compartmentalisation (separates organelle from cytoplasm) 2. can form vesicles to transport substances around the cell 3. partially permeable = controls ins and outs 4. there are membranes within organelles = barriers between membrane contents & rest of organelle 5. site of chemical reactions e.g. cristae in mitochondria |
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Term
| when was the fluid mosaic model 'invented'? |
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Definition
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Term
| what does the fluid mosaic model describe? |
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Definition
| the arrangement of molecules in the membrane |
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Term
| why is it a ''fluid'' mosaic model? |
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Definition
| because the bilayer is fluid due to constantly moving phospholipids |
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Term
| name nine things found in the phospholipid bilayer |
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Definition
| 1. lipid bilayer 2. glycocalyx (glycoproteins & glyolipids) 3. protein receptor sites 4. cholesterol 5. channel proteins 6. carrier proteins 7. peripheral proteins 8. cytoskeleton filaments 9. phospholipids |
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Term
| what forms the phospholipid bilayer? |
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Definition
| the attractions between the hydrobic tails of phospholipds, with the hydrophilic heads 'sticking out' |
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Term
| the centre of the bilayer between the tails in hydrophobic. what does this means it can allow through? |
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Definition
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Term
| the centre of the bilayer between the tails in hydrophobic. what does this means it cannot allow through? |
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Definition
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Term
| where is cholesterol found? |
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Definition
| between the phospholipids in the phospholipid bilayer - it binds to the tails to make it pack closer = membrane is less fluid |
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Term
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Definition
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Term
| name 3 functions of cholesterol |
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Definition
| 1. regulates fluidity of membrane 2. maintains mechanical stability 3. resists temperature change |
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Term
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Definition
| a protein with a chain of carbohydrate molecules attached |
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Term
| name 4 functions of glycoproteins & glycolipids |
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Definition
| 1. stabilise membrane (form hydrogen bonds with surrounding water molecules) 2. sites where drugs, hormones and antibodies bind 3. receptors for cell signalling 4. they're antigens |
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Term
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Definition
| a lipid with a carbohydrate chain attached |
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Term
| what do the glycoproteins and glycolipids form? |
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Definition
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Term
| name 2 types of protein found in the phospholipid bilayer |
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Definition
| channel proteins & carrier proteins |
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Term
| what do channel proteins allow through? |
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Definition
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Term
| by what processes do carrier proteins transport substances? |
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Definition
| active transport & facilitated diffusion |
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Term
| what other function can some proteins have? |
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Definition
| some act as receptors for molecules (e.g. hormones) in cell signalling |
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Term
| not all cell membranes have... |
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Definition
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Term
| where are protein channels and carriers found in neurones? |
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Definition
| in plasma membranes of the axon |
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Term
| what do the protein channels and carriers in the axon in neurones allow the entry & exit of? |
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Definition
| ions to bring about electrical conduction |
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Term
| what surrounds the axon of a neuron? |
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Definition
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Term
| what is the myelin sheath formed from? |
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Definition
| flattened Schwann cells (20% protein & 76% lipid) |
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Term
| white blood cells have special protein receptors. what does this allow? |
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Definition
| it allows them to recognise antigens on foreign cells |
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Term
| root hair cells have many carrier proteins. what does this allow? |
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Definition
| the active transport of nitrate ions from soil to cells |
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Term
| why is the inner membrane of mitochondria mainly protein, rather than lipid? |
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Definition
| because the inner membranes have many electron carriers which are made of protein |
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Term
| what do cells use to communicate in cell signalling? |
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Definition
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Term
| explain the stages in cell signalling |
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Definition
| 1. one cell releases a messenger molecule (e.g. hormone) 2. molecule travels to another cell called a target cell 3. molecule binds to receptor on its cell membrane = it is detected |
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Term
| in cell signalling, what do proteins in cell membranes act as? |
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Definition
|
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Term
| what do receptor proteins have? what does this mean? |
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Definition
| specific shapes = only messenger molecules with a complementary shape can bind |
