How are phospholipids arranged in a plasma membrane?
In a bilayer with hydrophobic tails inside which repels water and hydrophilic outside which attracts water.
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What are the functions of phospholipids in the membrane?
to allow lipid soluble substances to enter and exit the cell, to prevent water soluble substances leaving or entering the cell and to make the membrane flexible and self sealing.
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Why are some proteins in the surface of s bilayer?
act as mechanical support or as cell receptors
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What are the two types of proteins within the phospholipid bilayer?
protein channels and carrier proteins
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Give two functions of proteins in plasma membranes.
receptors, carriers, channels, enzymes and antigens.
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How does a plasma membrane adapt for its function?
Phospholipid bilayer forms a barrier to water soluble substances. The bilayer is a fluid which can bend to take up different shapes for phagocytosis. Channel proteins allow water soluble substances in through faciliated diffusion.
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Why is the structure of a plasma membrane described as a fluid mosaic?
The fluid allows the molecules to move and gives the membrane flexibility as its constantly changing in shape. It's mosaic as the proteins and phospholipids are embedded in bilayer
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How do substances move across cell surface membranes by facilitated diffusion?
Through the carrier/ channel proteins, the proteins is specific to the substance which then moves down the conc gradient
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Why is it called facilitated diffusion?
Because the movement of molecules is made easier by channels and carriers which span the membrane.
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Why does the diffusion of chloride ions involve a membrane proteins and o2 doesn't?
chloride ions are water soluble which cant cross the lipid bilyaer so the chloride ions are transported by facilitated diffusion. O2 is not a charger molecule therefore, o2 can't diffuse across the bilayer.
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What are the key features of osmosis?
it is the net movement of water from a high to low water potential across a partially permeable membrane which does not require energy.
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What is the water potential of pure water?
0
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What region does osmosis move in?
less negative water potential to more negative water potential as it is less pure.
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High conc of fertiliser in soil causes plants to wilt. Why?
Because the soil would have a lower water potential which prevents the roots from taking up water from the soil. So the pkants lose water by transpiration and the plant loses water to the soil by osmosis.
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Describe what happens when a cell is placed in a solution which is more concentrated.
membrane pulls away from the cell wall which makes it go flaccid. Water then moves down the conc gradient so water is lost from the cell by osmosis.
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Why would a potato cell increase in length if placed in distilled water?
because the water has a less negattive water potential so water enters the potato by osmosis which causes the cell to become turgid.
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Why would a potato cylinder show no more change by decreasing in length after 40 mins in a sucrose solution?
all water has moved out, cell wall prevents shrinkage, water potential are equal which gives an equilibrium, no net movement of water.
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What are the key features of active transport?
moves against the conc gradient, uses energy from respiration, more mitochondria in cell for more O2 uptake.
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How does cell surface membrane of cells in uterus may be adapted to allow rapid transport of nutrients?
the membrane is folded which increases the SA, there are many protein channels for FD, lots of protein carriers for AT.
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Explain how the cells lining the ileum absorb glucose by co transport with NA ions
sodium ions actively transported from ileum to blood, maintains diffusion gradient for sodium to enter cells from the gut. Glucose enters by FD with sodium ions.
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Other cards in this set
Card 2
Front
What are the functions of phospholipids in the membrane?
Back
to allow lipid soluble substances to enter and exit the cell, to prevent water soluble substances leaving or entering the cell and to make the membrane flexible and self sealing.
Card 3
Front
Why are some proteins in the surface of s bilayer?
Back
Card 4
Front
What are the two types of proteins within the phospholipid bilayer?
Back
Card 5
Front
Give two functions of proteins in plasma membranes.
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