“…beneath the clothes, we find a man... and beneath
the man we find... his... nucleus.”-Nacho Libre
Reference Text - Modern Biology
Chapter 3 - 1 / pgs. 48 - 51
Modern Biology
pgs. 40 - 42
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The chemistry of living things involves
the study of solutions
The chemical reactions of life occur mostly
in aqueous solutions!
A solution is a mixture in which one or more
substances are uniformly mixed with another.
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Solute: the substance dissolved in the solution.
Solvent: The substance in which the solute is dissolved.
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Aqueous Solution:
◦ water is the solvent
◦ Very important to living things – most chemical
reaction involve solutes dissolved in water
Examples:
 Marine Microorganisms spend their entire lives in salt
water – an aqueous solution
 Plant get the nutrients they need through aqueous
solutions found in moist soil
 Cells exist in an aqueous solution
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An important aspect of a living system is its
degree of acidity or alkalinity – pH !
pH is determined by the amount of
Hydrogen - H+ or hydronium - H3O+ ions
dissolved in a solution.
Water spontaneously DISSOCIATES or
“breaks apart ” to form ions (charged particles).
The “free” H+ ion can react with another
H2O molecule forming a “Hydronium ion”.

If a compound “ionizes” or
dissociated when dissolved in
water and produces:
◦ … a greater number of H+ or
H3O+ ions, the solution is said to
be an acidic solution, or ACID.
◦ … a greater number of
hydroxide OH- ions, it is said to
be an alkaline solution, or
BASIC.
Scientists have developed a scale to measure
the relative concentration of hydronium ions
and hydroxide ions in a solution:
From:
0 - 14
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pH 0-6
Taste sour
Corrosive (burn things, eat away at materials
◦ *Acid rain can corrode stone and make bodies of
water uninhabitable for life.
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Example: lemon juice, coke,
vinegar, stomach acid.
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pH 8-14
Bitter taste
Feels slippery
Corrosive
◦ *Also called alkaline*
Example: ammonia, milk of magnesia, egg white
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If the number of hydroxide ions equals the
number of hydronium ions
Neither acidic or basic
pH = 7.0
Example: PURE
water
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The control of pH in organisms is very
important - Complex buffering systems
maintain the pH values of your body’s many
fluids at normal levels - Neutralization !
Produced naturally by the body to maintain
HOMEOSTASIS!
◦ Rolaids, Mylanta and Pepcid are all stomach acid neutralizers.
◦ Buffered aspirin helps reduce heartburn and upset stomach
that aspirin may cause.