2.5- Biological Membranes

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  • Created by: McTighe
  • Created on: 11-02-18 10:32
Fill in the gap 'Cell membranes are ....... ....... barriers'
Partially Permable
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Name three roles of membranes
1.Barrier between cell and its environment/between organelles and cytoplasm 2.Site of chemical reactions 3.Site of cell communication (cell signalling)
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What is a partially permable membrane?
A membrane that is permable to small molecules of water and certain solutes, but does not allow the passage of large solute molecules.
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How wide is the the cell plasma membrane?
Approx 7nm
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Name three ways substances can move into the cell
1.Small molecules to diffuse 2.Substance can dissolve in lipid layer and pass through 3.Other substances can pass through protein channels or carrier proteins
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Describe the role of the plasma membrane at the surface of cells
-Seperates cell's components from environment -Regulate transport of material -Contains enzyme for specific metabolic pathways -Has antigens -Release chemical signals to other cells -Contain receptors for chemical signal -Site of chemical reactions
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Describe the role of a membrane within cells
-Organelles have membranes to seperate them from cytoplasm -MItochondria has two membranes for aerobic respiration -Chloroplast have two membranes for photosynthesis -Creates vesicles -Provides surface for attachement of enzymes
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What is the Phospholipid bilayer mainly made out of?
Phospholipids
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Describe a phosopholipid
It has a hydrophilic head which are in contact with external environment, and hydrophobic tails (fatty acids) which are in the centre of the membrane
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What is the name of the model which shows cell membrane structure
Fluid Mosaic Model
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What does the fluid mosiac model actually show?
A model which explains how cell membrane could be more dynamic and interact with cell's environement
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What is the role of glyoprotein in the cell membrane?
A carbonhydrate attached to a protein molecule- USed for cell recognition -Used for cell signalling -Has antigens -Has receptors for hormones -Hold cells together -Attach to water molecules to stabilise membrane
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What are surface proteins anchored by?
Amino acids
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What is the role of a glycolipid?
A carbohydrate chain attached to lipid- Used for cell signalling -Used for cell recognition -USed for receptor sites -Used for stabilising cell shape -Provides anitgens
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What is the purpose of Cholesterol?
Stabilises membrane and regulates fluidity
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What is the function of a phospholipid?
Provides barrier to large polar molecule
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What is the purpose of a channel protein?
Allows movement of large substances in/out of cell
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What is the purpose of a carrier protein?
Change shape to carry specific molecules in active transport or faciliated diffusion
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What is the role of membrane-bound receptors?
Where hormones and drugs can bind
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How is a neurons cell membrane specalised for its function?
Have protein channels/ carriers covering the long axon to allow entry/exit of ions to bring the conduction of electrical impulses along their length
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How is a white blood cell plasma membrane specialised for its function?
Contains special receptors that enables them to recognise antigens on foreign cells
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How is a root hair cell plasma membrane specialised for its function?
Have carrier proteins to actively transport nitrate ions from soil into the roots
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What is cell signalling?
The idea that a molecule released from one cell attaches to another cell and can create change in that cell
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How do cell membranes contribute to cell signalling?
-Release signal molecules by exocytosis -Proteins act as receptors -These receptors are specific and complementary in shape -Cell membrane allows entry of some signal molecules
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What is diffusion?
Passive Movement of molecules from an area of high concentration to an area of low concentration
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What type of molecules can move across a cell membrane using simple diffusion?
Very small ,no-polar molecules (e.g.O2 or CO2)
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How do the molecules move without a carrier protein?
All molecules have kinetic energy so move freely. The molecules will bump into each other as they randomly move and spread out
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When does diffusion end?
When the concentration gradient becomes equilibrium
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What is Fick's Law?
(Surface area X Concentration gradient) / Thickness of diffusion surface
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Name the five factors that affect simple diffusion?
Temperature, Diffusion distance, Surface Area, Size of diffusing molecules, Concentration gradient
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How does temperature affect simple diffusion?
As temperature increases, molecules have kinetic energy, causing them to move faster so rate of diffusion increases
