Section 2c
The study of the chemical
composition and reactions of
living matter.
• Organic compounds
– Contain carbon, are covalently
bonded, and are often large
• Inorganic compounds
– All other chemicals in the body
– Do not contain carbon
– Water, salts, and many acids and
• We will go over
– Water
– Salts
– Acids
– Bases
– pH
– Buffers
Most abundant and
important inorganic
compound in living material.
Makes up 60% - 80% of the
volume of most living cells.
Properties of Water
• High heat capacity
– absorbs and releases large amounts of
heat before changing temperature
– This prevents sudden changes in body
temperature cased by external factors
like sun or wind or internal factors like
heat released during vigorous muscle
– As a part of blood, water redistributes
heat among body tissues, ensuring
temperature homeostasis
Properties of Water
• High heat of vaporization
– changing from a liquid to a gas
requires large amounts of heat
– As we sweat, perspiration (mostly
water) evaporates from our skin
removing large amounts of heat
– This is a very efficient cooling
mechanism for our bodies!
Properties of Water
• Polar solvent properties
– Water is often called the
universal solvent
– dissolves ionic substances
– forms hydration layers around
large charged molecules
– serves as the body’s major
transport medium
Properties of Water
• Reactivity
– an important part of hydrolysis and
dehydration synthesis reactions
– Food is digested to their building
blocks by adding a water molecule to
each bond - Hydrolysis reactions
– Carbohydrates and proteins are
synthesized from smaller molecules
by removing a water molecule for each
bond formed – dehydration synthesis
Properties of Water
• Cushioning
– resilient cushion around certain
body organs
– Helps protect organs from
physical trauma
– Cerebrospinal fluid surrounding
the brain is an example
• Inorganic compounds
• Contain cations other than H+
and anions other than OH–
• Are electrolytes; they conduct
electrical currents
• Maintaining proper ionic balance
in our body fluids is one the
most crucial homeostatic roles
of the kidneys.
• When this balance is severely
disturbed, virtually nothing in
the body works.
Acids and
Acids and Bases are also
Conduct electrical current
• Tastes sour
• Dissolves many metals
• Acids release H+ and are
therefore proton donors
HCl  H+ + Cl –
Acids are proton donors!
• Tastes bitter
• Feel slippery
• Bases release OH– and are
proton acceptors
NaOH  Na+ + OH–
Bases are proton acceptors!
Acid-Base Concentration
• Acidic solutions have higher H+
concentration and therefore a
lower pH
• Alkaline (basic) solutions have
lower H+ concentration and
therefore a higher pH
• Neutral solutions have equal H+
and OH– concentrations
Acid-Base Concentration (pH)
• Acidic: pH 0–6.99
• Basic: pH 7.01–14
• Neutral: pH 7.00
Figure 2.12
• When acids and bases are mixed,
they react with each other in a
displacement reaction to form
water and a salt.
HCl + NaOH -> NaCl + H2O
• Systems that resist abrupt and
large swings in the pH of body
fluids are buffering systems
• If blood pH varies from the narrow
range of 7.35 – 7.45 by more than a
few tenths, it can be fatal!
• Homeostasis of acid-base balance is
regulated by the kidneys and lungs
and by chemical systems called
Buffer systems
• Carbonic acid-bicarbonate system is
a very important chemical blood
– Carbonic acid dissociates
reversibly, releasing bicarbonate
ions and protons
– The chemical equilibrium between
carbonic acid and bicarbonate
resists pH changes in the blood
Next time!

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