BASIC BIOLOGY & METHODS of SCIENCE

Introduces fundamental biological mechan-
isms that are basic to an understanding of
how organisms live and function. Presents
some of the fundamental intellectual, phys-
ical & conceptual tools of scientific study.

pH CONCEPT, OSMOSIS and DIFFUSION
Vital cellular processes and the underlying biochemical basis. 2 programs, 30 slides, guides.
EPSS-0492X SLIDES
$59.95

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SAVE OVER $9.00 ON 2 SLIDE SET BUNDLE ORDER EP #SS-0492X.....$59.95
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THE pH CONCEPT Slides order #SS-0960S .........$34.95

The biochemical reactions that are necessary for life are profoundly influenced
by the pH of cellular solutions. This program discusses the chemical nature and
measurement of pH, its biological importance, as well as some aspects of its
homeostatic regulation. 15 frames and guide. (Filmstrip order SS-0960F........$15.00.)

CONTENT SAMPLE: 13. Extreme pH changes decrease the solubility of cellular
proteins to the extent that they precipitate into a formless soup. This would destroy both cell
structure and function. Living systems must therefore avoid pH fluctuations of their intra- and
intercellular fluids. This is a formidable task when one considers the great array of acids and
bases that are assimilated by living systems, not to mention the acidic and basic byproducts of
cellular metabolism. pH can be maintained within a constant range in living systems due to
buffers.

A buffer is a solution of a weak acid or a weak base and its corresponding salt that
keeps pH constant under diverse conditions. Weak acids and bases are those which dissociate
very little in solution (as opposed to strong acids and bases like HCL and NaOH which
dissociate completely). The weak acid or base is in equilibrium with its dissociated salts. By
the law of mass action, an increase in the concentration of either reactant or product forces the
reaction in the opposite direction, thereby maintaining the original equilibrium.

Weak acids and bases can therefore serve as reservoirs that can react with any extra
hydrogen or hydroxide ions that may enter the medium. For example, if excess acid is added to
a buffer solution of a weak acid and its salt (left), the introduced hydrogen ions initially increase
the pH (middle). But as the weak acid's anions (negatively charged ions) take up the extra H+
the original pH becomes reinstated (right). If a base is added, the free protons combine to form
additional salt. In both cases, the ratio of [buffer acid] to [buffer salt] remains constant; and so
does the pH.
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OSMOSIS & DIFFUSION Slides order #SS-0490S.........$34.95

The basic laws and results of these cellular phenomena are treated so as to
instill in the student both an objective and intuitive understanding of these processes on
which life depends. 15 frames and guide. (Filmstrip order SS-0490F.......$15.00.)

CONTENT SAMPLE: 10. The mechanism of osmosis is simple; osmosis is a special
kind of diffusion. The salt in the solution side is in higher concentration than on the other side of
the membrane. Salt, however, cannot pass through the membrane. The water, which is lower in
concentration on the side that contains solute, can diffuse from the pore side to the other side.
This diffusion (osmosis) produces the observed change in water levels; the water tries to equalize
its concentration on both sides of the membrane.
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0490_04a Diffusion. graphic by Educational Images Ltd.

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