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How does Diffusion distance affect simple diffusion?
The thicker the membrane across which molecules have to diffuse, the slower the rate of diffusion
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How does Surface area affect simple diffusion?
Move diffusion takes place across a larger surface area, cells specialised for absorption have extensions (Microvilli) to increase surface area
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How does the size of the diffusing molecules affect simple diffusion?
Smaller ions and molecules diffuse more rapidly than larger molecules as they move faster
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How does the concentration gradient affect simple diffusion?
The steeper the gradient, the faster the diffusion to the side where there are fewer molecules, down the gradient
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What is concentration gradient?
Difference between concentration
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What is faciliated diffusion?
Moves from a high concentration to a low concentration, requires protein transporters
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What is a transmembrane carrier protein?
A carrier protein that moves large molecules across a membrane, as they are too large to diffuse across. They are specific carrier proteins for different types of molecules (complementary in charge, size, shape)
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How does a carrier protein work?
The molecules bond to the carrier, move across the membrane. The molecules use their inbuilt kinetic energy to bind with the channel protein, which moves it to the other side of the membrane
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Give examples of molecules which would be carried by a carrier protein
Glucose, Amino acids
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What is a channel protein?
A channel which moves small ,polar molecules across membrane. Ions are insoluable in Lipid as they cannot interact with hydrophobic tails
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How wide are channel proteins?
Approx 0.8nm
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Why does water fill the channel?
So only soluble molecules can move through it
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How is Neuron specialised to control the number of molecules in and out?
Contains Na+ and K+ channels for ions. If all Na+ channels are closed, some K+ channels are open, more permable to potassium. This diffusion is crucial for conduction of nerve impulses
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How are KIdney collecting duct used to control number of molecules that move in/ out?
ADH increases insertion of aquaporins. More aquaporings increase permeability of the collecting duct to water, increasing diffusion
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What is Osmosis?
The movement of water across a partially pemable membrane from a higher water potential to a lower water potential, and therefore move down the water potential gradient
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What is the solvent in an aqueous solution?
Water
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What do aquaporins do?
Increase speed that water molecules can cross the membrane
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What is a hypertonic solution?
More solute, less water (concentrated)
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What is a hypotonic solution?
Less solute, more water (Dilute)
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What is an Isotonic solution?
Equal solute, equal water (equilibrium)
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Which way do solute move?
from hypotonic to hypertonic
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What is a Osmotic concentration?
Relates dissolved solutes in a solution (insoluble substances do not affect the concentration)
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What is water potential?
The number of water molecules in a solution
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What is water potential measured in?
Kilopascals (KPa)
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Is 0 high water potential or low water water potential
The highest (Pure water). The more solute, the more negative it is
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What way do solute molecules move?
Down the concentration gradient- From a high water potential to a low water potential
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What is the equation to work out Water potential?
Solute potential (-ve) + Pressure potential (+ve)
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What is solute potential?
The negative value measuring how much solute a solution contains. The bigger the solute amount, the lower the water potential
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What is pressure potential??
The positive value which is the hydrostatic pressure potential. The higher the pressure, the bigger the water potential
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Why is water potential in cells lower than pure water?
Due to solutes in cytoplasm and vacuole
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What happens if an animal cell is placed in pure water?
The water molecules move into the cell (From high water potential to lower water potential), causing the cell to increase in size. There is no cell wall to prevent it from bursting so the cell membrane bursts
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What is this process known as?
Cytolysed/Lysis
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What happens if an plant cell is placed in pure water?
The water molecules move into the cell (From high water potential to lower water potential), causing the cell to increase in size. The cell wall prevent it from bursting so the cell membrane pushes up against the cell wall
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What is this process known as?
Turgid
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Why is turgidity useful in plants?
