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Membranes and transport

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Which component provides a selective hydrophilic passage for an ion?

  1. A suitable membrane channel protein.
  2. A peripheral protein lying on the surface of the bilayer.
  3. The non-polar fatty-acid tails alone.
  4. An unattached carbohydrate molecule outside the cell.
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A suitable membrane channel protein.

Its hydrophilic passage allows an otherwise restricted substance to cross.

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Which is a benefit of an internal membrane?

  1. Maintaining a compartment with conditions different from the cytosol.
  2. Stopping exchange between the compartment and the cytosol.
  3. Keeping the conditions in each compartment the same as in the cytosol around it.
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Maintaining a compartment with conditions different from the cytosol.

Selective boundaries support different local reaction conditions.

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Which observation fits facilitated diffusion?

  1. A vesicle engulfs a bacterium.
  2. A carrier pumps ions against their gradient, using ATP.
  3. A specific carrier moves a polar solute down its gradient.
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A specific carrier moves a polar solute down its gradient.

Protein-mediated movement down a gradient can be passive.

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Uptake of a sugar by cells increases with its external concentration, then levels off. Uptake is unaffected by a respiratory inhibitor. Which mechanism is best supported?

  1. Endocytosis into vesicles
  2. Simple diffusion through the phospholipid bilayer
  3. Active transport by carrier proteins
  4. Facilitated diffusion through carrier proteins
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Facilitated diffusion through carrier proteins

The plateau shows a limited number of carriers; no effect of the inhibitor shows no ATP is needed.

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Which extra feature is needed to explain sustained net uptake against a gradient?

  1. Energy coupling to a suitable transport protein.
  2. Random motion only.
  3. A larger concentration gradient in the opposing direction, with no energy source.
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Energy coupling to a suitable transport protein.

This can drive the uphill movement.

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Which process releases a secreted protein from a vesicle?

  1. Exocytosis.
  2. Osmosis.
  3. Simple diffusion through lipid tails.
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Exocytosis.

The vesicle fuses with the surface membrane and opens to the exterior.

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Which statement about exocytosis is NOT correct?

  1. It can release enzymes and hormones
  2. It requires energy from ATP
  3. The vesicle contents pass through a channel protein
  4. The vesicle membrane joins the cell membrane
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The vesicle contents pass through a channel protein

In exocytosis the vesicle membrane fuses with the cell membrane; contents are not passed through a channel.

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Question 1 of 7

Explain the mosaic

4 marks

Explain how phospholipids, proteins, glycolipids, glycoproteins and cholesterol contribute to cell membrane function. [4]

Assign a distinct role to every named component.

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