Chapter 7, Problem 36A

Summary Introduction

To determine: The factor which does not affect the rate of diffusion

Introduction:

Diffusion can be defined as the movement of a substance from an area of high concentration to an area of low concentration. Diffusion happens in liquids and gases because their particles move randomly from place to place. The diffusion does not involve energy expenditure as it occurs along the concentration gradient hence it’s a passive process.

Answer to Problem 36A

The factor that does not affect the rate of diffusion is conductivity. Other factors such as pressure, concentration and temperature affect the rate of diffusion.

Explanation of Solution

Factors on which rate of diffusion depends are:

Extent of the concentration gradient: The greater the difference in concentration, the more rapid the diffusion.

Mass of the molecules diffusing: Heavier molecules move more slowly; therefore, they diffuse more slowly.

Temperature: Higher temperatures increase the energy and therefore the movement of the molecules, increasing the rate of diffusion.

Solvent density: As the density of a solvent increases, the rate of diffusion decreases. The molecules slow down because they have a more difficult time getting through the denser medium. If the medium is less dense, diffusion increases.

Solubility: Nonpolar or lipid-soluble materials pass through plasma membranes more easily than polar materials, allowing a faster rate of diffusion.

Surface area and thickness of the plasma membrane: Increased surface area increases the rate of diffusion, whereas a thicker membrane reduces it.

Distance travelled: The greater the distance that a substance must travel, the slower the rate of diffusion.