A Level Biology Practice Exam

Which of the following statements is true regarding the role of membrane proteins?

1. They can only function as enzymes.

2. They perform various functions, including transport and signaling.

3. They completely block cell membranes.

4. They are present only in prokaryotic cells.

The correct answer is: They perform various functions, including transport and signaling.

Membrane proteins play diverse and vital roles in the functioning of cells, and option B accurately reflects this multifaceted nature. These proteins are embedded in or attached to the cell membrane and perform a variety of essential functions. Transport proteins are one of the key types of membrane proteins, facilitating the movement of substances across the cell membrane. This includes channel proteins that create pathways for specific ions or molecules to enter or exit the cell, and carrier proteins that change shape to ferry substances across the membrane. Additionally, membrane proteins are involved in signaling processes. Receptor proteins within the membrane can bind to specific signaling molecules, triggering a cascade of biological responses within the cell. This allows cells to communicate with each other and respond to their environment effectively. The other options do not accurately represent the functions of membrane proteins. They are not limited to enzymatic functions; rather, they encompass a wide range of roles. Membrane proteins do not completely block cell membranes; instead, they integrate into the membrane to facilitate various transport and communication processes. Lastly, membrane proteins are found in both prokaryotic and eukaryotic cells, highlighting the essential functions they serve across different life forms.