Plasma Membranes, Diffusion and Active Transport

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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)

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The phospholipid bilayer forms a barrier that prevents the movement of polar and large substances across the membrane

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Explain the diffusion of oxygen through a cell surface membrane (2 marks)

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  1. There is net movement from higher to lower concentration

  2. Oxygen molecules can pass between phospholipid molecules in the bilayer

  3. It is a passive process

  4. 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

2
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Explain the diffusion of oxygen through a cell surface membrane (2 marks)

  1. There is net movement from higher to lower concentration

  2. Oxygen molecules can pass between phospholipid molecules in the bilayer

  3. It is a passive process

  4. The rate of diffusion is dependant on the steepness of the concentration gradient

3
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Explain the facilitated diffusion of glucose through a cell surface membrane (2 marks)

  1. There is a net movement from higher to lower concentration

  2. Using a carrier/channel/intrinsic protein

  3. The proteins have a specific tertiary structure that is complementary to the glucose

  4. Binding of the glucose changes the shape of the protein so the glucose passes across the membrane

  5. It’s a passive process

4
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Explain the active transport of sodium ions through a cell surface membrane (2 marks)

  1. There is movement from a lower to higher concentration

  2. A protein carrier with a specific tertiary structure to its receptor site that is complementary to the sodium ion is required

  3. Energy/ATP is required

  4. The protein carrier requires the energy/ATP to change shape when the sodium ions bind so that they can be transported across the membrane

5
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What property allows substances to diffuse through plasma membranes?

Non-polar