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Term
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Definition
| a cell that responds to a particular messenger molecule |
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Term
| name one example of a messenger molecule |
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Definition
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Term
| when is glucagon released? |
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Definition
| when there isn't enough glucose in the blood |
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Term
| what does glucagon bind to? what does this cause? |
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Definition
| receptors on liver cells = liver cells break down stores of glycogen to glucose |
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Term
| name another example of a messenger molecule, other than glucagon |
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Definition
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Term
| when are antihistamines released? |
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Definition
| when cell damage occurs which releases histamines which bind to receptors of other cells causing inflammation |
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Term
| what is the job of antihistamines? |
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Definition
| block histamine receptors on cells = stops inflammation |
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Term
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Definition
| the movement of molecules from an area of high concentration of that molecule to low concentration of that molecule |
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|
Term
| does diffusion have to be across a membrane? |
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Definition
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Term
| is diffusion active or passive? |
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Definition
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Term
| what type of molecules does diffusion move? |
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Definition
| small, hydrophobic molecules |
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Term
| which direction do molecules travel in diffusion in terms of gradient? |
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Definition
| they travel down their concentration gradient (down gradient) |
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Term
| does diffusion require ATP? |
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Definition
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|
Term
| does diffusion require proteins? |
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Definition
|
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Term
| explain what happens in diffusion |
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Definition
| 1. molecules have high KE 2. at a high concentration they bump into each other = push each other away = spread out via net diffusion 3. travel down their concentration gradient until they are evenly dispersed & the molecules reach equilibrium (no net diffusion) |
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Term
| a steeper diffusion gradient = |
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Definition
| = faster the rate of diffusion |
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Term
| explain how different molecules diffuse across a membrane |
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Definition
| 1. lipid soluble molecules = diffuse straight through 2. water soluble molecules (lipid - insoluble) = have to pass through channel proteins 3. water = passes through channel proteins called AQUAPORINS |
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|
Term
| what maintains the concentration gradient in diffusion? |
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Definition
| by using molecules up in metabolic reacations |
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Term
| name 5 factors that affect the rate of simple diffusion |
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Definition
| 1. temperature 2. diffusion distance 3. surface area 4. size of diffusing molecules 5. concentration gradient |
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Term
| how does temperature affect the rate of diffusion? |
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Definition
| higher temp = higher KE = increased rate of diffusion |
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Term
| how does diffusion distance affect the rate of diffusion? |
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Definition
| the thicker the membrane across which molecules diffuse the slower the rate of diffusion |
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Term
| how does surface area affect the rate of diffusion? |
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Definition
| a larger cell membrane SA e.g. microvilli = greater rate of diffusion |
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Term
| how does the size of diffusing molecules affect the rate of diffusion? |
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Definition
| smaller ions/molecules diffuse more rapidly than larger molecules |
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Term
| how does the concentration gradient affect the rate of diffusion? |
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Definition
| steeper gradient = faster rate rate of diffusion |
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|
Term
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Definition
| the movement of molecules from an area of high concentration of that molecule to low concentration of that molecule |
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|
Term
| does diffusion have to be across a membrane? |
|
Definition
|
|
Term
| is diffusion active or passive? |
|
Definition
|
|
Term
| what type of molecules does diffusion move? |
|
Definition
| small, hydrophobic molecules |
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|
Term
| which direction do molecules travel in diffusion in terms of gradient? |
|
Definition
| they travel down their concentration gradient (down gradient) |
|
|
Term
| does diffusion require ATP? |
|
Definition
|
|
Term
| does diffusion require proteins? |
|
Definition
|
|
Term
| explain what happens in diffusion |
|
Definition
| 1. molecules have high KE 2. at a high concentration they bump into each other = push each other away = spread out via net diffusion 3. travel down their concentration gradient until they are evenly dispersed & the molecules reach equilibrium (no net diffusion) |
|
|
Term
| a steeper diffusion gradient = |
|
Definition
| = faster the rate of diffusion |
|
|
Term
| explain how different molecules diffuse across a membrane |
|
Definition
| 1. lipid soluble molecules = diffuse straight through 2. water soluble molecules (lipid - insoluble) = have to pass through channel proteins 3. water = passes through channel proteins called AQUAPORINS |
