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How Facilitated Diffusion Works
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How can cells control diffusion? One way in which cells can control diffusion is through the control of movement of particular types of molecules. Some molecules can pass freely through a cellular membrane. Large polar molecules and ions cannot diffuse through the lipid bilayer. Carrier proteins can move molecules across the membrane. Cells will have carrier proteins for specific molecules. These molecules will pass freely across the membrane while other molecules will not. The types of carrier proteins found on a cell are related to cell function.

View the animation below, then complete the quiz to test your knowledge of the concept.





1Facilitated diffusion requires
A)enzymes.
B)carrier proteins.
C)lipid carriers.
D)carbohydrate carriers.
E)lipid or carbohydrate carriers.


2Facilitated diffusion occurs
A)into the cell only.
B)out of the cell only.
C)in either direction depending on the temperature.
D)in either direction depending on the concentration gradient of the molecule.
E)in either direction depending on the size of the molecule.


3Facilitated diffusion is used to transport
A)sugars and amino acids.
B)H2O and O2.
C)CO2 and O2.
D)CO2 and H2O.
E)sugars and H2O.


4Unlike simple diffusion, facilitated diffusion requires energy expenditure by the cell.
A)True
B)False


5Facilitated diffusion requires a specific transporter for a specific molecule.
A)True
B)False





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