Question

The cellular process diffusion does not require cellular ________________ to reach equilibrium. Similarly, ________________uses a selectively permeable membrane to reach equilibrium. This Membrane allows _____________to pass through, but not soluble particles or molecules. It too does Not require cellular energy. When molecules cannot move through a cell membrane passively, the Cell uses a process called_____________. This process uses_______________ found in the cells Membrane to pass particles and reach equilibrium.

Answer 1

In a solution, particles move constantly. They collide with one another and tend to spread out randomly. As a result, the particles tend to move from an area where they are more concentrated to an area where they are less concentrated, a process known as diffusion (dih-FYOO-zhun). When the concentration of the solute is the same throughout a system, the system has reached equilibrium.

What do diffusion and equilibrium have to do with cell membranes? Suppose a substance is present in unequal concentrations on either side of a cell membrane, as shown in the figure at right. If the substance can cross the cell membrane, its particles will tend to move toward the area where it is less concentrated until equilibrium is reached. At that point, the concentration of the substance on both sides of the cell membrane will be the same.

Because diffusion depends upon random particle movements, substances diffuse across membranes without requiring the cell to use energy. Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions. However, because almost equal numbers of particles move in each direction, there is no further change in concentration.