Martha Campos, age 15, of Fargo, N.D.. for her question:
WHAT IS THE DIFFERENCE BETWEEN ABSORPTION AND ADSORPTION?
Absorption and adsorption are the processes by which substances gather up matter or energy or both.
Absorption is the gathering of either matter or energy in such a way that it becomes fairly evenly distributed throughout the absorbing material.
Adsorption is the gathering of matter only. The matter collects on the surface of the adsorbing material. It does not enter the interior.
There are many familiar examples of absorption. Heavy drapes, for example, absorb sound energy. The sound waves make the fibers in the drapes vibrate and rub together. Friction turns the sound energy into heat so the sound cannot be reflected as an echo.
Colored objects and filters absorb light energy. The light energy makes certain electrons in the atoms of the coloring substance more energetic. Less light and different colors remain after the process.
Dry earth absorbs water by capillarity.
The water in a lake absorbs oxygen by dissolving it.
Usually only solid material can adsorb another substance. But the adsorbed matter can be the molecules of a liquid or a gas, or tiny particles of a solid.
The process of adsorption is often highly selective. This makes it useful for purifyin.kj liquids and gases.
Adsorption by a large collection of small particles, as in a charcoal filter, is often accomplished by the adsorption of molecules on the surface of each particle. Silica gel adsorbs water molecules from moist air and holds them on the surface of each grain. Adsorption releases heat called heat of adsorption.
Adsorbed molecules may be held either weakly or strongly.
Holding forces are weak when physical attraction holds the molecules to the adsorbing surface. This process is called physiosorption.
Strong holding forces exist when the adsorbed molecules are united chemically to the surface. This process is called chemisorption.
In chemisorption, the adsorbed molecules form only a single layer. But in physiosorption, they may form layers several molecules deep.
Plants must have a continuous supply of water. Each individual plant cell contains a large amount of water. Without this water, the cells could not carry on the many processes that take place within a plant. Water also carries important materials from one part of a plant to another.
Most water enters a plant through the roots. Tiny hair roots absorb moisture and minerals from the soil by a process called osmosis.