The document discusses the properties of key elements found in living things and water. It states that carbon, hydrogen, oxygen and nitrogen are the most common elements, while sulfur, calcium, phosphorus, iron and sodium are also needed. It then provides examples of the role of each element, including sulfur in amino acids, iron in hemoglobin, calcium in bones, sodium for nerve impulses, phosphorus in ATP and DNA. The document also discusses the polarity and hydrogen bonding of water molecules and how this leads to water's thermal, cohesive and solvent properties, which allow it to act as a coolant, medium for reactions and transport in organisms.

2. 3.1.1 State that the most frequently occurring chemical elements in living things are
carbon, hydrogen, oxygen and nitrogen.
Review ionic, covalent and hydrogen bonds
Some fun with elements
http://en.wikipedia.org/wiki/File:CHONPS.

3. 3.1.2 State that a variety of other elements are needed by living organisms, including
sulphur, calcium , phosphorus, iron and sodium
http://commons.wikimedia.org/wiki/File:Electron_shell_020_Calcium.svg
http://commons.wikimedia.org/wiki/File:Electron_shell_016_Sulfur.svg
http://commons.wikimedia.org/wiki/File:Electron_shell_015_Phosphorus.svg
http://commons.wikimedia.org/wiki/File:Electron_shell_026_Iron.svg
http://commons.wikimedia.org/wiki/File:Electron_shell_011_Sodium.svg

4. http://www.flickr.com/photos/csb13/1873194745/

5. 3.1.3 State one role for each of the elements
Sulphur is an important element in some amino
acids. It allows disulphide bonds to form in
proteins, influencing the protein’s shape
see HL 7.5 Proteins
What about iron?
http://commons.wikimedia.org/wiki/File:Granulated_sulphur02.jpg

6. Iron is in
haemoglobin, to
carry oxygen in
blood.
Calcium?
http://www.flickr.com/photos/csutka/3956855512/

7. Calcium is
in Bones!
Sodium?
http://www.flickr.com/photos/mugley/3491817141/

8. Sodium is
important
for nerve
impulses
See Core
6.5.5
Phosphorus?
http://commons.wikimedia.org/wiki/File:Nametal.JPG.jpg

9. Phosphorus is in ATP

10. And, of course, in
phospholipids in
cell membranes.
Here in Italian, just for a change.
See: Structure of the membrane 2.4.1
http://commons.wikimedia.org/wiki/File:Fosfolipide.svg

11. …and in
DNA, amongs
t other
things.
Also…
CHON!
http://commons.wikimedia.org/wiki/File:DNA_Structure%2BKey%2BLabelled.png

12. 3.1.4 Draw and label a diagram showing the structure of water molecules to show their polarity
and hydrogen bond formation.
Water is a weird and
freaky substance.
It is this way because
of its polar nature.
http://commons.wikimedia.org/wiki/File:Water_drop_animation_enhanced_small.gif

13. No,
that kind
http://commons.wikimedia.org/wiki/File:Eisb%C3%A4r_1996-07-23.jpg

14. The oxygen atom has 8
Revisit the Crash Course positive charges (protons)
Biology video “Carbon” (on at its nucleus.
slide 2) at the 8:08 mark Therefore it attracts the
shared electrons more
strongly and they spend
more time orbiting the O
-ve than the H.
O Thus water molecules are
polar, i.e. they have a
negatively charged pole
+ve H
(the oxygen) and a
positively charged pole
(the hydrogens)
H +ve

15. Hydrogen bonds
form when the
negatively charged
oxygen on one
molecule is
electrostatically
attracted to the
positive hydrogen on
another
http://commons.wikimedia.org/wiki/File:Liquid_water_hydrogen_bond.png

16. 3.1.5 Outline the thermal, cohesive and solvent properties of water
Thermal:
You know about the phases (states)
of water: Solid, Liquid and Gas.
Water changes from solid to liquid and
gas progressively as more energy (heat)
is added.
The weird thing about water is that it
takes more energy than it “should” to
change from one state to the next.
Why do you think that might be?
http://www.flickr.com/photos/westy559/328563694/

17. Extra energy is required
to overcome the
hydrogen bonds
We say that water has a
very high specific heat
capacity
It absorbs a lot of
energy before changing
state
http://commons.wikimedia.org/wiki/File:3D_model_hydrogen_bonds_in_water.svg

18. Cohesive
The polar nature of water makes it “sticky”
The molecules themselves stick together due
to hydrogen bonds (cohesion)
Water molecules stick to other
substances, e.g. glass (adhesion) for the same
reason
If water did not have this cohesive nature then it
would not form into drops like in the background.
Drops form because the cohesive forces are trying
to pull the water into the smallest possible
volume, a sphere.

