Transcript Chapter 3: Water and the Fitness of the Environment

Topic 2: The Chemistry of Life
Chapter 3: Water and the
Fitness of the Environment
IB HL Biology
Douglas County HS
Mr. Spoor
Essential Elements of LifeTopic 3.1.1
• About 25 of the 92 elements are essential to life
• Carbon, hydrogen, oxygen, and nitrogen make
up 96% of living matter
• Most of the remaining 4% consists of calcium,
phosphorus, potassium, and sulfur
• Trace elements are those required by an organism
in minute quantities, such as iodine.
Other Biologically Important Elements
and their functions- Topics 3.1.2 & 3.1.3
Calcium (Ca): Formation of bones and shells in animals,
involved with muscle contraction and neuron activity in animals.
Phosphorous (P): Forms energy storing compounds ATP,
Nucleotides (A,T, G, C, U), and membrane building molecules
(phospholipids).
Sulfur (S): amino acids and protein structure
Sodium (Na): Neuron activity, water balance, and membrane
transport
Potassium (K): membrane transport and muscle activity
Iron (Fe): oxygen transport of red blood cells as a component
of hemoglobin.
Magnesium (Mg): light activated atom component of
chlorophyll molecules.
This is important!
Overview: The Molecule That Supports
All of Life
Water is the biological medium on Earth
All living organisms require water more than any other
substance
Most cells are surrounded by water, and cells themselves
are about 70–95% water
The abundance of water is the main reason the Earth is
habitable
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Did you know that…
Water is the most common
chemical compound in the world
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Contributes to global warming and
the greenhouse effect?
Is found in large quantities in tumors
and other cancers?
Was found in significant quantities
in the levees breached during
Hurricane Katrina?
Is ingested by cows in large
quantities, leading to increased milk
production?
Properties of Water
Let’s look at the major
properties of water and how
they are important to living
things
1. Polar Properties
Water is Polar
Because of the uneven
balance of extra electrons
possessed by oxygen,
water has a slightly
negative charge
The hydrogen end is
slightly positive
Hydrogen Bonding
Water has hydrogen
bonding between
molecules.
This causes the
molecules to “stick”
together.
Each molecule can
attract 4 other water
molecules.
This gives water some
of its unique
characteristics.
Important
Topic 3.1.4- Draw and label water
molecules to show their polarity and
hydrogen bond formation (add the
charges and bond types)
2. Solvent Properties
The polar properties of
water make it a good
solvent for:
Polar molecules (e.g.
sugars and alcohols)
These form hydrogen
bonds with the water
molecules
Ionic compounds
(e.g. salts, acids and
bases)
These dissociate into
their component ions
Solvent properties and life
Water is a very important transport
medium for living organisms, because
of its solvent properties and...
Water is also an important medium for
biochemical reactions because it
remains a liquid over a large range of
temperatures
3. Cohesive Properties
a. Water has Cohesion:
-Water molecules stick to
each other due to
hydrogen bonding
Important in fluid
transport of plants, such
as tall trees
The water forms a tall
column that rarely breaks
b. Surface Tension
Surface tension is a
measure of how hard it
is to break the surface
of a liquid
This is strong enough
for some organisms to
be supported
Surface tension is
related to cohesion
c. Adhesion
Water also exhibits
adhesion- an attraction
to other substances.
Together with
cohesion, this helps
water reach the tops of
the tallest trees.
Giant red wood
Sequoiadendron giganteum
N. California
Fig. 3-3
Adhesion
Water-conducting
cells
Direction
of water
movement
Cohesion
150 µm
4. Thermal Properties
 a. Water has a very high thermal capacity
(4.2 J°C-1 g-1) and a high heat of
vaporization.
 b. Heat of vaporization is the heat a liquid
must absorb for 1 g to be converted to gas.
 Water absorbs heat from warmer air and
releases stored heat to cooler air
 Water can absorb or release a large amount
of heat with only a slight change in its own
temperature
High Specific Heat
c. The specific heat of a
substance is the amount of
heat that must be
absorbed or lost for 1 g of
that substance to change
its temperature by 1ºC
The specific heat of water
is 1 cal/g/ºC
Water resists changing its
temperature because of its
high specific heat
High Heat Capacity and Life
Blood acts as a transport
medium for heat in living things
Since blood is made up of
mostly water, it can carry
warmth to cooler locations in
the body
Very low or very high
temperatures may damage
enzymes or slow down
important chemical reactions
Because the human body is
mostly water, a sunbather can
absorb a lot of heat energy
without sending her/his body
temperature soaring
Water is a great coolant
d. Evaporative cooling
helps to moderate
temperatures in bodies of
water as well as in the
bodies of land organisms.
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This is why sweating cools
you off.
Transpiration in plants also
acts as a coolant
This helps keep global
temperatures in check.
African elephants (Loxodonta africana) bathing
© Shirley Burchill 2007
e. High Boiling Point
Water’s boiling
point is very high
(100 C) compared
to other liquids
A large amount of
energy is required
to break the
hydrogen bonds
between water
molecules
5. Other properties: Density
Less dense as solid than liquid due to
hydrogen bonding
Crystalline lattice keeps molecules at a
distance
Density
This allows ice to float atop
bodies of water, serving as an
insulator for life below
Other properties: Transparency
Water is transparent and translucent
Allows light to penetrate bodies of water so
producers can photosynthesize
Hydrophilic and Hydrophobic
Substances
A hydrophilic substance is one that
has an affinity for water
A hydrophobic substance is one that
does not have an affinity for water
Oil molecules are hydrophobic because
they have relatively nonpolar bonds