Water is essential for life due to its unique properties arising from hydrogen bonding between polar water molecules. Water's polarity allows it to dissolve many other polar substances and ions, acting as a universal solvent and transport medium in organisms. Water's high specific heat capacity and heat of vaporization enable important thermal regulation processes. In blood, glucose, amino acids, and ions are carried in the plasma due to their polarity, while fats and cholesterol require transport in lipoprotein complexes due to their nonpolar nature. Oxygen is only slightly soluble in water alone, and is mainly transported bound to hemoglobin in red blood cells. The document discusses these topics through examples and comparisons to methane.

1. 2.2 Water
Essential idea: Water is the medium of life.

2. Understandings, Applications and Skills
Statement Guidance
2.2 U.1 Water molecules are polar and hydrogen
bonds form between them.
2.2 U.2 Hydrogen bonding and dipolarity explain
the cohesive, adhesive, thermal and
solvent properties of water.
Students should know at least one
example of a benefit to living
organisms of each property of water.
Transparency of water and maximum
density at 4°C do not need to be
included.
2.2 U.3 Substances can be hydrophilic or
hydrophobic.
2.2 A.1 Comparison of the thermal properties of
water with those of methane.
Comparison of the thermal properties
of water and methane assists in the
understanding of the significance of
hydrogen bonding in water.
2.2 A.2 Use of water as a coolant in sweat.
2.2 A.3 Modes of transport of glucose, amino
acids, cholesterol, fats, oxygen and sodium
chloride in blood in relation to their
solubility in water.

3. • A water molecule consists of an oxygen
atom covalently bound to two hydrogen
atoms
• Since O is more electronegative than H,
an unequal sharing of electrons occurs
• This creates a polar covalent
bond, with H having a partial positive
charge and O having a partial negative
charge
• The partial + charge is attracted to the
partial – charge creating an
intermolecular attraction between the
water molecules called a “Hydrogen
bond.”
• H-bonds are the strongest of the
intermolecular bonding, but is still
considered a weak bond; however since
there are so many H2O molecules they
give water its unique properties and
make it essential to life on this planet
2.2 U.1 Water molecules are polar and hydrogen bonds form between
them.

4. 2.2 U.2 Hydrogen bonding and dipolarity explain the cohesive, adhesive,
thermal and solvent properties of water.
Thermal Property
• Water has a high specific heat
capacity (amount of energy needed to
raise temperature of a substance by a
certain temperature level). Basically,
water can absorb a lot of heat and give
off a lot of heat without drastically
changing the temperature of water.
• Water’s high specific heat capacity results
from the extensive hydrogen bonding
between the water molecules.
• Water also has a high latent heat of
vaporization which means it takes a lot of
heat to evaporate water from a liquid to
a vapor. This is very important as a
cooling mechanism for humans. As we
sweat, the water droplets absorb heat
from our skin causing the water to
evaporate and our bodies to cool down.
http://community.thefoundry.co.uk/discussion/topic.aspx?f=9&t=77728

5. 2.2 A.2 Use of water as a coolant in sweat.

6. 2.2 A.1 Comparison of the thermal properties of water with those
of methane.
Methane
• waste product of
anaerobic respiration in
certain prokaryotes living
in anaerobic conditions
• Methane can be used as a
fuel
• If present in the
atmosphere it contributes
to the greenhouse effect.
Methane Water
Formula CH4 H2O
Molecular mass 16 18
Bonding Single covalent
Polarity nonpolar polar
Density (g cm-3) 0.46 1
Specific Heat Capacity
(J g-1 oc-1)
2.2 4.2
Latent heat of
vapourisation (J g-1)
760 2257
Melting point (oC) -182 0
Boiling point (oC) -160 100
https://upload.wikimedia.org/wikipedia/commons/5/55/3D_methane.PNG
https://commons.wikimedia.org/wiki/Water_molecule#mediaviewer/File:Water_molecule.svg
Key chemical property that causes
the major differences seen in the
physical properties.
Methanogenic prokaryotes
• can be found in swamps,
wetlands, the guts of
animals (including cattle
and sheep)
• can also be found in waste
dumps

7. 2.2 U.2 Hydrogen bonding and dipolarity explain the cohesive, adhesive,
thermal and solvent properties of water.
Cohesive Properties
• Water is a polar molecule, with a negative oxygen end and a positive hydrogen end.
• Hydrogen bonds that exist between water molecules create a high level of
attraction linking water molecules together. This attraction between two of the
same molecules is called cohesion.
• These cohesive forces allow water to move up vascular tissue in plants against
gravity. It also creates surface tension on water that allows some organisms to walk
on water.
http://www.kellyisola.com/tag/transformation-2/

8. 2.2 U.2 Hydrogen bonding and dipolarity explain the cohesive, adhesive,
thermal and solvent properties of water.
Adhesive Properties
• Not only does water bind
strongly to itself, it also forms H-
bonds with other polar
molecules. This is
called adhesion.
• This is an important property in
transpiration as well, as water
adheres to the cellulose in the
walls of the xylem vessels
• As water is evaporated from the
stomata, the adhesion can help
the water move up through the
xylem
Capillary Action

9. 2.2 U.2 Hydrogen bonding and dipolarity explain the cohesive, adhesive,
thermal and solvent properties of water.
Solvent Properties
• Water is known as the “universal solvent” because of its ability to dissolve many substances
because of its polarity.
• Water is able to dissolve other polar molecules such as many carbohydrates, proteins and
DNA; and positively and negatively charged ions such as Na+.
• This is essential because it allows water to act as a transport medium (blood and cytoplasm)
of important molecules in biological organisms