19. Solvent
Water is sometimes called the “universal solvent”
Again, this is to do with the polar nature of water
Consider the sodium chloride below. The sodium and
chloride atoms are held together by ionic bonds.
NaCl Dissolving NaCl
http://commons.wikimedia.org/wiki/File:Sodium-3D.png
http://commons.wikimedia.org/wiki/File:Sodium-chloride-3D-ionic.png

20. Chlorine Water
Solvent Sodium
The polar water molecules have a stronger affinity for
both Na+ and Cl- than those ions do for each other.
So the Na and Cl “dump” each other and drift off with
the water molecules
NaCl Dissolving NaCl

21. The polar water molecules have a stronger affinity for both Na+ and
Cl- than those ions do for each other.
So the Na and Cl “dump” each other and drift off with the water
molecules.
Note how on the right of the diagram the oxygen in each water
molecule is close to the Na+ and the hydrogen in the water
molecules is close to the Cl-
NaCl Dissolving NaCl

22. All your
ion are
belong to
us!!!
Also, the relatively small size of
Check out the animation
the water molecules means that
they can “gang up” on the ions
(not to scale)
http://commons.wikimedia.org/wiki/File:Water_molecule.svg

23. 3.1.6 Explain the relationship between the properties of water and its uses in living organisms as
a coolant, medium for metabolic reactions and transport medium
Water’s thermal properties, its
high specific heat, means that it
can cool us.
Evaporating sweat (water
changing phase from liquid to gas)
takes heat away from the body
Water is also the main component
of blood plasma.
It transfers heat from the internal
organs to the skin.
http://www.flickr.com/photos/bukutgirl/205304794/

24. Cohesion allows plants to pull
water up their xylem via
transpiration
Adhesion aids
cohesion in
drawing water
up due to
capillary action
See HL Plant Science 9.2.6
http://www.flickr.com/photos/jaxxon/37559138/

25. Water’s solvent properties
mean that waste and nutrients
can be moved around by blood
in the veins and arteries.
It enables trees to
transport gases and
solutes as well
http://www.flickr.com/photos/roughgroove/3554305017/

26. Water’s nature as a solvent
means substances dissolved
in it can react with one
another.
The main component of
cytoplasm, where many
reactions occur, is water.
http://www.flickr.com/photos/cambridgeuniversity-engineering/5431155934/

27. Extension: Water as habitat
These water striders
rely on the cohesive
nature of water
resulting in surface
tension
http://www.flickr.com/photos/alexyo1968/4985953786/

28. Liquid water Ice
What are the implications of ice being less dense
(due to it’s highly organised crystalline structure)
than liquid water?
http://commons.wikimedia.org/wiki/File:Liquid-water-and-ice.png

29. Back to the bear…
I have somewhere to
stand and hunt.
See 5.2.6 to see why you
hoomans are worrying me!
http://commons.wikimedia.org/wiki/File:Eisb%C3%A4r_1996-07-23.jpg

30. Imagine if
ice sank
instead of
floated…
http://www.flickr.com/photos/toniblay/52925332/

31. Lakes at high latitudes would freeze from the bottom
up. Solid. And remain so for most if not all of the year at
high latitudes.
The seas would be similarly affected. The water that is
usually insulated by the ice, at above freezing
temperatures, would not exist.
There would be no habitat for the bottom dwellers.
In fact, the pressure of the overlying water would make
the water at the bottom freeze. Even in the tropics.

32. Lucky for us
water is the
way it is!

33. Further information:
Properties of water
Three of the best sites for
IB-specific Biology
information. The top link
takes you to the PPT by
Stephen Taylor