1. 18/09/2018
Water
LO: to explain how the structure of water influences its properties and importance for living organisms

2. What do you know about water?
2 mins to write as many facts about water as you can
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These digital clock timers countdown from either 2 minutes, 1 min 30secs or 1 minute. The timings of these cannot be easily changed, although the colour can be by simply selecting the entire ‘pile’ of shapes that makes them up, and then formatting the colours.
There is a bell timer at the end of the countdown, if this is not desired then enter the animation settings, and delete the animation that ends .wav from the animation listing.

3. The structure of water (H2O)
2 atoms of hydrogen covalently bonded to a molecule of oxygen
Polar molecule- electrons not evenly distributed across the molecule (hydrogens slightly positive, oxygens slightly negative)
Attraction between these charges forms hydrogen bond between water molecules.

4. How does the structure of water affect it’s properties?
High heat capacity
Large latent heat of vaporisation
Strong cohesion between water molecules
An important solvent
A metabolite in many metabolic reactions

5. High 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.
Importance to living organisms?
1kg of water

6. Importance to living organisms?
The bodies of living organisms are mostly made of water. This water in and around our cells absorbs a lot of heat energy without its temperature increasing much. The water ’buffers’ the heat changes.
Also an advantage for aquatic organisms as large bodies of water, like seas or lakes, do not change temperature as quickly as terrestrial environments.

7. Large latent heat of vaporisation
In a body of water some molecules of water are moving at faster speeds (have higher kinetic energy). Some have enough kinetic energy to escape the water, moving into the air, this is called evaporation.
When these fast moving molecules evaporate their energy goes with them, leading to the average kinetic energy of the water to decrease. This means the water cools down. The energy that is lost is called the latent heat of vaporisation.
Importance to living organisms?

8. Importance to living organisms?
Animals that are able to sweat can keep cool as the water in sweat evaporates off the surface of the animal.
Plants are also cooled when water evaporates from their leaves.

9. Strong cohesion between water molecules
Due to their polarity (charges), water molecules are attracted to each other, and form hydrogen bonds.
These hydrogen bonds help hold water together, so they can flow as a continuous stream. This is known as mass flow.
Importance to living organisms?

10. Importance to living organisms?
In plants, water moves up the xylem vessels as a continuous stream. This allows water to move from the roots to the top of the tallest trees.
Water cohesion leads to ‘surface tension’, making water behave as if there is a skin where the water meets air. This allows small animals to live on the surface of water bodies.

11. An important solvent
A solvent is a liquid that other substances (called solutes) can dissolve. The positive and negative changes of water attract other molecules causing them to separate from each other - dissolve.
When substances are dissolved in water they are free to move around and react with other molecules.
Importance to living organisms?

12. Importance to living organisms?
The metabolic reactions that happen inside all living organisms can only happen when the reactants are dissolved in water.
Substances being dissolved in water also allows them to be transported around the bodies of living organisms. E.g. glucose, CO2, urea in blood plasma, also mineral ions and sugars dissolved in water are transported in xylem and phloem in plants.

13. Condensation and Hydrolysis
A metabolite
Water molecules can also be involved in chemical reactions directly.
Condensation and Hydrolysis
Importance to living organisms?

14. Importance to living organisms?
Hydrolysis reaction are important in digestion of large molecules in animals
Condensation reactions are important in synthesis of important molecules such as proteins in living organisms.

15. Task: In pairs or threes create a poster about:
The structure of water
The properties of water
The importance of water to living organisms

16. Task: Create a mark scheme for the following question:
Describe and explain the roles of water in living organisms and as an environment for living organisms. (10 marks)

17. Task: You now have 15 mins to write an answer to the question.
Describe and explain the roles of water in living organisms and as an environment for living organisms. (10 marks)
Now swap your answers and use your mark schemes mark them