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|
Term
| what maintains the concentration gradient in diffusion? |
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Definition
| by using molecules up in metabolic reacations |
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|
Term
| name 5 factors that affect the rate of simple diffusion |
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Definition
| 1. temperature 2. diffusion distance 3. surface area 4. size of diffusing molecules 5. concentration gradient |
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|
Term
| how does temperature affect the rate of diffusion? |
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Definition
| higher temp = higher KE = increased rate of diffusion |
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|
Term
| how does diffusion distance affect the rate of diffusion? |
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Definition
| the thicker the membrane across which molecules diffuse the slower the rate of diffusion |
|
|
Term
| how does surface area affect the rate of diffusion? |
|
Definition
| a larger cell membrane SA e.g. microvilli = greater rate of diffusion |
|
|
Term
| how does the size of diffusing molecules affect the rate of diffusion? |
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Definition
| smaller ions/molecules diffuse more rapidly than larger molecules |
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|
Term
| how does the concentration gradient affect the rate of diffusion? |
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Definition
| steeper gradient = faster rate rate of diffusion |
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|
Term
| define facilitated diffusion |
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Definition
| the movement of molecules from an area of high concentration of that molecule to an area of its low concentration, across a partially permeable membrane via protein channels or carriers |
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|
Term
| which direction do the molecules travel in facilitated diffusion in terms of gradient? |
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Definition
| down a concentration gradient |
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|
Term
| is facilitated diffusion active or passive? |
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Definition
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Term
| does facilitated diffusion require energy? |
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Definition
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Term
| polar molecules/charged molecules, such as ions are lipid-insoluble because they cannot form interactions with the hydrophobic tails of the phospholipid bilayer. so how, via facilitated diffusion, do they travel across the bilayer? |
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Definition
| via protein channels filled with water embedded in the membrane |
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Term
| how big are water filled protein channels? |
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Definition
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Term
| large molecules e.g. glucose are too big to diffuse through the phospholipid bilayer? so how, via facilitated diffusion, do they travel across the bilayer? |
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Definition
| via transmembrane carrier proteins. there are specific carrier proteins for different types of molecules |
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Term
| neurone plasma membranes have many channels specific to either sodium or potassium ions. why is this important? |
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Definition
| the facilitated diffusion of these ions in and out of the axon allow the conduction of nerve pulses |
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Term
| plasma membranes of epithelial cells that line airways have chloride ion channels. why is this important? |
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Definition
| chloride ions play a crucial role in regulating the composition of mucus to trap particles and pathogens |
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Term
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Definition
| the movement of water from a higher water potential to a lower water potential across a partially permeable membrane |
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Term
| is osmosis active or passive? |
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Definition
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|
Term
| which direction does water travel in osmosis in terms gradient? |
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Definition
| down their concentration gradient |
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|
Term
| does osmosis require proteins? |
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Definition
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|
Term
| does osmosis require energy? |
|
Definition
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|
Term
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Definition
| measure of the tendency of water molecules to diffuse from one region to another |
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|
Term
| what has the highest water potential? |
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Definition
|
|
Term
| what is the units for water potential? |
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Definition
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|
Term
| what is the water potential of pure water? |
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Definition
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|
Term
| how can the water potential be lowered? |
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Definition
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Term
| what happens when an animal cell is placed in a solution with a higher water potential than itself e.g. pure water, a hypotonic solution? |
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Definition
| 1. water moves into cell by osmosis down a concentration gradient 2. cell swells and bursts 3. CYTOLYSED (permanently) |
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Term
| what happens when an animal cell is placed in a solution with a lower water potential than itself e.g. salt/sugar, a hypertonic solution? |
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Definition
| 1. water moves out of cell by osmosis down a concentration gradient 2. cells shrinks and appears wrinkled 3. CRENATED (not permanently) |
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Term
| what happens when a plant cell is placed in a solution with a higher water potential than itself e.g. pure water, a hypotonic solution? |
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Definition
| 1. water moves into cell by osmosis down a concentration gradient 2. plant cell wall stops it bursting 3. TURGID |
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Term
