Sci Paper Ref
2
Biological Principles and Processes Second Edition Claude A. Villee Vincent G. Dethier 1976 W. B. Saunders Company Diffusion may be defined as the movement of molecules from a region of high concentration to one of lower concentration brought about by their kinetic energy of the molecules. The rate of diffusion is a function of the size of the molecule and the temperature. Even the molecules that make up a solid are constantly in motion. The chief difference between the three states of matter – solid, liquid and gas – is simply the freedom of movement of the molecules present. The molecules of a solid are relatively closely packed and the forces of attraction allow them to vibrate but not to move around. In the liquid state the molecules are further apart, the intermolecular forces are weaker, and the molecules move about with considerable freedom. Finally, in the gaseous state, the molecules are so far apart that inter molecular forces and molecular movement is restricted only by external barriers. When a drop of water is examined under the microscope, the motion of the water molecules is not evident. However, if we add a drop of India ink (which contains fine particles of carbon) we can observe under the microscope the motion the motion of carbon particles. Each carbon particle is constantly being bumped by water molecules, and the recoil from these bumps moves the carbon particle in an aimless, zigzag path. This motion of small particles is termed Brownian movement after Robert Brown, an English botanist, who first observed it when he looked through the microscope at some tiny pollen grains in a drop of water.
description
bio
Transcript of Sci Paper Ref
Biological Principles and Processes Second Edition
Claude A. Villee
Vincent G. Dethier
1976 W. B. Saunders Company
Diffusion may be defined as the movement of molecules from a region of high concentration to one of lower concentration brought about by their kinetic energy of the molecules. The rate of diffusion is a function of the size of the molecule and the temperature. Even the molecules that make up a solid are constantly in motion. The chief difference between the three states of matter – solid, liquid and gas – is simply the freedom of movement of the molecules present. The molecules of a solid are relatively closely packed and the forces of attraction allow them to vibrate but not to move around. In the liquid state the molecules are further apart, the intermolecular forces are weaker, and the molecules move about with considerable freedom. Finally, in the gaseous state, the molecules are so far apart that inter molecular forces and molecular movement is restricted only by external barriers.
When a drop of water is examined under the microscope, the motion of the water molecules is not evident. However, if we add a drop of India ink (which contains fine particles of carbon) we can observe under the microscope the motion the motion of carbon particles. Each carbon particle is constantly being bumped by water molecules, and the recoil from these bumps moves the carbon particle in an aimless, zigzag path. This motion of small particles is termed Brownian movement after Robert Brown, an English botanist, who first observed it when he looked through the microscope at some tiny pollen grains in a drop of water. Brownian movement provides a model of how diffusing particles move.
In the process of diffusion, each individual molecule moves in a straight line until it bumps into something – another molecule or the side of the container – then it rebounds and moves in another direction. Individual molecules may move at a rate of several hundred meters per second, but each molecule can go only a fraction of a nanometer before bumping into another molecule and rebounding. Thus the progress of any given molecule in a straight line is quite slow. The molecules continue to move even when they have become uniformly distributed throughout a given space
