AP Biology : 2.3 Plasma Membranes - Exam Style questions with Answer- MCQ

Question

Figure 1. Testosterone movement across the cellular membrane

Testosterone is a small steroid hormone that is important in cell signaling. Which of the following describes where testosterone enters a cell and why it is able to cross at that point?

A. 1, testosterone is nonpolar and can diffuse through the membrane.

B. 2, testosterone covalently binds to a surface protein and transports into the cell.

C. 3, testosterone dissolves in water and flows through the channel.

D. 4, testosterone is filtered out of the extracellular fluid and taken into the cell by endocytosis.

Answer/Explanation

Ans: A
Steroids such as testosterone are hydrophobic lipids. Therefore, testosterone can cross the hydrophobic inner region of the phospholipid bilayer.

Question

The figure shows a representation of a protein embedded in a cell membrane. The numbers indicate different structural regions of the protein.

Based on the figure, which of the following statements best describes the relationship between regions 1 and 2 of the protein?
A. Region 1 is hydrophilic because it interacts with the interior of the membrane, whereas region 2 is hydrophobic because it interacts with an aqueous environment.
B. Region 1 is hydrophilic because it interacts with an aqueous environment, whereas region 2 is hydrophobic because it interacts with the interior of the membrane.

C. Region 1 is hydrophobic because it interacts with the interior of the membrane, whereas region 2 is hydrophilic because it interacts with an aqueous environment.
D. Region 1 is hydrophobic because it interacts with an aqueous environment, whereas region 2 is hydrophilic because it interacts with the interior of the membrane.

Answer/Explanation

Ans: B
A cell membrane is a phospholipid bilayer that separates one aqueous environment from another. The interior of a phospholipid bilayer is a hydrophobic environment. Because region 1 interacts with the aqueous environment on one side of the phospholipid bilayer, it is most likely hydrophilic. Because region 2 interacts with the interior of the phospholipid bilayer, it is most likely hydrophobic.

Question

Cholesterol is a naturally occurring substance that helps regulate the fluidity of a cell’s plasma membrane. A cholesterol molecule can be represented as having a polar head and a nonpolar region, as shown in the figure.

Which of the following models shows how cholesterol molecules most likely interact with the phospholipid bilayer of a cell’s plasma membrane?

▶️Answer/Explanation

Ans: D
The model correctly shows the polar heads of the cholesterol molecules interacting with the polar heads of the phospholipids. Also, the model correctly shows the nonpolar regions of the cholesterol molecules interacting with the hydrophobic interior of the phospholipid bilayer.

AP Biology : 2.3 Plasma Membranes – Exam Style questions with Answer- MCQ

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