Cell Transport Review

Which of the following most accurately describes the movement of substances across the lipid region of the cell membrane?

• Uncharged molecules like H_2​O cannot dissolve across the lipid region of the cell membrane.

• Gases such as N₂, O₂, and CO₂ can freely dissolve across the lipid region of the cell membrane.

• Small hydrophobic molecules require embedded transport proteins to dissolve across the lipid region of the cell membrane.

• Monosaccharides can freely dissolve across the lipid region of the cell membrane.

Which of the following statements best describes the selective permeability of the cell membrane?

• The cell membrane regulates the transport of intracellular substances out of, but not into the cell.

• The cell membrane regulates the transport of extracellular substances into, but not out of the cell.

• The cell membrane regulates the transport of specific substances into and out of the cell.

• The cell membrane regulates the transport of all substances into and out of the cell.

Which of the following best describes the permeability of the cell wall?

• The cell wall is a semipermeable structural boundary that only allows water to enter the internal environment.

• The cell wall is an impermeable structural boundary that prevents all substances from entering the internal environment.

• The cell wall is a semipermeable structural boundary that allows some substances to enter the internal environment.

• The cell wall is a permeable structural boundary that allows all substances to enter the internal environment.

The model below depicts the movement of several ions across a cell membrane. For each ion, the relative concentration on each side of the membrane is shown.

Which of the following statements accurately describes one of the movements shown in the model?

• H+ movement out of the cell does not require an input of energy.

• K+ moves out of the cell by passive transport.

• Cl− moves out of the cell by passive transport.

• K+ movement into the cell does not require an input of energy.

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The model below depicts the movement of several ions and molecules across a cell membrane. For each ion or molecule, the relative concentration on each side of the membrane is shown.

Which of the following statements accurately describes one of the movements shown in the model?

• O₂ is transported into the cell by active transport.

• K+ movement out of the cell requires ATP hydrolysis.

• Ca²⁺ is transported out of the cell by active transport.

• Glucose movement into the cell requires ATP hydrolysis.

If ATP hydrolysis is inhibited, which of the following types of movement across a cell membrane would likely also be inhibited?

• Passage of water through aquaporins

• Facilitated diffusion of a substance through channel proteins

• Movement of an ion against its concentration gradient

• Movement of carbon dioxide molecules down their concentration gradient

The movement of ions across a cell membrane can generate a membrane potential, or a voltage difference, across the membrane.

In neurons, this occurs when sodium-potassium pumps, Na+ / K+, ATPases, transport sodium ions (Na+) and potassium ions (K+) across the cell membrane against their concentration gradients. The action of these pumps, combined with the diffusion of certain ions through protein channels in the membrane, results in a resting membrane potential of approximately −70mV with respect to the inside of the cell.

Which of the following diagrams best represents the resting membrane potential of a neuron?

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An action potential occurs when a neuron sends an electrical signal down its axon. When at rest, the neuron’s plasma membrane helps maintain a concentration gradient of sodium ions (Na+) between the neuron’s cytoplasm and the extracellular fluid. During an action potential, Na+ moves down this gradient, passing from the extracellular space into the cytoplasm of the neuron.

Which of the following is the most likely mechanism by which Na+ moves across the plasma membrane of a neuron during an action potential?

• Na+ lows through aquaporins

• Na+ directly diffuses through the membrane bilayer.

• Na+ is transported through transmembrane ATPases.

• Na+ passes through membrane channel proteins.

The model below shows how glucose, sodium ions (Na+), and potassium ions (K+) move between the intestinal lumen, an epithelial cell, and the blood in the small intestine. The relative concentrations of glucose, Na+, and

K+ inside and outside the epithelial cell are indicated.

Based on the model, which of the following movements does not require an input of energy?

• K+ moving out of the blood into an epithelial cell

• glucose moving out of an epithelial cell into the blood

• glucose moving out of the intestinal lumen into an epithelial cell

• Na+ moving out of an epithelial cell into the blood

Which of the following is true about the transportation of substances across the lipid region of the cell membrane?

• Polysaccharides can freely dissolve across the lipid region of the cell membrane.

• Small nonpolar molecules can freely dissolve across the lipid region of the cell membrane.

• Ions can freely dissolve across the lipid region of the cell membrane.

• Gases such as N2, O2, and CO2 require embedded transport proteins to dissolve across the lipid region of the cell membrane.