2. Review ionic, covalent and hydrogen bonds
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

3. 3.1.2 State that a variety of other elements are needed by living organisms, including sulphur, calcium , phosphorus, iron and sodium

4. CaFe NaPS!

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?

6. Iron is in haemoglobin; Iron is the oxygen binding component of blood
Iron is in haemoglobin; Iron is the oxygen binding component of blood. Also helpful in blood clotting
Calcium?

7. Calcium: used in structure of Bones and teeth
Sodium?

8. Also...found in some amino acids (NOT ALL)
Sodium is important
for nerve impulses
Also...found in some amino acids (NOT ALL)
See Core
6.5.5
Phosphorus?

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

11. …and in DNA, amongst other things.
Also…
CHON!

12. Water is a weird and freaky substance.
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.

13. No, not that kind of polar

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

15. Hydrogen bonds form when the negatively charged oxygen on one molecule is electrostatically attracted to the positive hydrogen on another

16. 3.1.5 Outline the thermal, cohesive and solvent properties of water
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?

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

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. NaCl NaCl 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
NaCl
Dissolving

20. Chlorine
Water
Solvent
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
Sodium
NaCl
NaCl
Dissolving

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
NaCl
Dissolving

22. All your ion are belong to us!!!
Also, the relatively small size of the water molecules means that they can “gang up” on the ions
(not to scale)
Check out the animation

23. Evaporating sweat (water
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.

24. Cohesion allows plants to pull water up their xylem via transpiration
xylem is derived from the Greek word meaning "wood";
the best-known xylem tissue is wood though it
is found throughout the plant.
Its basic function is to transport water
Adhesion aids cohesion in drawing water up due to capillary action

25. It enables trees to transport gases and solutes as well
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

26. The main component of cytoplasm, where many reactions occur, is water.
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.

27. Extension: Water as habitat
These water striders rely on the cohesive nature of water resulting in surface tension

28. What are the implications of ice being less dense
Liquid water
Ice
What are the implications of ice being less dense
(due to it’s highly organised crystalline structure)
than liquid water?

29. Back to the bear… I have somewhere to stand and hunt.
See to see why you humans are worrying me!

30. Imagine if ice sank instead of floated…

31. There would be no habitat for the bottom dwellers.
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:
We didn’t watch this in class but this is a good video