In a hypertonic solution, water flows through aquaporins embedded in the plasma membrane of the cell. This type of transport is best known as which of the following?
A.
Osmosis
B.
Diffusion
C.
Active transport
D.
Facilitated diffusion
The Correct answer and Explanation is:
Correct Answer: A. Osmosis
Explanation:
To understand why osmosis is the correct answer, it’s essential to break down the key concepts involved in cellular transport.
Osmosis refers to the movement of water across a semipermeable membrane from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration). This process occurs to balance the concentrations on both sides of the membrane, achieving equilibrium.
In the context of a hypertonic solution, the external environment surrounding the cell has a higher concentration of solutes (e.g., salt, sugar) than the cytoplasm inside the cell. Because of this imbalance, water molecules inside the cell move outwards through the aquaporins—specialized channel proteins that facilitate water transport across the plasma membrane. This outward flow of water is an attempt by the cell to reduce the concentration disparity, although it can result in cell shrinkage (crenation in red blood cells) due to the loss of water.
The other options can be ruled out based on their mechanisms:
- Diffusion (Option B) refers to the movement of molecules other than water, such as gases or solutes, from an area of high concentration to low concentration directly across the membrane or via channels. While diffusion and osmosis both involve movement from higher to lower concentrations, diffusion deals specifically with solutes, not water.
- Active transport (Option C) involves the movement of molecules against their concentration gradient, from low to high concentration, requiring energy in the form of ATP. Since osmosis is a passive process that doesn’t require energy, active transport is not the correct answer.
- Facilitated diffusion (Option D) is a passive transport mechanism where molecules move across a membrane via specific protein channels from a region of high concentration to low concentration. Like diffusion, it deals primarily with solutes rather than water.
Therefore, since the question is about the movement of water in a hypertonic solution through aquaporins, the correct term for this process is osmosis. Osmosis is a crucial physiological process, ensuring that cells maintain homeostasis by regulating water balance according to the surrounding environment.