How does the bilayer formed by phospholipids affect entry and exit of substances into and out of a cell? (2 marks)
The phospholipid bilayer forms a barrier that prevents the movement of polar and large substances across the membrane
Explain the diffusion of oxygen through a cell surface membrane (2 marks)
There is net movement from higher to lower concentration
Oxygen molecules can pass between phospholipid molecules in the bilayer
It is a passive process
The rate of diffusion is dependant on the steepness of the concentration gradient
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How does the bilayer formed by phospholipids affect entry and exit of substances into and out of a cell? (2 marks)
The phospholipid bilayer forms a barrier that prevents the movement of polar and large substances across the membrane
Explain the diffusion of oxygen through a cell surface membrane (2 marks)
There is net movement from higher to lower concentration
Oxygen molecules can pass between phospholipid molecules in the bilayer
It is a passive process
The rate of diffusion is dependant on the steepness of the concentration gradient
Explain the facilitated diffusion of glucose through a cell surface membrane (2 marks)
There is a net movement from higher to lower concentration
Using a carrier/channel/intrinsic protein
The proteins have a specific tertiary structure that is complementary to the glucose
Binding of the glucose changes the shape of the protein so the glucose passes across the membrane
It’s a passive process
Explain the active transport of sodium ions through a cell surface membrane (2 marks)
There is movement from a lower to higher concentration
A protein carrier with a specific tertiary structure to its receptor site that is complementary to the sodium ion is required
Energy/ATP is required
The protein carrier requires the energy/ATP to change shape when the sodium ions bind so that they can be transported across the membrane
What property allows substances to diffuse through plasma membranes?
Non-polar