Transport across cell surface membrane

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  • Created by: Laellex
  • Created on: 23-03-16 11:07
What are all membranes known as?
Plasma membranes
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What is the cell-surface membrane?
The plasma membrane that surrounds the cell
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What does the cell-surface membrane establish
Different conditions inside and outside of the cell
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What is a bilayer?
A structure formed by phospholipids
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Structure of the phospholipids in the bilayer?
The hydrophilic head points to the outside of the membrane attracted to water, and the hydrophobic tail points to the centre repelled by water
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Functions of the phospholipid bilayer?
Allow lipid-soluble substances in and out of cell, prevent water-soluble substances + flexibility/self-sealing
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Functions of proteins that occur on the surface of the bilayer?
Mechanical support + form cell-surface receptors in conjunction with glycolipids
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The function of protein channels?
Form water filled hydrophilic tubes, that allow water-soluble charged particles (ions + polar ones) across
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The function of carrier proteins?
Binds to large molecules then changes shape to move them across
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What property allows cholesterol molecules to prevent water loss/dissolved ions?
They are very hydrophobic
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How do cholesterol molecules reduce lateral movement
They pull together the fatty acid tails of the phospholipid molecules
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What are glycolipids made from?
A lipid with a carbohydrate attached by a glycosidic bond
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Function of glycolipids?
They extend from the bilayer to the watery outside environment acting as cell-surface receptors for specific chemicals (e.g. human ABO blood system)
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What are glycoproteins?
Proteins with a carbohydrate attached
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Function of glycoproteins?
Act as cell-surface receptors for hormones and neurotransmitters
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What molecules can't diffuse across C.S.M?
Molecules; not soluble in lipids, too large, charged: polar + ions
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What is the CSM 'fluid'?
The individual phospholipid molecules are constantly moving
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Why is the CSM 'mosaic'?
The proteins embedded in the bilayer vary in shape, size and pattern
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Examples of passive processes?
Diffusion (simple + facilitated diffusion) & osmosis
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What is diffusion?
The net movement of particles from a region of high concentration to low concentration- until equilibrium is reached
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What few molecules can diffuse across membranes?
Small, non-polar molecules
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Example of these molecules?
Carbon dioxide + oxygen
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Which molecules are transported by facilitated diffusion?
Charged ions + Polar molecules
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Which proteins are involved in facilitated diffusion?
Carrier proteins + Channel proteins
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Definition for osmosis?
The passage of water molecules from a region of high water potential to a lower water potential, through a selectively permeable membrane
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Which proteins span the bilayer?
Carrier proteins and channel proteins
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What is water potential?
The pressure created by water molecules
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What's water potential measured in?
Kilo pascals (kPa)
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Pure water has a high water potential of what value?
0 kPa
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The more negative the value...
The more concentrated the solution and lower water potential
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What are solutions with the same water potential called?
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For osmosis to occur the membrane must be...
Selectively permeable
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Water is polar, but why can it cross a membrane by simples diffusionism?
Because it is relatively small
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Why can't charged particles cross a membrane by simple diffusion?
They're water soluble and the centre of the phospholipid bilayer is hydrophobic?
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What does the rate of simple diffusion diffusion depend on?
Concentration gradient, surface area, thickness of exchange surface
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What does the rate of facilitated diffusion depend on?
Concentration gradient, amount of carrier/channel proteins
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What does the rate of osmosis depend on?
W.P Concentration gradient, surface area and thickness of exchange surface
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What happens to the concentration gradient as diffusion occurs?
It decreases until equilibrium is reached, then it levels off
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How do you find the water potential of cells/tissues?
Place them in a series of solutions with different water potentials. Where there is no net gain or loss, the w.p of the cell/tissues is the same as the solutions.
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What causes an animal cell to shrink and shrivel?
If it's placed in a solution with a lower water potential, water will leave the cell by osmosis
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If an animal cell is placed a solution with a higher water potential what happens?
It swells and bursts
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How are animal cells prevented from bursting?
Exist in solutions with the same water potential as them- blood plasma
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What 3 parts can plant cell be divided in for the explanantion of osmosis?
Central vacuole, protoplast + cellulose cell wall
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What is the central vacuole?
Sac containing a solution of sugars, salts + organic acids in water
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What does the protoplast contain?
The outer C.S.M, inner vacuole membrane, cytoplasm + nucleus
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What is the cellulose cell wall?
A tough, inelastic covering that is permeable to even large molecules
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What is turgidity?
Water enters plant cell and then protoplast swells and presses on the cell wall
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At what stage does the protoplast doesn't push against the cell wall?
At incipient plasmolysis
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What does it mean if a plant cell is plasmolysed?
When the protoplast pulls away from the cell wall, due to loss of water of by osmosis
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What is active transport?
The movement of molecules/ions from in or out of a cell from a region of low to high concentration
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Why is active transport an active process?
It require metabolic energy, in the form of ATP
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What protein does active transport involve
Carrier proteins
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Does AT go down or against a concentration gradient?
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Factors affecting AT?
Amount and speed of carrier proteins, rate of respiration
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What factors doesn't affect active transport?
Concentration gradient
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Other cards in this set

Card 2


What is the cell-surface membrane?


The plasma membrane that surrounds the cell

Card 3


What does the cell-surface membrane establish


Preview of the front of card 3

Card 4


What is a bilayer?


Preview of the front of card 4

Card 5


Structure of the phospholipids in the bilayer?


Preview of the front of card 5
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