The principal force driving movement in diffusion is the __
a. temperature
b. particle size
c. concentration gradient
d. membrane surface area
The correct answer and explanation is:
Correct Answer: c. concentration gradient
Diffusion is the passive movement of particles from an area of higher concentration to an area of lower concentration. The principal driving force behind this movement is the concentration gradient. A concentration gradient refers to the difference in the concentration of a substance between two regions. Particles naturally tend to move from areas where they are more concentrated to areas where they are less concentrated until an equilibrium is reached.
This movement occurs because particles are constantly in random motion due to their kinetic energy. When there is a higher concentration of particles in one area, the likelihood of particles moving into the less crowded area increases. Over time, this results in a net movement down the concentration gradient. Once the concentrations are equal on both sides, the net movement stops, although individual particles continue to move randomly.
Temperature, particle size, and membrane surface area can affect the rate at which diffusion occurs but they are not the driving force. For example, increasing the temperature raises the kinetic energy of particles, causing them to move faster and diffuse more quickly. Smaller particles also diffuse faster than larger ones due to lower resistance. A larger membrane surface area allows more particles to pass through at once, enhancing the diffusion rate.
However, none of these factors initiates diffusion. The fundamental cause for the movement is always the difference in concentration. Without a concentration gradient, diffusion does not occur because there is no imbalance to correct. Therefore, while other variables influence the speed and efficiency of diffusion, the concentration gradient is the essential and primary force that causes diffusion to happen in the first place.