10. 2.2 U.3 Substances can be hydrophilic or hydrophobic.
• All substances that dissolve in water
are hydrophilic, including polar
molecules such as glucose, and
particles with positive or negative
charges such as sodium and chloride
ions.
• Substances that water adheres to,
cellulose for example, are also
hydrophilic.
http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_7/glucose.jpg
hydrophilic
( water loving )
This term is used to describe substances
that are chemically attracted to water.
A space filling molecular diagram of glucose
showing the positive and negative charges

11. • Molecules are hydrophobic if
they do not have negative or
positive charges and are
nonpolar
• All lipids are hydrophobic,
including fats and oils
• Hydrophobic molecules dissolve
in other solvents such as
propanone (acetone)
http://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Water_and_oil.jpg/450px-Water_and_oil.jpg
hydrophobic
( water fearing )
This term is used to describe substances that are
insoluble in water
2.2 U.3 Substances can be hydrophilic or hydrophobic.

12. 2.2 A.3 Modes of transport of glucose, amino acids, cholesterol, fats,
oxygen and sodium chloride in blood in relation to their solubility in
water.
Blood Plasma
• Blood transports many different
substances to different parts of the body
using a variety of methods
• Water is critical both as a solvent in which
many of the body's solutes dissolve
• In addition, due to its polarity water is
a great solvent of other polar molecules and
ions. This is vital because it allows water to
act as a transport medium (blood and
cytoplasm) of important molecules in
biological organisms.
Plasma 55%
• 91% Water
• 7% Blood Proteins
• 2% Nutrients (amino acids, sugars, lipids)
• Hormones and ions
Cellular Components 45%
• White Blood cells
• Red Blood Cells

13. http://4.bp.blogspot.com/71TuXJIWv8o/UChT59p73
fI/AAAAAAAAAFY/B1zkMgT-dlA/s1600/Glucose.png
Glucose
• Glucose is polar making it a
soluble molecule in water,
making it possible to be
transported in the blood
plasma
• Blood plasma consists
mainly of water (95%) plus
dissolved substances which
it transports.
2.2 A.3 Modes of transport of glucose, amino acids, cholesterol, fats,
oxygen and sodium chloride in blood in relation to their solubility in
water.

14. Amino acids
• Positive and negative charges (due to the amine and acid groups) therefore soluble in water
• R group varies, can be polar, non-polar or charged
• R group determines the degree of solubility
• carried by the blood plasma
There is an internal transfer of a hydrogen
ion from the -COOH group to the -NH2
group to leave an ion with both a
negative charge and a positive charge.
http://chemwiki.ucdavis.edu/Under_Construction/Chemguide_(Jim_Clark)/Properties_of_Organic_
Compounds/XIII._Amino_Acids_and_Other_Biochemistry/A._Amino_Acids/2._Acid-
Base_Reactions_of_Amino_Acids
2.2 A.3 Modes of transport of glucose, amino acids, cholesterol, fats,
oxygen and sodium chloride in blood in relation to their solubility in
water.

15. 2. Fats
• Large, non-polar molecules
• insoluble in water
• They are carried in blood inside
lipoprotein complexes (in the plasma)
1. Cholesterol
• molecules are hydrophobic, apart
• from a small hydrophilic region at
one end
• This is not enough to make
cholesterol dissolve in water
• They are carried in blood in
lipoprotein complexes (in the
plasma)
3. Lipoprotein complex
• Outer layer consists of single layer of
phospholipid molecules
• hydrophilic phosphate heads of the
phospholipids face outwards and are in
contact with water
• The hydrophobic hydrocarbon tails face
inwards and are in contact with the fats
• cholesterol molecules are positioned in the
phospholipid monolayer - hydrophilic region
facing outwards
• Proteins are also embedded in the
phospholipid layer (hence the name)
http://chienlab.wikispaces.com/file/view/lip
oprotein.jpg/45882185/lipoprotein.jpg
2.2 A.3 Modes of transport of glucose, amino acids, cholesterol, fats,
oxygen and sodium chloride in blood in relation to their solubility in
water.

16. O = O
Oxygen
• Non-polar molecule
• Due to the small size of an oxygen
molecule it is soluble in water, but
only just
• water becomes saturated with
oxygen at relatively low
concentrations
• As temperature increases the
solubility of oxygen decreases
• At body temperature (37 °C) very
little oxygen can be carried by the
plasma, too little to support aerobic
respiration
• hemoglobin in red blood cells carry
the majority of oxygen
• Hemoglobin has (4) binding sites for
oxygen
https://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/1GZX_Haemoglobin
.png/480px-1GZX_Haemoglobin.png
Hemoglobin
2.2 A.3 Modes of transport of glucose, amino acids, cholesterol, fats,
oxygen and sodium chloride in blood in relation to their solubility in
water.

17. Sodium Chloride
• ionic compound
• freely soluble in water
• dissolving to form sodium ions
(Na+) and chloride ions (Cl-)
• carried in the blood plasma
http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.swf
2.2 A.3 Modes of transport of glucose, amino acids, cholesterol, fats,
oxygen and sodium chloride in blood in relation to their solubility in
water.

18. Bibliography / Acknowledgments
Jason de Nys