| what happens when a plant cell is placed in a solution with a lower water potential than itself e.g. salt/sugar, a hypertonic solution? |
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Definition
| 1. water moves out of cell by osmosis down a concentration gradient 2. cell membrane pulls away from cell wall 3. PLASMOLYSED |
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Term
| what is a plant tissue with plasmolysed cells known as? |
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Definition
|
|
Term
|
Definition
| the movement of substances against their concentration gradient (from low conc to high conc) across a cell membrane, using ATP and protein carriers |
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|
Term
| what direction do molecules travel in active transport, in terms of gradient? |
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Definition
| against their concentration gradient |
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|
Term
| does active transport require ATP? |
|
Definition
|
|
Term
| does active transport require protein carriers? |
|
Definition
|
|
Term
| what types of molecules does active transport move? |
|
Definition
|
|
Term
| where is the energy for active transport provided from? |
|
Definition
|
|
Term
| what type of protein is used in active transport? |
|
Definition
|
|
Term
| how many binding sites do carrier proteins have? |
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Definition
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|
Term
| what is the first binding site on a carrier protein specific to? |
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Definition
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|
Term
| what is the second type of binding site on a carrier protein specific to? what does this allow? |
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Definition
| ATP = allows it to hydrolyse and release energy to help protein 'change shape' to suit molecule/ion |
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|
Term
| give an example of where active transport takes place. explain |
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Definition
| root hair cells = move nitrates from a lower concentration in soil to a higher concentration in roots |
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|
Term
| give another example of where active transport takes place. explain |
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Definition
| guard cells = ATP from chloroplasts allows them to transport potassium ions from surrounding cells into guard cells |
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|
Term
|
Definition
| the movement of large molecules which are unable to move through carrier proteins |
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|
Term
| name the 2 types of bulk transport |
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Definition
| 1. endocytosis 2. exocytosis |
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|
Term
|
Definition
| the bulk movement of large molecules into a cell |
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|
Term
|
Definition
| 1. section of a cells plasma membrane surrounds the substance 2. plasma membrane then encloses the substance 3. it encloses it into a vesicle (phagosome) |
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|
Term
| name 2 examples of endocytosis |
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Definition
| 1. phagocytosis 2. pino(endo)cytosis |
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Term
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Definition
| the ingestion of solid matter |
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|
Term
| what is pino(endo)cytosis? |
|
Definition
| the ingestion of liquid matter |
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|
Term
| why is ATP required in endocytosis? |
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Definition
| to form and move vesicles using motor proteins |
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Term
|
Definition
| the bulk movement of large molecules out of a cell |
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|
Term
|
Definition
| 1. membrane-bound vesicle, containing the sequence to be secreted, is moved towards cell surface membrane from Golgi 2. cell membrane and vesicle fuse 3. fused site opens 4. releases contents out if vesicle and cell |
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|
Term
| why is ATP needed in exocytosis? |
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Definition
| to fuse the membranes and to move the vesicle |
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|
Term
| name an example of exocytosis |
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Definition
|
|
Term
| name 2 factors that affect membrane structure and permeability |
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Definition
| 1. temperature 2. chemicals/solvents/pH |
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|
Term
| what happens to membrane structure and permeability when temperature decreases? |
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Definition
| 1. saturated fatty acids become compressed 2. cholesterol buffers the effect of lowered temperature = prevents reduction in membrane's fluidity |
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|
Term
| what happens to membrane structure and permeability when temperature increases? |
|
Definition
| 1. phospholipids gain a greater KE = increased movement = increased permeability (more leaky) 2. phospholipid bilayer may melt 3. proteins denature 4. substances have more energy to move out of cell |
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|
Term
| what happens to membrane structure and permeability when a cell is surrounded by a solvent, such as ethanol? |
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Definition
| the solvent increases permeability, because solvents dissolve fatty substances, such as lipids = increases permeability |
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|
Term
| what happens to membrane structure and permeability when the pH of a cell changes? |
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Definition
| alkalis and acids may denature proteins = affects tertiary structure = increases permeability |
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|
Term
| Explain how you would test the effect of temperature on cell membranes of beetroot |
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Definition
| 1. cut 5 equal sized tubes of beetroot & rinse 2. place each tube in separate test tubes, each with 5cm3 of water 3. place each test tube in a water bath at different temperatures, e.g 10,20,30,40,50 degrees Celsius for the same length of time 4. remove the piece of beetroot, leaving the red pigment in the test tube 5. use a colorimeter 6. the higher the permeability of the membrane, the more pigment that has been released = higher absorbency of the liquid |
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|
Term
| what is the name of the pigment released from beetroot? |
|
Definition
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