Topic 2B: Cell membranes

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What does partially permeable mean?
Some substances move through and some don't
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By what 3 processes can substances move across a cell-surface membrane?
Diffusion, active transport or osmosis
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What's the difference between a cell membrane and plasma membrane?
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What is the function of the cell surface membrane?
They control what substances go in and out of the cell
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What is a bilayer?
A double layer
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What do receptor molecules on the cell membrane do?
They allow the cell to detect chemicals released from other cells
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What do phospholipids form on the cell surface membrane?
They form a barrier to dissolved (water soluble) substances
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What part of a phospholipid is hydrophillic?
The head
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Is the tail on a phospholipid hydrophobic or hydrophillic?
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Suggest the function of the membrane surrounding a chloroplast
To keep the enzymes needed for photosynthesis all in one place
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Why is the phospholipid bilayer described as fluid?
Because the phospholipids are constantly moving
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Describe the movement of glycoproteins within the bilayer
Some proteins are fixed in position, some move sideways
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What is a glycoprotein
A protein with a carbohydrate attatched
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How does the cell-surface membrane control what enters and leaves the cell?
Some proteins in the membrane allow the passage of large or charged particles that would otherwise find it difficult to pass through the membrane
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Describe the role of cholesterol in a cell membrane
It helps makes the membrane less fluid and more stable. It maintains the shape of animal cells and creates a barrier to polar substances
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In what type of cell would you expect to find cholesterol and why?
Red blood cell to maintain its shape as it has no neighbouring cells to help support it
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How does cholesterol create a barrier to polar substances in the cell membrane?
It has hydrophobic regions
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What substances can diffuse through the phospholipid bilayer?
Small, non polar substances and water
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What practical investigates the permeability of cell membranes?
The betroot one when you add alcohol and something happens
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What happens to the phospholipid bilayer at temperatures of 45 degrees and over?
It starts to melt/break down and it becomes more permeable. Channel/carrier proteins denature so they can't control what enters/leaves the cell, increasing permeability also
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At what temperatures is the membrane partially permeable?
Between 0 and 45 degrees
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Why don't phospholipids move much at temperatures below 0 degrees?
The don't have much energy lol
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How is the permeability of the cell membrane increased at temperatures below 0?
The channel proteins and carrier proteins have denatured, and ice crystals may form and pierce the membrane, making it permeable when it thaws
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What is diffusion?
The net movement of particles from an area of high concentration to an area of low concentration
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What is simple diffusion?
When molecules diffuse directly through a membrane
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What is facilitated diffusion?
The diffusion of particles through carrier proteins or channel proteins in the plasma membrane
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What 3 factors affect rate of diffusion?
Concentration gradient, surface area and thickness of exchange surface
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Does facilitated energy require energy?
No (bc its passive)
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What do carrier proteins move across the membrane?
Large molecules
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What do channel proteins move across the membrane?
Charged particles
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How do carrier proteins work?
A large molecule attatches to them, then it changes shape releasing the molecule on the opposite side of the membrane
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What 2 factors affect the rate of diffusion?
Concentration gradient & the number of channel/carrier proteins
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Explain how increasing the concentration gradient will affect the rate of diffusion?
The higher the concentraion gradient, the faster the rate of diffusion
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What is water potential?
The potential (likelihood) of water molecules to diffuse out or into a solution
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What is osmosis?
It is the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to lower water potential
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What is the water potential of pure water?
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Finish this sentence: the more negative the water potential, the...
..stronger the concentration of solutes in the solution
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What does isotonic mean?
Basically when two solutions have the same water potential
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What will happen to cells when they're put into a solution with higher water potential?
The cell will swell as water move into it by osmosis
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What are hypotonic solutions?
Solutions with a higher water potential compared to the inside of a cell
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What is a hypertonic solution?
Solutions with a lower water potential than the inside of a cell
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What happens to a cell when it is placed into a solution with a lower water potential?
It will shrink as water moves out of it by osmosis
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What 3 factors affect the rate of osmosis?
Water potential gradient, the thickness of the exchange surface and the surface area of the exchange surface
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What are the 2 main differences between active transport and facilitated diffusion?
Active transport moves solutes from a low to high concentration (in facilitated its high to low) & active transport requires energy (facilitated does not)
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Describe the chemical reaction that occurs to release energy in a cell
ATP undergoes a hydrolysis reaction, splitting into ADP and inorganic phosphate (Pi)
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What are co-transporters?
Type of carrier protein that bind two molecules together at a time, using one of the molecule's concentration gradient to move the other.
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What 3 factors affect the rate of active transport?
Speed of individual carrier proteins, the number of carrier proteins and the rate of respiration/availability of ATP
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Why are sodium ions important in the transport of glucose from the ileum to the blood?
Because sodium ions diffuse out of the lumen of the ileum and through the sodium-glucose co-transporter down its conc gradient, carrying glucose with it against its own conc gradient into the blood from the epthelium cell
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Other cards in this set

Card 2


By what 3 processes can substances move across a cell-surface membrane?


Diffusion, active transport or osmosis

Card 3


What's the difference between a cell membrane and plasma membrane?


Preview of the front of card 3

Card 4


What is the function of the cell surface membrane?


Preview of the front of card 4

Card 5


What is a bilayer?


Preview of the front of card 5
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Really helpful, thanks


since when can a word be shortened in a crossword .

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