3.8–3.11: Molecules move across membranes in several ways.

Cells must import food molecules and other necessary materials from outside the cell and export metabolic waste and molecules produced for use elsewhere.

Question 3.19

Hydrophobic molecules can pass freely through the plasma membrane, but ions and polar molecules are impeded by the hydrophobic core. For this reason, plasma membranes can be considered:

  • a) partially permeable.
  • b) impermeable.
  • c) hydrophobic.
  • d) hydrophilic.
  • e) None of these terms properly describe plasma membranes.

Question 3.20

Drugs called beta-blockers do all of the following except:

  • a) reduce high blood pressure.
  • b) block signaling through adrenaline receptors.
  • c) reduce outward symptoms of anxiety.
  • d) bind to the cytoplasmic side of a receptor protein.
  • e) reduce the effects of adrenaline on the heart.

Question 3.21

Cellular “fingerprints”:

  • a) are exposed on the cytoplasmic side of the membrane.
  • b) are made from cholesterol.
  • c) are “erased” by HIV.
  • d) can help the immune system distinguish “self” from “non-self.”
  • e) All of the above are correct.

Question 3.22

The movement of molecules across a membrane from an area of high concentration to one of low concentration is best described as:

  • a) active transport.
  • b) inactivated transport.
  • c) passive transport.
  • d) channel-mediated diffusion.
  • e) electron transport.

Question 3.23

The transport of water across a membrane from a solution of lower solute concentration to a solution of higher solute concentration is best described as:

  • a) osmosis.
  • b) facilitated diffusion.
  • c) receptor-mediated transport.
  • d) active transport.
  • e) general diffusion.

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