1. Bell ringer – Protein WS
Self asses the protein WS

2. Lesson objectives
explain how hydrogen bonding occurs between water molecules and relate the properties of water to its roles in living organisms

3. Properties of Water card sort
Match the properties of water with their use in living organisms

4. Ice is less dense than water Ice forms an insulating layer over water
Property:
Ice is less dense than water
Ice forms an insulating layer over water
High surface tension
The high surface tension of water means that it can form a habitat on the surface of the water
Strong cohesive properties and high tensile strength
Water can be pulled through plants in a column as the water molecules are held together by H-bonds
Colourless with a high transmission
Light can pass through cells for photosynthesis
Liquid at room temperature
Can be used for transport and a medium for reactions
In order to evaporate it must absorb a large amount of energy (high latent heat of vaporisation)
Can be used for cooling organisms by evaporation of for example sweat
Water can absorb a lot of energy for only a small rise in temperature (high specific heat capacity)
Conditions are stable in cells and aquatic environments

5. Properties of water
1. Use the diagram on the right to explain how hydrogen bonds form between water molecules. Explain how this affects the state of water at room temperature
2. The “sticky” nature of water is vital for many organisms.
a) State the correct term to describe this “stickiness” between water molecules.
b) explain how this helps pond skaters and plants.
3. Explain why water is used as the transport medium of the blood
4. Differentiate between specific heat capacity and latent heat of vaporization. Why are both crucial when discussing the properties of water?

6. State at room temperature
Water is a liquid at room temperature.
However, all other similar molecules are gases.
Hydrogen bonds form because of polar covalent bonding between the oxygen and hydrogen atoms H O +
2- H O +
2- H O +
2-
Hydrogen bonds act between the water molecules, and they attract them enough so that it behaves as a liquid. H O +
2-

7. Cohesion
Water molecules show a strong attraction to one another, this is called cohesion.
Droplets of water form spheres due to cohesion between water molecules

8. Surface Tension The surface of water can behave like an elastic sheet
The molecules in the bulk of the liquid are effected by various intermolecular forces of attraction
Those molecules in the surface are not effected by molecules above them, and therefore ‘pull’ together more strongly, effectively resembling a stretched membrane
A habitat can therefore survive on the surface of the water

9. Latent heat
While changing state, a substance will take in heat energy (solid  liquid  gas), or expel heat energy (gas  liquid  solid) without a change in temperature. This is termed Latent Heat.
Water has a large latent heat of vaporisation, and therefore absorbs a large amount of heat energy while changing from water to vapour.
Cooling mechanisms (large amount of heat is lost compared to small amount of water)
Freezing of water in aquatic organisms is less likely
temperature
evaporate
GAS
condense
LIQUID
melt
solidify
SOLID
time

10. Specific Heat Capacity
The heat needed to raise the temperature of 1kg of water by 1°C is termed the Specific Heat Capacity.
thermometer
Water has a large specific heat capacity, and therefore can absorb large amounts of heat energy before its temperature raises a significant amount.
Temperature within cells and bodies tends to be more constant than surroundings
Aquatic habitats show relatively stable temperature
1kg of water

11. Density of water Unlike other substances, water expands as it freezes.
Water molecules in ice form a rigid structure so that there is more space between them, this is seen as expansion as a whole H O
Ice
Water H O H O H O H O
Water molecules are able to approach one another quite closely
As water expands when it freezes, its density (mass per unit volume) will decrease.
This means that ice is less dense than water, and will therefore float on top of it.
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12. Testing for biological molecules
How could we test for:
Starch
Sugars
Proteins
Lipids

13. Reducing vs non-reducing sugars
Carbonyl group  reducing sugar

14. Sucrose cannot open back up  no carbonyl group  not reducing

15. Testing for biological molecules
Research the tests to identify starch, reducing sugars, non-reducing sugars, proteins, lipids
Prepare a table including the name of the molecule, the method and what a positive result looks like.

16. HW Tests for Biological molecules
Next lesson you will carry out practicals identifying biological molecules. Carefully read the instructions and prepare a risk assessment in form of the following table:
Hazard (Substance/equipment that might hurt you)
Risk associated with the hazard
How to avoid/ control the hazard