A Level Biology Practice Exam

What do channel proteins facilitate in cellular membranes?

1. Cell division

2. Intercellular communication

3. Transport of hydrophilic substances

4. Production of energy

The correct answer is: Transport of hydrophilic substances

Channel proteins primarily facilitate the transport of hydrophilic substances across cellular membranes. These proteins form specific channels through which polar molecules and ions can pass. Since the lipid bilayer of cell membranes is hydrophobic, hydrophilic substances cannot diffuse freely through it. Channel proteins provide a hydrophilic pathway that allows these substances, such as water, ions, and other small polar molecules, to enter or exit the cell efficiently. This transport mechanism is crucial for maintaining homeostasis within the cell and allowing it to respond to environmental changes. For instance, ion channels enable the movement of essential ions like sodium, potassium, calcium, and chloride, which are vital for various cellular functions, including nerve impulse transmission and muscle contraction. The specificity of channel proteins means that they can also be gated, opening or closing in response to certain signals, thus regulating the flow of substances based on the cell's needs. In summary, the role of channel proteins is central to the facilitated diffusion process, ensuring that vital hydrophilic substances traverse the cell membrane in an efficient and controlled manner.