AP Biology : 2.7 Facilitated Diffusion - Exam Style questions with Answer- MCQ

AP PhysicsAP Calculus AP ChemistryAP Biology

Question

Lysosomes digest food particles brought into a cell by endocytosis. After a vesicle containing food particles fuses with a lysosome, \( $H^{+}$ ions are transported into the lysosome from the cytosol. This significantly lowers the $pH$

of the lysosome relative to the cytosol and activates the enzymes that digest the particles.

Which of the following best predicts what will happen to the lysosomal enzymes if the proteins that transport $H^{+}$

ions from the cytosol into the lysosome are damaged?

A. The lysosomal enzymes will not become active, since there will be no active transport of \( $H^{+}$ ions.

B. The lysosomal enzymes will not become active, since \( $H^{+}$ ions will diffuse out of the lysosome.

C. The lysosomal enzymes will become active, since facilitated diffusion will move \( $H^{+}$ ions into the lysosome.

D. The lysosomal enzymes will become active, since passive diffusion will move $H^{+}$ ions into the lysosome.

▶️Answer/Explanation

Ans: A
Since the $pH$ of the lysosome has to become lower than that of the cytosol, active transport is needed to move \( $H^{+}$ ions into the lysosome, against the \( $H^{+}$ ion concentration gradient, to activate the enzymes.

Question

Which of the following transport mechanisms will be affected most directly by a temporary shortage of $ATP$ molecules inside the cell?

A. The movement of water molecules through aquaporins

B. The diffusion of oxygen molecules across the plasma membrane

C. The transport of glucose molecules against a concentration gradient

D. The facilitated diffusion of \( $C a with a positive 2 charge$ ions into the cell

▶️Answer/Explanation

Ans: C
The active transport of glucose molecules against a concentration gradient requires an input of energy. Biological processes that require an input of energy typically incorporate the hydrolysis of $ATP$ , an energy-rich molecule.

Question

Some membrane proteins help maintain the concentrations of ions inside a cell by transporting the ions across the cell’s plasma membrane. Other membrane proteins form pores in the plasma membrane through which the ions can diffuse. A model showing the influence of membrane proteins on the movement of sodium (\( ${Na}^{+}$ ) and potassium (\( $K^{+}$ ) ions across a plasma membrane is presented in Figure 1.

The figure presents a bilayer plasma membrane, which separates the cytosol from the extracellular region. In the cytosol, the concentration of N a plus is low, and the concentration of K plus is high. In the extracellular region, the concentration of N a plus is high, and the concentration of K plus is low. Three membrane proteins are embedded in the plasma membrane. One protein has a channel, through which N a plus leaks into the cytolsol from the extracellular region. Another protein has a channel, through which K plus leaks out from the cytosol into the extracellular region. A third protein is a pump protein, through which Na plus is pumped out from the cytosol to the extracellular region and K plus is pumped into the cytosol from the extracellular region.

Figure 1. Section of a cell’s plasma membrane, showing ion concentrations and membrane proteins

A The \(

{Na}^{+}

concentration outside the cell will increase.

B. The \(

{Na}^{+}

concentration inside the cell will increase.

C. The \(

K^{+}

concentration inside the cell will increase.

D. The \(

K^{+}

concentration outside the cell will decrease.

▶️Answer/Explanation

Ans: B
Without $ATP$ , the \( ${Na}^{+}$ ions will continue to leak into the cell but will not be pumped out of the cell, resulting in a concentration increase inside the cell.

Question

The illustration shows the active transport of hydrogen ions through a membrane protein.

The illustration shows a cell’s plasma membrane. A membrane protein is shown with the label “A T P.” Hydrogen ions, H plus, are shown on both sides of the plasma membrane, with only a couple of ions below the membrane and many ions above the membrane. An upward pointing arrow is drawn through the channel in the center of the membrane protein to indicate the active transport of hydrogen ions from the side of the membrane with a low concentration to the side with a high concentration.

Which of the following best predicts the effect of not having

ATP

available to supply energy to this process?

A. \( $H^{+}$ ions will stop moving through the protein.
B. \( $H^{+}$ ions will move in the other direction through the protein.
C. \( $H^{+}$ ions will continue to move through the protein in the original direction but at a slower rate.
D. \( $H^{+}$ ions will begin to move through the phospholipid portion of the membrane in the original direction.

▶️Answer/Explanation

Ans: A
Metabolic energy such as $ATP$ is required for active transport of ions against a concentration gradient.

Question

The figure shows a cell membrane with an aquaporin protein embedded in it.

Which statement best describes the effect on water transport across the cell membrane if the aquaporin in the figure ceases to function?

A. Water molecules will no longer be able to move across the cell membrane.
B. Water molecules will still be able to move across the cell membrane but at a slower rate.
C. Water molecules will only be able to enter the cell by active transport.
D. Water molecules will move across the cell membrane at a faster rate without the aquaporin regulating their flow.

▶️Answer/Explanation

Ans: B
The aquaporin facilitates water passage, but water can still move across the membrane by osmosis.

AP Biology : 2.7 Facilitated Diffusion – Exam Style questions with Answer- MCQ

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