It helps support the cell and maintain shape
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What happens to animal cells when placed in a solution with a lower water potential than the cell?
The water molecule move out of the cell (From a high water potential to a low water potential). This causes the cell membrane to shrivel up and shrink.
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What is this process known as?
Crenated
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What happens to plant cells when placed in a solution with a lower water potential
The water molecule move out of the cell (From a high water potential to a low water potential). The cell membrane pulls away from the cell wall
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What is this process called?
Plasmolysed
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What is a group of Plasmolysed cells called?
A Flaccid
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What is active transport?
The movement of substances against their concentration gradient across a cell membrane, using ATP (From a low concentration to a high concentration)
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How is energy provides for Active transport?
ATP is hydrolysised, by removing a phosphorus group from the phosphorylated nucleotide.
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When does active transport occur?
When a cell needs to accumulate more of a particular substance, that they could not get by diffusion alone
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How do carrier proteins help in active transport?
They have specific regions that only certain molecules can move in. The energy from ATP helps the protein to change its conformation, and this allows a molecule to be carried from one side to another
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What is the sodium-potassium pump used for?
It causes sodium ions to be outside the cell and potassium ions inside the cell
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Describe the process of the sodium-potassium pump
1.2Na+ ions inside cell bind to pump 2.Phosphate group from ATP breaks off releasing energy which changes shape of carrier protein 3.Sodium ions are released out of cell 4. 2K+ ions bind outside of cell, and move into cell with help of energy
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Describe how Root hair cells use active transport
1.Nitrates are dissolved in water, lowering water potential. In cell is lower than outside of cell 2.Nitrates move by active transport from soil into cell 3.Makes water potential in cell even lower 4.Water molecules move from soil into cell
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Describe how guard cells use active transport
1.K+ ions are dissolved in water in cell 2. K+ ions move from low potential to high into cell 3.Water potential in cell in low so water molecules move into cell
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What happens when water moves into guard cells?
Stomata opens up and allow gases to diffuse in and out of cell
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What is Bullk transport?
A form of active trasnport when molecules which are too large to pass through plasma membrane is brought in by a vesicle
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What is Endocytosis?
How large molecules are brought into a cell, by a segment of the cell membrane forming around it and brought in by a vesicle
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What is Pinocytosis?
Form of Endocytosis where solutes or fluids are brought in
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What is Phagocytosis?
Form of Endocytosis where large particles or solids are brought in
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Give an example of Endocytosis
White blood cells attacking a pathogen- The Phagocytic cell approaches the pathogen, cell membrane expands around pathogen. Pathogen is moved into cell by vesicle and lysosomes produce digestive enzymes to destroy pathogen
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What is Exocytosis?
Substances are released from cell through a vesicle
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Give an example of Exocytosis
Synapses- Chemicals in vesicles are moved by motor proteins along cytoskeletal threads in the pre-synaptic membrane. The vesicle membrane and plasma membrane fuses and neurotransmitter chemicals are released
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What happens when the temperature decreases?
- saturated Fatty acids in bilayer compress, bu unsaturated fatty acids also compresss (kinks push adjacent molecules away- mintain membrane fluidity). Proportion of unsaturated and saturated determines membrane fluidity at cold temperatures.
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What happens to cholesterol when temperatures decrease?
It buffers effect of low temperatures and prevents reduction in the membrane's fluidity. It does this by preventing phospholipids from packing too closely, reduces permability
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What happens when the temperature increases?
Phospholipids have more kinetic energy so move around more increase membrane fluiditiy. Permability increases. Affects proteins functions (e.g. Enzymes). Increase in fludility affect infolding of plasma membrane during phagocytosis
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How does cholestrol buffer the change in temperature?
reduces the increase in membrane fluidity
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Card 2

Front

Name three roles of membranes

Back

1.Barrier between cell and its environment/between organelles and cytoplasm 2.Site of chemical reactions 3.Site of cell communication (cell signalling)

Card 3

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What is a partially permable membrane?

Back

Preview of the front of card 3

Card 4

Front

How wide is the the cell plasma membrane?

Back

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Card 5

Front

Name three ways substances can move into the cell

Back

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