Question

Osmosis is a special kind of diffusion, through which water diffuses across the cell membrane. The rate and direction of osmosis depends upon (a) pressure gradient (b) concentration gradient (c) both (a) and (b) (d) none of these

Short answer

The rate and direction of osmosis depend upon both the pressure gradient and the concentration gradient, which is option (c).

Step-by-step solution

Understanding Osmosis

Recognize that osmosis is the movement of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Understanding Factors Affecting Osmosis

Acknowledge that osmosis is influenced by the concentration gradient (difference in solute concentration across the membrane) and may also be affected by pressure.

Determining the Correct Factors

Since osmosis can be driven by a concentration gradient and potentially by pressure, the correct factors contributing to the rate and direction of osmosis are both the concentration and pressure gradients.

Key concepts

Diffusion in Cells

The process of diffusion is foundational to understanding how substances move within biological systems, particularly within cells. In the cell’s context, diffusion represents the spreading out of molecules from a region of higher concentration to one of lower concentration until equilibrium is reached. This movement is a result of the natural, random motion of particles.

For instance, oxygen entering a cell or waste carbon dioxide moving out occurs through diffusion. It's crucial to remember that diffusion continues until the concentration of the substances is uniform throughout the area available. This process does not require external energy because it involves the movement down the concentration gradient, which is a form of potential energy inherent in the system.

Concentration Gradient

A concentration gradient is essentially a difference in the concentration of a substance across a space. In biological systems, this space is often across a cell membrane. The gradient represents a form of potential energy that drives the diffusion process.

Molecules will naturally move from an area of higher concentration, where they are more likely to bump into each other, to an area of lower concentration, where there is more space to spread out. This movement continues until the concentration on both sides of the membrane is equal. Osmosis, a type of diffusion specific to water molecules, is likewise influenced by these concentration differences. By comprehending the gradient, students can better predict how substances, including water, will move in biological systems.

Pressure Gradient

Pressure gradients play a critical role in the movement of substances, particularly in the context of osmosis. Just as with concentration gradients, pressure gradients involve a difference in pressure across a space. A higher pressure on one side of a cell membrane can force molecules to move to the lower pressure side, akin to how air moves from a high-pressure weather system into a low-pressure system.

Osmosis can be influenced by the turgor pressure within plant cells, which is the pressure of the cell contents against the cell wall. If external pressure is applied, it can counteract the osmotic movement of water, changing the rate and direction of flow. Understanding pressure gradients in addition to concentration gradients gives a more complete picture of the factors affecting osmosis and the behavior of cells in various environments.